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Saturday, August 17 2019

Preference: Blend of the 00Z GFS/ECMWF, and GEFS/ECENS means
Confidence: Average

The large scale flow across the CONUS will remain broadly cyclonic
through the weekend, although gradual height rises are expected by
later Sunday and early next week across the central and southern
U.S. Shortwaves rotating through the flow will be the primary
sensible weather makers, and it is discrepancy among these
features that lead to the preferred blend.

The most notable differences involve the 00Z NAM which continues
to be a relatively strong outlier with several of these vort lobes
impacting the Plains/Midwest that are shedding around a complex of
upper lows in Canada. In fact, the NAM gradually becomes out of
tolerance with the global model consensus across much of
central/southern Canada by the end of the period
. The 00Z UKMET
also is problematic
with energy it has lifting up across the upper
Midwest through early Sunday as it is sharper and stronger with a
surface wave lifting up along a cold front crossing this region.
The UKMET also is out of tolerance across Canada versus the model
consensus, which is strongly supported at this point by the 00Z
GFS and 00Z ECMWF overall.

Across the Southeast and Mid-Atlantic coastal plain, a persistent
and quasi-stationary frontal zone is expected to be the focus for
multiple waves of low pressure
. One wave of low pressure will
eject northeast off the Mid-Atlantic coast and out to sea on
Saturday. Meanwhile, a second wave of low pressure situated
already down across northern FL will lift northeast very close to
the Southeast and southern-Mid-Atlantic coastline through Sunday
before then exiting offshore and out to sea on Monday. The 00Z
NAM, 00Z CMC and especially the 00Z UKMET intensify this low
center as it lifts northeast up the coast, with the 00Z GFS and
00Z ECMWF showing more modest development
. A large number of
Canadian ensemble members and a fair number of the GEFS members
favor at least a modest low center, with the vast majority of the
ECENS members more ill-defined. The 00Z NAM-conest, 00Z ARW/ARW2
solutions show a bit more development comparable to the NAM, but
the 00Z NMMB is a weak outlier.

There is strong support toward a GFS/ECMWF blend out of the latest
GEFS/ECENS means across the CONUS, and thus a blend of all of
these will be preferred at this point. However, a slightly
stronger version of the GFS/ECMWF solutions is suggested along the
Southeast and Mid-Atlantic coasts with the low center lifting
northeast across these areas on Sunday.

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Sunday, August 18, 2019

Quote

Sunday, August 18 2019
Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1256 AM EDT Sun Aug 18 2019

Preference: Blend of the 00Z GFS and 12Z ECMWF
Confidence: Average

A broad deep layer trough covers the northern half of the CONUS
with a few smaller scale shortwaves currently progressing through
the Midwest, Great Lakes and Northeast. The latest guidance favors
the deeper layer trough advancing east across the Midwest and
Great Lakes region through Sunday, before then brushing the
Northeast and retreating up across southeast Canada on Monday. In
general, the 00Z NAM again appears to be a tad more aggressive
than the global models with the details of the shortwave impulses.
On the larger scale, the guidance though appears to in reasonably
good agreement which includes the large scale trough evolution
over the northern U.S. and southern Canada
. However, the height
falls will send a cold front from the Midwest through the
Northeast which is then expected to stall out across the Ohio
Valley and Mid-Atlantic region on Tuesday. There are some
differences with respect to a couple waves of low pressure riding
northeast up along the front. The 00Z NAM and to a greater extent
the 12Z UKMET appear to be too strong with their wave activity
impacting the Midwest and Great Lakes region
.

In the wake of the trough, the flow will at least briefly flatten
out and allow a large 594+ dm ridge to expand across the Southwest
and much of the central and southern Plains. Once again though,
the UKMET has the strongest ridge axis out of all of the models
which has become a notable bias of the UKMET when it comes to
larger scale height rises/ridging in general. By the end of the
short range period, the large scale flow will become a bit more
amplified across the CONUS as a new upper trough digs southeast
across the upper Midwest and Great Lakes which will allow a new
cold front to settle southeast from Canada
. The 12Z ECMWF was a
tad slower than the model consensus with this next set of height
falls, but in general the model spread was relatively modest with
this and the next cold front.

Meanwhile, there will be an upstream trough approaching the
Pacific Northwest by the end of the period, and this is where
there is more substantial model spread, as the 12Z CMC is a
progressive outlier. Meanwhile, the 00Z NAM/GFS solutions both
have the core of their height falls digging a tad farther south
than the 12Z UKMET/ECMWF solutions which allows a rather strong
surface low to track a tad farther south by comparison toward
coastal areas of British Columbia. This energy will drive a cold
front to just offshore the Pacific Northwest by early Wednesday.

In the tropical confluence zone involving the central/eastern Gulf
Coast, Southeast and southern Mid-Atlantic region, there will be
multiple waves of low pressure that will need to be closely
monitored. One wave of low pressure just inland over far northeast
SC will be lifting northeast across the NC Outer Banks by early
Sunday afternoon and then well out to sea on Monday. The 00Z NAM
becomes the fastest solution with this, and the 12Z CMC the
slowest. Meanwhile, the 12Z UKMET is a strong outlier solution.
Meanwhile, there is evidence of a new compact area of low pressure
south of the FL Panhandle this evening which the global models and
hires guidance take gradually northward and inland by Monday. The
00Z NAM is the strongest of all of the solutions with this feature.

Based on all of the model spread and latest trends, a blend of the
00Z GFS and 12Z ECMWF will be preferred across the CONUS
, and
accounting primarily for the outlier solutions noted with the NAM
and UKMET for the time being. The latest ensemble guidance strongly
favors the GFS/ECMWF consensus. However, one exception is with
respect to the FL Panhandle low center as a general model blend
will be preferred with this feature. This will support a reasonably
well-defined low advancing north in off the Gulf of Mexico by Monday.

http://www.daculaweather.com/4_hpc_500mb_preferred.php
http://www.daculaweather.com/4_hpc_height_trends.php

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Monday, August 19, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
229 AM EDT Mon Aug 19 2019

Valid Aug 19/0000 UTC thru Aug 22/1200 UTC

...Overall Pattern Across the CONUS...

Preference: Blend of the 00Z GEFS mean/12Z ECENS mean
Confidence: Average

The main component of mid-upper level ridging in place at the
start of the period near the Rio Grande will translate westward to
just off of the Southwest coast by Wednesday afternoon. A small
portion of the ridge will remain over the south-central U.S.
Meanwhile, across the northern tier of the U.S., the flow is
quasi-amplified with a closed low over south-central Canada which
will track east and elongate east-west before re-amplifying
southward toward the Great Lakes late Wednesday. Back to the west,
an anomalous upper trough, forecast to be offshore of the Pacific
Northwest on Tuesday, will weaken slightly as it moves into
British Columbia and the Pacific Northwest Wednesday.

There are some minor timing differences with the upper trough in
the vicinity of the Great Lakes, but there are more concerns
regarding the depth of it. Firstly, the 00Z NAM appears to be a
tad too strong with some of the vort energy advancing east
underneath the trough as it crosses the OH Valley, Mid-Atlantic
and Northeast Tuesday and Wednesday. Regarding the larger scale
trough, the 00Z GFS becomes the strongest solution, with the 00Z
CMC the weakest. This translates accordingly to the same intensity
spread with the evolving surface low impacting southeast Canada.
Meanwhile, the 00Z ECMWF is seen as placing it surface and
mid-level low centers on the south side of the model consensus and
south of the 12Z ECENS mean. The 00Z GEFS mean is rather close to
the 12Z ECENS mean with this evolution, and suggests the
deterministic GFS is a strong outlier.

Farther south across the eastern Gulf Coast and the Southeast, the
00Z UKMET is still a bit of a strong outlier with the slowly
meandering low/mid-level low center near the FL Panhandle and
southern GA. The guidance overall suggests this energy will
gradually elongate and shear slowly off to the northeast over the
next couple of days across the Southeast.

