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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
238 AM EDT Mon Oct 21 2019

Valid 12Z Thu Oct 24 2019 - 12Z Mon Oct 28 2019

Guidance/Uncertainty Assessment and Weather Highlights/Threats:

Guidance agrees that the active flow pattern will reload over the
cooling/unsettled West Wed/Thu as digging upper impulse/jet
energies support some enhanced Rockies snows. Height falls should
then act to carve out an amplified central U.S. upper trough later
week.
Pattern evolution uncertainty grows quickly, resulting in
low forecast confidence.
Guidance continues to indicate two
possible scenarios by this weekend:

  • (1) A more amplified upper trough draws in deep moisture from the Gulf and results in a low pressure system that spreads heavy rainfall well inland, as indicated by recent ECMWF/UKMET and CMC solutions; or
  • (2) less flow separation between the northern and southern streams will keep a cold front moving steadily across the southern and eastern U.S., as indicated by recent GFS runs.
     

GEFS/EC/CMC ensembles are mixed, with ECMWF ensembles showing
the most support for the first scenario. WPC progs modestly lean the
forecast to show such potential.
This considers upstream upper ridge
amplitude and as the next main upper trough does not bring renewed cooling with
enhanced precipitation/mountain snows through the Northwest then
Rockies until next weekend, so wavelength spacing with the
downstream system seems sufficient to allow for at least some
southern stream separation.

Schichtel

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
313 AM EDT Tue Oct 22 2019

Valid 12Z Fri Oct 25 2019 - 12Z Tue Oct 29 2019

Guidance/Uncertainty Assessment and Weather Highlights/Threats:

Models and ensembles continue to show quite varied medium range
solutions that mainly stem from the extent of short range
shortwave digging down through the w-central U.S. and subsequent
southern stream flow separation. Forecast confidence is not
stellar.

Recent ECMWF and to a slightly lesser extent ECMWF ensemble mean
and Canadian/Canadian ensembles and to some extent the UKMET
continue to show max digging within the full envelope of
solutions. This leads to the most separated southern stream and
most westward/amplified closed low development and slowest/wettest
subsequent northeastward system track over the central then
eastern U.S. at medium range time scales as a new upstream upper
trough amplifies sharply back over the West and upper ridging
builds over the Southeast.
Recent GFS and to a lesser extent GEFS
runs instead show the least short range digging over the West that
subsequently offers much less downstream southern stream
separation, no closed low development, and way more progressive
and eastward flow over the central to eastern U.