Across the Pacific Northwest, the 00Z NAM and 00Z CMC are a bit
slower than the multiple model consensus, and also are a bit more
aggressive with their height falls versus the 00Z GFS and 00Z
ECMWF, although the GFS is a tad stronger and faster than the
ECMWF. Both the GFS and ECMWF are well supported by their
respective ensemble means regarding the depth and timing of this
system.

Based on the latest model spread, ensemble clustering and trends,
a blend of the ensemble means will be preferred across the CONUS
via the 00Z GEFS and 12Z ECENS means which should help to resolve
of the regional differences seen in the guidance.

 

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Because of the unsettled weather we have been having afternoon showers here in Candler County ( Metter).  Not a huge amount in most cases, but it cools us off.   

I am interested if they are looking for a big jump for the last week in Aug/1st week Sept since they are still predicting above normal?

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4 hours ago, RickyD said:

Because of the unsettled weather we have been having afternoon showers here in Candler County ( Metter).  Not a huge amount in most cases, but it cools us off.   

I am interested if they are looking for a big jump for the last week in Aug/1st week Sept since they are still predicting above normal?

The NHC upped the ante in their forecast last week, but unless something happens in the next week or two, it will most likely be a below normal hurricane season. 

 

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Tuesday, August 20, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
256 AM EDT Tue Aug 20 2019

Valid Aug 20/0000 UTC thru Aug 23/1200 UTC

Preference: Blend of the 00Z GEFS/12Z ECENS means
Confidence: Average

Mid to upper-level ridging will persist for the next couple of
days from the south-central to the southwest U.S., before the
ridging breaks down as a result of a split flow pattern that
develops across the CONUS
. The northern stream energy will
actually become increasingly amplified featuring two troughs, one
over the Pacific Northwest and another across the Midwest and
Great Lakes region. South of the belt of the westerlies will be a
southern stream featuring energy that digs into the Southwest by
later Thursday and Friday, and with a smaller scale shortwave
trough crossing the central Plains by that time.

Overall, the 00Z NAM tends to be a tad more amplified than the
global models with the northern stream trough impacting the
Northwest. The 00Z ECMWF trended a bit weaker from its 12Z run
which was more amplified, and so now the ECMWF is much more in
line with the model consensus. It should be noted that the 00Z
UKMET gradually becomes a weaker outlier as this energy ejects out
across the northern High Plains and crosses through southwest to
south-central Canada. Downstream across the Midwest and Great
Lakes, the 00Z NAM and 00Z CMC solutions gradually lag the
progression of the trough, and the CMC also gradually becomes a
more amplified outlier. However, with respect to the deep closed
low over southeast Canada, the guidance is reasonably well
clustered, although at the end of the period the CMC and to some
extent the UKMET were showing a bit faster closed low evolution
across Quebec.

Elsewhere, the NAM was noted to be a bit deeper with shortwave
energy advancing across the OH Valley and Mid-Atlantic region on
Tuesday and Wednesday. With respect to the southern stream energy,
the NAM was also seen as being a bit deeper than the global models
with both the energy over the Southwest and over the
central/southern Plains toward the end of the period. The NAM also
is the most aggressive of all of the models with energy and
possible low development over the Gulf of Mexico that rides
northwest up toward the southeast TX and LA coastal plain area by
Friday.

For the time being, the preference will be to lean toward a
consensus of the ensemble means for the CONUS per the 00Z GEFS
mean and 12Z ECENS mean to account for some of the regional model
spread, and especially with respect to the troughing ejecting out
toward the northern High Plains at the end of the period.

Orrison

Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

 

Today
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Wednesday, August 21, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
227 AM EDT Wed Aug 21 2019

Valid Aug 21/0000 UTC thru Aug 24/1200 UTC

Preference: Blend of the 00Z GEFS/12Z ECENS means
Confidence: Average

Mid to upper-level ridging will persist through Wednesday for the
next couple of days from the south-central to the southwest U.S.,
before the ridging breaks down as a result of a split flow pattern
that develops across the CONUS. The northern stream energy will
actually become a bit more amplified with two troughs of note. One
will impact the Pacific Northwest and northern Plains, with
another one over the Great Lakes region and Northeast. South of
the belt of the westerlies will be a southern stream featuring
energy that digs into the Southwest by later Thursday and Friday,
and with a smaller scale shortwave trough crossing the
central/southern  Plains and the lower MS Valley through Friday
and Saturday.

Overall, the 00Z NAM is a bit more progressive than the global
models with the troughing that ejects east across the northern
Rockies and High Plains by Friday, however, the 00Z ECMWF/CMC
solutions are the slowest solutions and also tend to be the
deepest. The 00Z UKMET is only a little more progressive than the
ECMWF/CMC camp, but the 00Z GFS splits the difference between the
faster NAM and the slower non-NCEP camp.

Downstream across the Great Lakes and Northeast, the models show a
fair degree of trough amplification and also drive a cold front
southeast across the OH Valley, Mid-Atlantic and Northeast. The
guidance is reasonably well clustered with this, but the 00Z UKMET
is a bit weaker than the remaining guidance.
 
Elsewhere, regarding the southern stream energy, the 00Z NAM is
seen as being a bit deeper than the global models with a focus in
particular on the energy over the central/southern Plains. The 00Z
GFS is also a bit on the deeper side of the guidance and is seen
as being slower with the shortwave evolution. The GFS is also a
bit deeper than the remaining guidance with the weakness that is
over the Southwest. Regarding the weak disturbance/trough lifting
northwest across the western Gulf of Mexico by Thursday and
Friday, the NAM overwhelmingly sticks out as a strong outlier
solution as it develops a well-defined low to mid-level low
center, and has a very strong QPF signal impacting southern LA.

For the time being, the preference will be to lean toward a
consensus of the 00Z GEFS mean and 12Z ECENS mean across the
CONUS
. This will provide a strong and well clustered compromise
solution with the details especially concerning the trough
crossing the Northwest and the northern Plains, and will help to
better resolve some the smaller scale spread seen with the
southern stream shortwave energy.

Orrison

Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Thursday, August 21, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
229 AM EDT Thu Aug 22 2019

Valid Aug 22/0000 UTC thru Aug 25/1200 UTC

Preference: General Model blend
Exceptions: Non-NAM in Northeast
            ECMWF/UKMET blend in Gulf/FL by Day 3
Confidence: Slightly above average except Gulf/FL (below average)

07z update: A slight slowing in the UKMET/ECMWF and availability
of the 00z CMC suggest the 00z GFS is a bit fast exiting with the
shortwave into the Central Plains on Sat into Sun, in line with
typical bias but still serviceable if tempered slightly in the
blend and so a general model blend could be supported at slightly
above average here.

The Great Lakes to Northeast cyclone continues to be strongly
agreed upon with exception of the 00z NAM, so will continue with
the same Non-NAM blend here at slightly above average confidence.

The SE Gulf/Florida wave continues to show moderate to high
spread, though the ECMWF has trended slightly stronger and
northeast of the GFS/NAM over the center of FL but still not as
deep as the UKMET, so will trend toward a UKMET/ECMWF blend but
still a below average confidence for this system.  As for TS Ivo,
a slight acceleration in the short-term in the 00z ECWMF over the
12z run, suggests a 50/50 blend of the ECMWF/GFS is closest to the
03z NHC forecast.

---Prior Discussion---
GOES-WV mosaic denotes two amplified troughs crossing the northern
portion of the CONUS and southern Canada.  The western system
continues to be quite impressively curved/compact crossing through
the lower Columbia River Valley; which is forecast to
break/stretch into a more positively tilted trof as the northern
stream accelerates eastward across Central Canada.  The global
guidance continues to present a very consistent and agreeable
development, even as the wave weakens crossing into the High
Plains Sat, giving way to upscale development of convection in
north-south moisture stream.  The UKMET is a bit slow here, and
the 00z GFS a bit fast, but overall a general model blend could be
supported with the evolution in this wave.

Further east, the deep, broader cyclone over James Bay is pressing
a weak shortwave through SE Ontario with a strong jet helping to
press the attendant surface front through the Great Lakes back
toward the the lower MO River Valley.   A secondary shortwave will
drop south out of Manitoba/W Ontario by early Friday, sharpening
the trof into a positively tilted trof across SE Canada into the
Southern Great Lakes. Eventually, by late Sat, the trailing edge
of the trof is expected to break into a small cut-off low across
New York into New England, this is a typically uncertain evolution
particularly in strength/depth and placement but the guidance is
fairly agreeable, though the 00z GFS shifted a bit faster (typical
of bias) relative to the UKMET/ECMWF.  Here, the 00z NAM is much
too strong in the northern portion of the wave and does not develop
as positively tilted, therefore with no wave break on the trailing
edge.  This evolution stands out against the ensemble and
deterministic suite to suggest a Non-NAM blend for this wave.

Elsewhere, there is moderate to high uncertainty to the
development of a surface reflection across S Florida by 12z Sunday
with the UKMET, over developed relative to other guidance (typical
of bias with these tropical systems).  The 03z NHC forecast for TS
Ivo, matches a blend of the ECMWF/GFS but closer to the 00z GFS.

Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Friday, August 23, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
315 AM EDT Fri Aug 23 2019

Valid Aug 23/0000 UTC thru Aug 26/1200 UTC

Preference: General model blend
Exceptions: 12z ECMWF/UKMET blend FL to off Carolinas Days 2/3
Confidence: Above average

07z update: The two northern stream systems continue to be in
remarkably strong agreement through 12z Monday with little change
in thinking/preference but increase confidence to above average,
this includes the interaction with the North-central Gulf wave
phasing with the digging northern stream trof Sunday into Monday.

As for the FL/Gulf Stream surface wave, the ECMWF shifted a tad
SE, but the UKMET trended nearly identical in placement/depth with
the ECMWF to boost confidence in the initial thinking.  The CMC,
while still well weaker than the ECMWF/UKMET, did shift the energy
northeastward in step.  A such will increased confidence in a 00z
ECMWF/UKMET blend to slightly above average.


---Prior Discussion---
Deterministic guidance continues to have very strong model
agreement with the synoptic flow across the CONUS through early
Monday, with the Northern Rockies trof beginning to expand across
the Northern Plains with some energy leaking southeast into the MS
Valley potentially enhancing a weak surface wave/trof in the
Western Gulf by 12z Monday.  The only minor difference in the mass
field, is seen in the 00z NAM where, the upper tor across S Canada
is much broader and therefore a bit deeper than the other
guidance.  Across the Northeast, the positive tilt trof begins to
exit, but with enhancing ridging to the south, the trailing
portion of the trof breaks into a weak closed low in the Northeast
by 12z Monday, with the 00z GFS a bit east of the remaining
guidance, with little effect in the lower troposphere.  This leads
to a general model blend working for much of CONUS, with perhaps
that lower weighting of the NAM at the day 3 period in the
Northern Plains.  Confidence is slightly above average confidence
for this blend.

The remaining uncertainty continues with the evolution of the
tropical/sub-tropical wave developing in Florida early Sunday and
deepening as it intersects with the languishing frontal zone along
the Gulf Stream off the east coast into Monday.  Here, the 00z NAM
has trended toward the earlier preference of the 12z ECMWF/UKMET
depicting a stronger wave, yet the NAM is slower to lift out and
up the coast, so the NAM adds confidence to the solution but will
still prefer the ECMWF/UKMET blend here.  The 00z GFS had not
budged, suggesting maybe a weak closed low at the apex of the
tropical wave, but continues to press it west into the Gulf, like
the 00z CMC.  Confidence is average in this area of the CONUS.

As for TS Ivo in the EPAC, the 00z GFS continues to track closest
to the 03z NHC forecast track though closer to the 00z NAM and 12z
ECMWF, so a blend of the 3 may be best to approximate the official
NHC track for Ivo and the moisture it pumps north into NW Mexico
and the Southwest.

Gallina

Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Saturday, August 24, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
221 AM EDT Sat Aug 24 2019

Valid Aug 24/0000 UTC thru Aug 27/1200 UTC

Preference: General model blend
Exception(s): 12Z UKMET/ECMWF FL and off Carolinas Days 2/3.
              Non-UKMET across Northern Tier Day 2/3.
Confidence: Slightly above average
            Average for surface low off Carolinas.


07z update: The 00z ECMWF and UKMET both trended a bit weaker for
the FL/Carolina near waters cyclone, more in line with initial
thinking that the 12z runs were a bit too strong, but the
placement/timing remains solid for continued preference.  The 00z
CMC remains weak.

The UKMET continues to be stronger/further south with the closed
low/surface wave across the northern tier and with the 00z
ECMWF/CMC keeping with continuity, will suggest continuing a
Non-UKMET blend for this system.

---Prior Discussion---
Strong model agreement continues through this forecast period
again providing solid confidence across much of the CONUS
.  There
are small detail differences across the northern tier on Day 3,
with the 12z UKMET a developing/deepening a bit further south,
enough to displace it within the larger guidance suite.  The 00z
NAM and GFS trended a bit more amplified with the secondary
shortwave crossing SW Canada late Monday to reinforce the
broadening closed low into the Red River Valley and south central
Canada by 12z Tuesday, but to limited negative effects.

As the northern stream trof amplifies and digs into the lower
Mississippi River Valley and interacts with the northeastward
shifting tropical wave, the NAM is a bit more separated and
stronger with each feature (typical of bias)
.  This delays its
eastward progression across the Gulf Coast states, relative to the
GFS/ECMWF/CMC, thought the UKMET is slower with the moisture
stream allowing for some agreement in the QPF placement, this is
less preferred overall.

The 00z GFS continues the short-term trend toward at least
placement of the surface wave moving out of FL into the Gulf
Stream off the Carolina coast Sun into Monday.  Like the 12z CMC,
the GFS is quite weak but shows at least some confidence in the
tracking/timing.  The ECMWF/UKMET both continue to be very strong
with the wave and slightly faster.  Thinking both may be a bit too
strong/deep but still favor a blend of the UKMET/ECMWF over other
guidance blends.  The 00z NAM is now the slowest, but is middle
ground in strength/depth.  Confidence remains average for this
system given the modest remaining spread, especially in strength.

Overall spread continues to reduce with respect to TS Ivo, until
late Day 2 into Day 3.  This is when the surface cyclone will be
weakening/becoming shallow, so steering flow will be highly
determined by remaining convection/depth, so the 00z GFS continues
to be quickest to remove convection and so the surface wave stalls
relative to the remaining faster ECMWF/UKMET.  NHC forecast seems
to jive best with the GFS/NAM and ECMWF.   The GFS continues to be
the most eastward with the moisture feed into the desert Southwest
and given its track record over the last day or so, it seems more
likely to weigh the GFS highest in blends for this area.

Gallina

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Sunday, August 25, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
228 AM EDT Sun Aug 25 2019

Valid Aug 25/0000 UTC thru Aug 28/1200 UTC

Preference: General model blend weighted toward 00z ECMWF/GFS/CMC
Confidence: Above average becoming slightly above average by Day 3

07z update:  The 00z UKMET showed significant improvement shifting
north; however, it is a deeper solution and therefore tucked west
with the surface wave relative to the ECMWF/GFS.  This is a minor
difference that would be fine blending out and supporting a
general model blend weighted to the new 00z ECMWF/CMC and the GFS.

---Prior Discussion---
The tightly packet deterministic guidance that had been consistent
for the past few days with the large/high-amplitude northern
stream trof digging across the Plains into Lower MS Valley has
become a bit less agreeable, more typical of the spread given the
pattern, especially at intersections with other streams (like out
of the Western Gulf), where phasing/timing is tricky.
 The
disagreement in the northern most portion of the trof, with the
closed low, in Southern Canada and the northern Tier, continues to
be mostly a displacement south of the UKMET.  The 18z GFS joined
the UKMET, but the 00z GFS shifted back north until the low
becomes quite mature into late Tues/Wed.  The ECMWF/ECENS are well
north of the GFS but still show best consistency and agreement,
though the 18z GEFS showed some more similarities to suggest the
GFS/ECMWF and their ensembles, as well as inclusion of the 00z NAM
is preferred for this portion of the system.


...Shortwave Crossing KS, Lifting through Great Lakes and Pressing
Cold Front into Upper Ohio Valley...


Preference: General model blend
Confidence: Slightly above average

07z update:  The issues with CMC have become better resolved,
while still presenting a stronger triple point (like the UKMET),
it does not appear to have a negative result on the sensible
weather, so a general model blend could be employed for this
portion of the wave.  This also includes the slowly sinking tail
end to the cold front and QPF axis across the Central then
Southern Plains (Red River) by 12z Wed.

---Prior Discussion---
Further south, through the Central Plains, as the MCV/shortwave
currently in KS starts to shear and lift back through IL into the
Great Lakes late Monday into Tuesday; the 12z CMC shows some
negative over amplification bias as the system deepens through the
Great Lakes and even dominates the closed low further west,
shifting the whole cyclone east, well departed from the ensemble
suite/remaining guidance.   The 00z NAM is a bit stronger and
delays the frontal zone push eastward relative to the other
guidance but not significantly and blended with the typical fast
bias of the GFS suggests, a non-CMC blend is preferable here.


...Western Gulf Tropical Wave/Phasing with Base of Northern Stream
Trof...


Preference: General model blend weight slightly more to 00z GFS
Confidence: Average

07z update:  The 00z ECMWF trended a bit less active with the
tropical wave and therefore is much weaker.  While it is still a
bit deeper than the GFS/NAM and CMC, it has a partner in the UKMET
which seems equally plausible.  The timing of the ECMWF with the
other guidance pressing the phased trof through the southeast fits
well with a general model blend, but still favoring the GFS a bit
more in the blend overall.

---Prior Discussion---
The base of the trof, shows the greatest spread in its interaction
with the tropical wave lifting through the Western Gulf into LA
later today.  The 12z ECMWF, shows very strong convective
development of the wave even with a surface inflection that lifts
north into TN/Cumberland Plateau, which is too intense and depicts
a very strong QPF response that is overdone as well.  The 00z NAM
along with the 12z UKMET and CMC support greater strength in the
sheared trof along the Gulf Coast as the two streams meld by
Tuesday.  The 00z GFS also trended this direction but are weaker
than the NAM/UKMET.  Continuity and trends would favor the GFS
slightly in a non-ECMWF blend for this tropical wave.


...Tropical/Subtropical Wave off Florida, lifting along Gulf
Stream...


Preference: Non-NAM blend
Confidence: Average

07z update: The 00z ECMWF trended a bit slower and weaker and
looks very similar to the GFS even depicting a slight westward jog
toward 12z Wed due to the approaching height falls and connecting
to the old frontal zone.  The 00z UKMET and CMC both start a bit
east of the GFS/ECMWF and meander similar to the GFS/ECWMF pair
but slightly east through each forecast step, with the UKMET a bit
faster than the CMC.  A GFS/ECMWF blend could be employed but to
cover the modest spread a non-NAM solution is preferred at average
confidence.

---Prior Discussion---
Along FL east coast through the Gulf Stream, the tropical invest
area continues to show solid continuity of a deepening surface
wave, however, the depth of the wave continues to trend slightly
weaker and slower lifting east-northeast.  The 00z GFS matches
placement and timing with prior run, along with the weaker
UKMET/CMC, but the 12z ECMWF is clearly still fastest and
eventually deeper by 12z Wed too.  The 00z NAM also continues to
be very slow...so would prefer a 00z GFS/UKMET/CMC blend for this
wave at average confidence.

Gallina

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Monday, August 26, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
226 AM EDT Mon Aug 26 2019

Valid Aug 26/0000 UTC thru Aug 29/1200 UTC

Preference: General model blend
Confidence: Above average through 78 hrs slightly above average
after
Exception: Coastal Low: 00z GFS/NAM (slightly below average)

07z update: The mass fields, with a small exception of the
Atlantic Coastal surface low (see 2nd paragraph), are in
remarkable agreement particularly through 72hrs across the CONUS.
Again, by 84 hrs, the UKMET and NAM are still a bit too fast with
the second Canadian shortwave but that is minor.

The surface low of the Northeast continues to befuddle the
guidance with a substantial variance noted by the UKMET, CMC and
ECMWF from prior runs
.  The interesting point though is they are
very agreeable with each other, so there may be a critical piece
of data added to their assimilation that missed the NAM/GFS (which
are also in strong agreement with each other).  A slightly
vertically deep cyclone in the new non-NCEP suite, suggests the
surface low does a tricordial wobble with the anticyclonic loop of
the 5H low (even manifest by the 00z NAM).  This does not make it
any clearer on which direction to take, but the interests along
coastal New England will see a much different forecast.  At this
point, will not deviate too much from initial
preference/continuity of the 00z GFS/NAM but reduce confidence to
slightly below average for this wave.


---Prior Discussion---
The 00z NAM/GFS continued another cycle of consistency and strong
deterministic guidance agreement with the synoptic
pattern/evolution over the CONUS
.   As with any run, there are
some very small scale amplitude differences, as well as,
differences due to convective development/feedback.  The largest
differences in the mass fields/QPF axes, are driven by slight
timing differences with the frontal zone crossing the Northeast
and the interaction with the moisture feed from the the
tropical/subtropical surface wave to the Southeast Wed into Thurs.
The UKMET is a bit faster and it along with the 00z NAM suggest
slightly earlier deep moisture flux for some heavy rainfall across
SE ME.   This is interesting, given the spacing between the UKMET
and NAM is probably the largest spread with the surface wave, and
the UKMET is stronger than the NAM. Overall, the deep closed low
in S Canada and the frontal zone spread is small enough to support
a general model blend, but the surface wave off the coast has
moderate spread.  The ECMWF has once again become fast and strong,
paired closest to the UKMET, while the GFS and NAM are weakest and
draw westward due to the approaching height-falls.  The CMC also
bends left but is very strong by the end of Day 3, which does not
seem a good fit to continuity and the ensemble suite.  Overall
would favor a NAM/GFS solution with some lower weighted UKMET and
some ECENS/GEFS mean in the blend.

Elsewhere, there is a small timing issue with a strong shortwave
across NW Canada on Day 3.  The 00z NAM and 12z UKMET are too
fast, though with little sensible affect to even the northern tier
of the CONUS, but would shade away from those in a larger scale
blend.  So overall a general model blend is supported, with only
exceptions noted above, with an above average confidence through
about 60 hrs before reducing to slightly above average afterward.

Gallina

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Tuesday, August 27, 2019

Obviously a little late on this one today...

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
101 PM EDT Tue Aug 27 2019

Valid Aug 27/1200 UTC thru Aug 31/0000 UTC

12Z Preliminary Model Evaluation with Preferences and Forecast
Confidence

Preference: General model blend
TD 06L NHC Proxy: 00z UKMET/00Z GEFS blend
Confidence: Slightly above average

For TD6 moving northeast off the eastern coast of the CONUS
through the period, the NHC track is a bit slower than the
majority of the available global suite. However, a blend of the
UKMET and GEFS mean produces something reasonably close to the
track as these are on the slow edge of the envelope. The trend in
the ECMWF has been towards this slower solution over the past 3
runs, so some weight on the ECMWF is usable, but will end up with
something that gradually gets more away from the official track.
For this reason, a UKMET/GEFS blend is suggested. This will also
play a role in the QPF, especially across eastern New England
Thursday as interaction with the approaching front has the
potential to produce heavy rainfall. The UKMET is the most
aggressive with QPF, and despite its typical wet bias, it being
the best deterministic model towards the track suggests an
increasing likelihood for heavy rainfall, so from a QPF standpoint
a general model blend is acceptable here.

Elsewhere across the CONUS, there is generally good agreement in a
western ridge/eastern trough generally becoming more zonal by day
3. While subtle differences exist in timing and intensity of
features which will eventually describe the synoptic shift, the
spread appears minimal. The biggest discrepancies lie in the
amplitude of the western ridge early in the forecast period, but
overall the QPF along the stalled front in the south and height
anomalies by day 3 feature a small envelope, so a general model
blend should be sufficient.

Weiss
Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Wednesday, August 28, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
237 AM EDT Wed Aug 28 2019

Valid Aug 28/0000 UTC thru Aug 31/1200 UTC

.Preference: General model blend
 Exception: Non-NAM QPF in Central/Southern Plains Day 3
Confidence: Slightly above average
Best NHC Proxy (Erin): 18z GFS or 00z GFS/NAM/UKMET/CMC blend
(Dorian)D3: 00z ECMWF

07z update:   The 00z CMC trended a bit slower and further south
in the Western portion of the CONUS and into SW Canada, enough to
support a general model blend through the bulk of the CONUS (with
the continued exception of QPF from the NAM in the
Central/Southern Plains on Day 3.

While the 00z ECMWF trended slower with 06L (Erin) lifting north
and now is about the same latitude of the official NHC forecast,
but still well west of it.  The remaining guidance, including the
00z CMC/UKMET/GEFS mean match the 00z GFS/NAM and are along the
forecast track but about 2-3hrs slower than it.  Would suggest
utilizing a non-ECMWF proxy toward the official forecast, or
remain with the 18z GFS which remains closest.  As for 05L
(Dorian), the 00z ECMWF shifted north and is in line with the
official 03z NHC forecast in the 72-84hr time period (31-00z to
12z) and so is considered the best proxy for the forecast.


---Prior Discussion---
The synoptic pattern continues to be very strongly agreed upon
through the first 2+ days particularly
, with the strong/deep
closed low across Ontario.  Its associated frontal zone is, also
well agreed upon on depth/timing until there is interaction with
the approach of TS Erin.  Erin remains very sheared with large
convective complex near the inner core/surface wave but also has a
very elongated northerly surface trof that is already shifting
toward the approaching height falls.  The 12z ECMWF is most
aggressive now, faster and closer to the coast while the 00z NAM,
12z UKMET and CMC are slower but much closer in placement.  The
18z GFS is very close to the official 03z NHC forecast and is best
to use as NHC best proxy; the 00z GFS, slowed a fraction but
matched closest to the CMC, so it is just south of the official
forecast.  So use of the 18z GFS is the best mass proxy to the
official forecast.

By 60hrs, the 12z CMC starts to break down compared to the
remaining guidance particularly with the approaching
shortwave/closed low nearing SW Canada by 84hrs.  The CMC is a bit
further north overall with increased pumping of the downstream
ridge in the Rockies which starts around 60hrs.

At the tail end of the frontal zone crossing the northern
tier/Great Lakes on Thursday and Friday intersects with the return
moisture stream over the Central Plains, and mass fields are quite
agreeable through Sat as well, however, the 00z NAM and lesser so
the GFS suggest greater southward propagation likely on stronger
LLJ/inflow than the UKMET/CMC/ECMWF.  The NAM becomes particularly
out of phase in the QPF axis to suggest a lower weighting or
removal at the end of Day 3 in this area though the remaining mass
fields are less affected than the QPF axis.

Tropical Storm, forecast hurricane by Day 3, Dorian is expected to
enter the Northern Bahamas/Southern Sargasso Sea.  Moderately
sizable spread remains in placement and strength.
 However, the
NAM/CMC are much too far south to the official 03z forecast.  The
GFS/UKMET are north of the forecast track (fast/slow,
respectfully) while the ECMWF is timed ideally in longitude but a
shade south.  As such, a blend of the GFS/UKMET and ECMWF provides
a good placement blend,
but a straight blend of the 3 (ie not
retaining the shape/depth/etc)...so re-centering and blending to
the common point would be the best proxy to keep the integrity of
the system as a whole.

Gallina

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Thursday, August 29, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
305 AM EDT Thu Aug 29 2019

Valid Aug 29/0000 UTC thru Sep 01/1200 UTC

Preference: non-00Z NAM blend led by the 00Z ECMWF
Confidence: Slightly above average

...07Z update...

Spread remains in the latest guidance across the central U.S. with
the 00Z NAM continuing to stand out the greatest (see below).
Adjustments by the 00Z UKMET/CMC appear to be positive although
the 00Z UKMET remains flat with the 500 mb trough across the Ohio
Valley. A non 00Z NAM blend of guidance with heavy weighting
toward the 00Z ECMWF is preferred across the central U.S., while a
general model blend can continue to be used elsewhere across the
lower 48.

...previous discussion follows...

The southern end of longwave troughing over the Great Lakes/Ohio
Valley at the start of the period is forecast to lift
northeastward through Saturday while lower amplitude longwave
troughing redevelops just east of the Mississippi River Sunday
morning. Meanwhile, mid-upper level ridging over CA/AZ will
translate toward the Four Corners region through Sunday morning as
a shortwave nears the Pacific Northwest Sunday morning.

Some of the greatest differences across the CONUS are across the
central U.S. are with the western end of a frontal boundary across
the central Plains. A MCS is forecast to develop over eastern
Nebraska/Kansas late Thursday night which has implications on the
latitude of the effective front into Friday night and Saturday.
The 00Z NAM is the most aggressive with the boundary sinking well
south into the southern Plains. The 12Z ECMWF appears to be the
most reasonable regarding run to run continuity and agreement with
the latest ensemble means. At 500 mb, the 12Z UKMET/00Z GFS appear
to be flatter/faster (respectively) with the corresponding trough
axis Saturday morning. The 12Z UKMET appears to have convective
feedback while the 12Z CMC is an outlier with its northern surface
wave position through Sunday morning.

Elsewhere across the CONUS, a general model blend is preferred
given good agreement.


...Tropical Depression Erin...

Preference: 00Z NAM/UKMET/CMC closest to 03Z NHC advisory
Confidence: refer to NHC

...07Z update...

The 00Z ECMWF adjusted toward the weaker 00Z GFS regarding the
surface low of what is currently Tropical Depression Erin.
Meanwhile, westward shifts in the 00Z UKMET/CMC make these models
close enough to the 03Z NHC advisory to allow inclusion as part of
a blend, excluding the 00Z GFS/ECMWF.

...previous discussion follows...

The 00Z GFS is a bit of an outlier with the strength of Erin
through Friday depicting a weaker system relative to the remaining
deterministic guidance. The 12Z UKMET/CMC are displaced east of
the 03Z advisory NHC track while the 12Z ECMWF/00Z NAM are closest
to NHC.


...Hurricane Dorian...

Preference: Blend of 00Z GFS/ECMWF/CMC closest to 03Z NHC advisory
Confidence: refer to NHC

...07Z update...

Shifts in the 00Z UKMET/CMC were slower compared to their previous
cycles while the 00Z ECMWF only made minor adjustments. A blend of
the 00Z ECMWF/CMC/GFS places a position nearest to the 03Z NHC
advisory track for Hurricane Dorian.

...previous discussion follows...

The 00Z GFS, 12Z ECMWF and 12Z UKMET are closest to the 03Z NHC
advisory track regarding Hurricane Dorian through about Saturday
morning. After this point in time, the 00Z GFS deviates north and
west of the NHC forecast positions but the 12Z ECMWF/UKMET remain
close to the NHC track.
The 12Z CMC is a faster outlier with
Dorian while the 00Z NAM is slower with the track.

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Friday, August 30, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
307 AM EDT Fri Aug 30 2019

Valid Aug 30/0000 UTC thru Sep 02/1200 UTC

00Z Final Model Evaluation, Confidence, and Preferences

Preference: 00Z GFS/CMC/ECMWF with some UKMET
Confidence: Above Average through 48 hours, Slightly Below Average
day 3

07Z Update: Other than the NAM, the global suite continues to be
in very good agreement with the evolution of the large scale
western ridge/eastern trough through Saturday
. On Sunday, guidance
diverges considerably with energy rotating onshore the PacNW. The
GFS/CMC remain very well clustered with a slightly faster and
weaker shortwave moving to the east, while the ECMWF and UKMET
have shied away from their previous slower/stronger solutions to
something closer to the GFS/CMC. While the highest weight in the
preferred blend should still be placed on the more consistent
GFS/CMC
, the ECMWF and UKMET are usable for day 3.

Previous Discussion:
Through the first 48 hours, the guidance is in very good agreement
that a broad longwave trough will persist in the east, while
ridging continues in the west. Small scale disturbances within the
flow may cause periodic rounds of convection of which the models
differ on latitudinal placement and QPF, but really only the NAM
is an outlier by being too deep with its trough
. By day 3, the
guidance differs considerably with handling of a mid-level trough
approaching the PacNW. The NAM/UKMET close off the low to maintain
a positively tilted trough axis west of the CONUS, the CMC/GFS
move a weaker shortwave onshore WA/BC, while the ECMWF is
somewhere in between. The differences seem to arise from vastly
different jet intensities and placement as no fewer than 3 jet
streaks interact over the northern Pacific Ocean. The GFS/CMC seem
to handle the cross polar jet most similarly, but confidence is
reduced by day 3.


...Hurricane Dorian...

Please refer to the official National Hurricane Center forecast
track

The guidance which most closely resembles the NHC track for
Hurricane Dorian is the 00Z ECMWF/CMC which are nearly on top of
the 03Z advisory points
. The UKMET is in much better agreement now
than its previous runs, but still slow compared to NHC and the
preferred blend.

Weiss

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

 

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Saturday, August 31, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
323 AM EDT Sat Aug 31 2019

Valid Aug 31/0000 UTC thru Sep 03/1200 UTC

00Z Final Model Evaluation, Confidence, and Preferences

Preference: Non-NAM, Non-CMC blend
Confidence: Above average

07Z Update: The primary discrepancies in the synoptic pattern
involve a shortwave moving into the Pacific NW on day 2 and then
into the Northern Plains Monday. The NAM and CMC are now both fast
outliers racing this feature eastward, far outpacing the remaining
global suite. Otherwise, the models are well clustered across the
CONUS.

Previous Discussion:
The global suite remains in good agreement in a
western-ridge/eastern-trough setup through the next 3 days. While
small scale perturbations in the flow will impact QPF, there is
generally small spread among the majority of the models. The lone
exception is the 00Z/31 NAM which becomes too fast and amplified
with a shortwave moving into the Pac NW on day 2, and lifting into
the northern Plains by day 3. This has the effect of pushing the
associated surface low and cold front too quickly east and too
sharply to the south, and for this reason the NAM is removed from
the preferred blend.

Otherwise, the preference this cycle includes all other available
guidance, accounting for the typical biases.


...Hurricane Dorian...

Please refer to the official National Hurricane Center forecast
track

Initially, the GFS/ECMWF are the best proxy for the NHC track for
Hurricane Dorian. However, by day 3, the GFS becomes too fast
while the UKMET/ECMWF slow across the Bahamas to become more
aligned with 03Z advisory positions. For this reason a
GFS/ECMWF/UKMET blend is preferred to maintain integrity of the
NHC track, but note more weight on the GFS the first 48 hours,
trending towards higher UKMET on day 3.

Weiss

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Sunday, September 1, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
346 AM EDT Sun Sep 01 2019

Valid Sep 01/0000 UTC thru Sep 04/1200 UTC

00Z Final Model Evaluation, Confidence, and Preferences

Preference: 00Z GEFS/00Z ECMWF/00Z NAM
Confidence: Average

07Z Update: Little differences noted in the 00Z Non-NCEP suite.
There remains above normal spread in the Northwest late on Day 2
into Day 3 which causes some lowered confidence, but the
preferences remain the same.

Previous Discussion:
The overall synoptic pattern will persist with a ridge in the west
and a trough in the east. While the guidance is well clustered in
the broad evolution, there are significant differences that arise
in day 2, and even moreso on day 3, across the NW and northern
tier. A shortwave moving into the PacNW will eject eastward Monday
into Tuesday, with shortwave ridging developing quickly in its
wake. The CMC is very quick to push this energy eastward,
outpacing the global consensus considerably. The GFS is on the
other side of the spectrum, with the shortwave moving so slowly
that it hangs back and cuts off into a mid-level low where the
remaining guidance has upstream ridging. This seems unlikely as
the flow across the northern tier is modestly fast embedded within
a 90 kt upper jet. The UKMET is usable, but its heights are a few
dm higher as it maintains the strength of the ridge more strongly
than the remaining guidance. The new NAM looks very much like the
ECMWF and the 18Z GEFS mean, bringing some consistency to
otherwise messy 60-84 hour mass fields.


...Hurricane Dorian...

Please refer to the official National Hurricane Center forecast
track

The ECMWF/UKMET/GFS are very tightly clustered to the 03Z NHC
track into day 2. After 48 hours, the best proxy blend begins to
diverge such that the GFS/UKMET are closest to the NHC track, and
late into day 3 the GFS alone is the best proxy as the UKMET is
too far west, and the ECMWF is too slow. So initially, the 3
models create the closest blend, slowly transitioning to the GFS
on day 3.

Weiss

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

 

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Monday, September 2, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
342 AM EDT Mon Sep 02 2019

Valid Sep 02/0000 UTC thru Sep 05/1200 UTC

00Z Final Model Evaluation, Confidence, and Preferences

Preference: Non-NAM blend
Confidence: Average

07Z Update: The Non-NCEP 00z Suite showed little change from the
12Z, so the preferences remain unchanged. The UKMET may be a bit
amplified compared to the consensus in the depth of the shortwave
moving across the northern tier, but remains well within the
ensemble envelope so can continue within the preferred blend.

Previous Discussion:
The models are in good agreement that the longwave synoptic
pattern will maintain a ridge in the west and a trough in the
east. There is little variation in the guidance, and the features
determining the preferred blend are generally smaller scale. The
NAM deepens the eastern trough a little too much when compared to
the global consensus. and is also much flatter with heights across
the NW. Otherwise, the 00Z GFS and 12Z Non-NCEP suite are well
clustered despite small temporal differences in a shortwave moving
eastward from the PacNW into the northern tier. Despite these
differences, QPF fields are well aligned so a blend which includes
all of the global suite except the NAM is reasonable.


...Hurricane Dorian...
A blend of the 00Z ECMWF/00Z UKMET/00Z GEFS mean provides the best
proxy to the 03Z NHC advisory track. The 00Z GFS deterministic is
very closely tied to the track through 48-60 hours, but then
becomes a bit fast and left of the track, while the GEFS mean
remains nearly on top of the forecast points, so is preferred more
than the operational run.

Weiss

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Thursday, September 12, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Thu Sep 12 2019

Valid Sep 12/0000 UTC thru Sep 15/1200 UTC

00Z Final Model Evaluation, Confidence, and Preferences

Preference: General model blend
Confidence: Average

08Z Update: The rest of the 00Z guidance showed fairly good
agreement across much of the CONUS with respect to the large scale
mass fields. However the one exception is with the tropical
disturbance over the Bahamas. The non-NCEP guidance all shift
eastward with the low tracking off the Florida coast through Day
3. This is in contrast with the GFS (near central Gulf of Mexico
by Day 3) and NAM (off the western FL peninsula). For now, will
prefer a consensus approach with the low tracking across the FL
peninsula and potentially across the panhandle through Day 3, but
admittedly the forecast confidence here is below average.

---previous discussion---
The synoptic pattern over the CONUS features an anomalous upper
level trough over the northern Rockies and northern Plains with a
strong ridge over the southeast U.S. Another closed upper low will
move onshore the Pacific Northwest during the forecast period
while an area of disturbed weather and disorganized
showers/thunderstorms over the Bahamas will slowly drift westward
toward Florida by Day 3.

The latest model guidance is in above average agreement across the
northern tier of the US during the next 3 days with the evolution
of the upper level shortwave as it lifts northeastward into the
Hudson Bay area. A surface low deepening over the area is also
well represented and tightly clustered with the latest
deterministic guidance. In general, mass fields across the CONUS
are in good agreement such that a general model blend suffices.

The largest model variability exists with the tropical disturbance
near the Bahamas. Over the next 3 days, most of the global
deterministic guidance shows slow development. The 00Z GFS is a
faster and westward solution, with its low reaching Louisiana by
84 hours. Meanwhile, the UKMET is the furthest east, with its low
position near Jacksonville at 84 hours. The CMC/ECMWF offer a good
proxy for consensus at this time.


Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Friday, September 13, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
312 AM EDT Fri Sep 13 2019

Valid Sep 13/0000 UTC thru Sep 16/1200 UTC

00Z Model Evaluation with Preferences and Forecast Confidence

...Northern Plains/Upper Midwest Closed Low and Approaching
Shortwave...

Preference: General Model Blend
Confidence: Above average

A closed low currently over the northern Plains will lift
northeast and open up as it moves toward Ontario/Quebec this
weekend. Through 36 hours, there are only subtle differences in
the 500 mb heights and mass fields. A secondary shortwave behind
the main wave then approaches the northern tier of the U.S. and
southern Canada. The 00Z GFS is a bit deeper/amplified compared to
the rest of the guidance. Otherwise, guidance is in fairly good
agreement through the end of Day 3 and a general model blend is
preferred.


...Closed Low Approaching Pacific Northwest Day 3...

Preference: Non-UKMET blend
Confidence: Above average

07Z Update: The 00Z UKMET remains too fast with the digging trough
over the Pacific Northwest, especially by Day 3. The rest of the
models keep the trough axis offshore by the end of Day 3, while
the UKMET is solidly across the interior portions of OR/WA. With
this in mind, felt that it is too fast and should be excluded from
the blend, especially for Day 2/3.

---previous discussion---
A broad and strong closed low is expected to drop southeast from
the AK coast toward the Pacific Northwest by the end of Day 3.
There is above average support from the deterministic and ensemble
guidance with the evolution of this system such that a general
model blend of the available guidance is preferred at this time.
The 12Z UKMET is perhaps a tad faster than the rest of the
guidance but its differences are not significant enough to be
excluded at this time.


...Potential Tropical Cyclone Nine...

Preference: Official NHC Forecast
Confidence: Much below average

07Z Update: The rest of the 00Z guidance trended toward the east
similarly to the GFS/NAM, with pretty much all the guidance now
taking the low well off the FL/GA coastline by Day 3, although
there is considerable differences in terms of strength/intensity.
This is a below average forecast, particularly beyond 24-36 hours.

The latest official NHC track lies similar to a NAM/CMC/ECMWF
blend but users should see the official advisory for the latest
information regarding Potential Tropical Cyclone Nine.

---previous discussion---
See the latest official NHC advisory on Potential Tropical Cyclone
Nine.

Satellite imagery continues to show blossoming convective cloud
tops around Potential Tropical Cyclone 9 located over the
southeastern Bahamas. There is a growing consensus in the cyclone
developing into a Tropical Storm as it approaches the east coast
of Florida in the next couple of days. The track however remains
uncertain. The 00Z GFS did trend toward the other non-NCEP
guidance and shifted eastward, although it remains the western
outlier with its surface low moving toward Tampa and then turning
northeast toward Lake City. Meanwhile, the 12Z  UKMET/CMC/ECMWF
all remained off the east coast of FL, although with varying
degrees of intensity. A time trend analysis over the past 4 model
cycles show the GEFS members trending eastward toward the ECENS
and CMCE solutions. The 00Z NAM also offers some utility as its
track is fairly similar to the official. For now, based on the
latest advisory, the best proxy is a consensus of the ECENS/CMCE
with some inclusion of the NAM through Day 3.

Taylor

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Saturday, September 14, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
236 PM EDT Sat Sep 14 2019

Valid Sep 14/1200 UTC thru Sep 18/0000 UTC

12Z Model Evaluation with Preferences and Forecast Confidence

Preference: General Model Blend
Confidence: Above average

A very flat but tightly packed height pattern exists across the
CONUS, particularly the northern CONUS at the start of the
forecast period, with a subtle shortwave crossing ND into MN
today.  This wave will cross the Great Lakes and help to build
some broad troughing across the Northeast.  The 00z ECMWF is a bit
deeper than other guidance but with little significance
weather-wise to support the general model blend at above average
confidence.

...Deep Latitude Trof Entering the West by Monday; Southwest
shortwave...


Preference: 1/3rds 12z GFS & 2/3rds 12z ECMWF
Confidence: Average

19z update: The 12z UKMET slowed significantly but still remains
slightly faster than the remaining guidance, and with little
change in the ECMWF/CMC will keep initial preference of GFS/ECMWF
at average confidence.

---Prior Discussion---
GOES-WV suite denotes a nice outflow to the shortwave across the
Desert Southwest, this will move northward with similar evolution
in the guidance suite.  However, timing is going to be an issue
but this is mostly affected by the timing of the upstream digging
large scale trof entering N CA Monday.  There has been some
growing consensus with the UKMET/GFS slowing through Monday, but
typical of bias, by Tuesday the split in timing increases.  The
UKMET is well outpaced over the NAM/GFS followed by the lagging
ECMWF/CMC.  This appears to be a traditional timing issue, so a
typical GFS/ECMWF blend will likely work best with average
confidence
(given spread is moderate to large by Day 3). So
employing  a 1/3rd GFS and 2/3rds ECWMF solution works out well
here.


...Gulf of Mexico TUTT and Surface Wave...

Preference: 12z NAM/CMC/ECWMF blend
Confidence: Slightly above average

19z update: The 12z UKMET trended away from the stronger solution
and has become closer to the other guidance, but is a bit further
north and faster to keep included.  The 12z CMC trended faster and
matches tightly with the 12z NAM/ECMWF to suggest the GFS is now a
bit too fast as well, so will favor a 12z NAM/ECMWF/CMC blend.

---Prior Discussion---
The TUTT cell moving west across the Gulf continues to look
impressive with a solid trailing surface wave.  The 12z NAM and
ECMWF are very similar in depth and timing of both features, while
the GFS is in a semi-biased weaker phase relative to both but
timed well.  The 00z UKMET is typical bias in tropical systems
with strong convective response leading to a compact wave that
feeds back on itself...slowing and shifting north of the remaining
guidance.  The 00z CMC evolves the surface wave well, but the TUTT
is a bit too weak and slow, so the surface wave lags.  So while
not favored in a blend, it does provide confidence to the
evolution of the system.  So a 12z NAM/GFS and 00z ECMWF blend is
preferred in the Gulf at slightly above average confidence.


...Tropical Storm Humberto...

Preference: Official NHC Forecast
Best Proxy: 12z CMC/ECMWF through 48hrs; 12z GFS/NAM thereafter
Confidence: Average

19z update: The 12z ECMWF/CMC track quite close to the 15z NHC
forecast through 48hrs, thereafter the CMC and ECMWF slow
significantly with the NAM/GFS passing it along the NHC track.
The UKMET is the only guidance member faster than NHC forecast
track but remains very strong comparatively as well.  So the best
proxy will be the CMC/ECWMF through 48hrs and more GFS/NAM
thereafter.

---Prior Discussion---
Humberto is starting to have a stronger/deeper appearance at this
time.  There remains a solid split in the guidance with the
ECMWF/UKMET continuing to be east and eventually south of the NHC
track after the turn at 36 to 48hrs.  The 12z GFS/NAM both start
initially slower and slightly east of the 00z guidance but still
are west and northwest over the next two days before turning east.
 The 00z CMC is closest to the track through 48hrs before
accelerating after the eastward turn...moving away from the other
guidance.  It is at this point the GFS/NAM both move along the
eastward track after 48hrs with better timing, perhaps a bit slow.
 Overall, the best proxy in a general model blend, but to not
blend out the features too much; a 00z CMC through 48hrs shifting
to GFS/NAM thereafter works closest to the NHC forecast.  There is
growing consensus as the guidance envelope tightens, as such
confidence is average in utilizing this proxy for the 15z NHC
forecast.

Gallina

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Sunday, September 15, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1256 AM EDT Sun Sep 15 2019

Valid Sep 15/0000 UTC thru Sep 18/1200 UTC

00Z Model Evaluation with Preferences and Forecast Confidence

...Deep Latitude Trof Entering the West by Monday; Southwest
shortwave...

Preference: General Model Blend Day 1/2; Non-UKMET blend Day 3
Confidence: Average

Deepening trough over the western U.S. through the period will
eject a shortwave trough into the Rockies and Northern Plains by
Day 3. The latest round of models have come into better agreement
with its depth and orientation as it moves on shore such that a
general model blend can be applied for Day 1/2. For Day 3, a
shortwave will round the trough and lift into the northern Rockies
and Northern Plains. The UKMET continues to be too fast compared
to the rest of the guidance. By the end of Day 3, the system is
expected to deepen somewhat (which all the models do), but the
GFS/NAM are much stronger compared to the ECMWF/CMC. Finally,
another closed low is then expected to drop into the Pacific
Northwest, and here model differences are quite high. The best
agreement at this time seems to be with the ECMWF/GFS/NAM.


...Tropical Storm Humberto...

Preference: Official NHC Forecast
Best Proxy: General model blend through 24 hours; GFS/NAM blend
after

Confidence: Average

Humberto continues to exhibit signs of strengthening per recent IR
imagery showing convective bursts near the center, though most of
this is displaced to the northern half of the system. Its forward
direction is generally north/northwest at about 5 kt, per the
latest NHC advisory. In the next 24 hours, Humberto is expected on
this general direction before making a turn to the northeast after
36 hours. The latest guidance is tightly clustered through 24
hours, with the GFS/NAM left of the center while the non-NCEP
guidance slightly to the right of the official track. Differences
increase beyond 24-36 hours, with respect to how quickly the
system turns northeast and to what degree. The GFS/NAM suggest a
slower/more gradual turn while the ECMWF is slower but further to
the right. Meanwhile, the UKMET while initially to the right of
the track, then takes a more northerly turn. At 84 hours, the
official point lies near the consensus, but the spread is
considerable between the various deterministic models.

Taylor

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Monday, September 16, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
334 AM EDT Mon Sep 16 2019

Valid Sep 16/0000 UTC thru Sep 19/1200 UTC

00Z Model Evaluation with Preferences and Forecast Confidence

...Deep Latitude Western Trof Entering the West; Reinforced by
Closed Low Late Tues...

Preference: General Model Blend
Confidence: Slightly above average

07Z Update: Earlier issues with the 12Z CMC seem to have been
resolved with the 00Z run, such that a general model blend is
preferred.

---previous discussion---
Fairly good agreement in the latest model guidance that a pair of
shortwaves will work through the Pacific Northwest and into the
northern Rockies and northern Plains during the forecast period.
First shortwave that is currently moving onshore the west coast
will rotate quickly into Montana and North Dakota by Day 2. Here,
earlier discrepancies between the UKMET and the rest of the
guidance with respect to the speed have mostly been resolved. The
UKMET might remain a bit faster than the others, but a general
model blend should provide a reasonable solution. The secondary
shortwave that then drops into the Pacific Northwest by Day 2/3 is
fairly agreed on. The one exception would be the 12Z CMC, which is
too far south and amplified with the closed low, as it takes it
into northern California. Meanwhile, the rest of the guidance is
north across Oregon and more positively titled.


...Southwest Shortwave, Moving through Central High Plains into
Northern Plains/MN by Tuesday...


Preference: General model blend through 48 hours; non-GFS through
84 hours

Confidence: Slightly above average

07Z Update: With the initial shortwave rounding the base of the
trough on Day 2, agreement is pretty good with the latest model
guidance. As the shortwave approaches the northern Plains, the GFS
comes out too fast and while the UKMET and NAM are a bit too deep,
its position agrees well with the 00Z ECMWF/CMC. As such, less
weight is given to the GFS for Day 3.

---previous discussion---
Weak shortwave over the Four Corners region currently seen in
water vapor imagery will continue to drift north/northeast over
the forecast period and gradually become absorbed into the large
scale troughing over the western US. The shortwave is expected to
reach the central Plains late Monday and then into the northern
Plains and Upper Midwest by Tuesday. The various deterministic
models offer fairly similar solutions with just slightly varying
degrees of strength and timing (CMC a bit fast; ECMWF
slower/west). Overall, a general model blend is preferred.


...Gulf of Mexico Tropical Wave...

Preference: 2/3rd UKMET, 1/3rd GFS blend
Confidence: Average to Slightly Below Average

Guidance has come into better agreement that a weak surface wave
moving westward over the central/western Gulf of Mexico will
gradually take on better organization in the next few days as it
approaches the Texas Gulf Coast. The system is expected to produce
locally heavy rainfall somewhere along the coast by Day 3.
Guidance has some latitudinal differences but for now, a consensus
of the GFS and UKMET (with more inclusion of the UKMET by Day 3)
is preferred. Forecast confidence is average at first, then drops
to slightly below average by Day 3.


...Hurricane Humberto...

Preference: Official NHC Forecast
Best Proxy: GFS/ECMWF
Confidence: Below Average

07Z Update: The latest ECMWF, along with the GFS, are the best
proxies for the latest official NHC track. The UKMET and NAM
continue to be too fast and the CMC, while not bad in the first
24-36 hours, is considerably slower and to the right of the track
beyond that period.

---previous discussion---
Hurricane Humberto continues to strengthen given warm waters and
favorable environmental conditions. Its slow motion has taken a
gradual north/northeast direction and this is expected over the
next several days. The latest guidance is in reasonable agreement
with the official NHC advisory track through about 24-36 hours,
but beyond that, there is sizable spread in the latest model
guidance. The NAM and UKMET are the faster solutions, as Humberto
gets picked up in the approaching mid-latitude trough earlier.
Meanwhile, the CMC/ECMWF stall the system much longer and
therefore are the slowest and further south solutions by Day 3.
For this cycle, the GFS is the best proxy for the track through
the entire forecast period, although there remains some deviations
from the latest official NHC track. In general, forecast
confidence drops off considerably beyond 36-48 hours.

Taylor


Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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Wednesday, September 18, 2019

Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1236 AM EDT Wed Sep 18 2019

Valid Sep 18/0000 UTC thru Sep 21/1200 UTC

00Z Model Evaluation with Preferences and Forecast Confidence

Preference: Model blend weighted toward ensemble means
            ECMWF Ensemble and GEFS Ensemble greatest weight

Confidence: Average

Through the next 3 days, the synoptic pattern is expected to
feature troughing over the western U.S. with a persistent ridge
anchored over the southeast U.S. By the end of Day 3, the trough
axis moves into the central and northern Plains. The deterministic
model heights at 500 mb are tightly clustered and well within the
ensemble means. The model preference and blends will be anchored
by greater weight placed on the ensemble means, specifically the
ECMWF ensemble and GEFS ensemble. These were also used to trend
the timing of the rainfall associated with Tropical Depression
Imelda in Texas.

Taylor

Model Diagnostic Discussion
Preferred Height Pattern
500 mb Height Trends
Forecast issued by the Weather Prediction Center

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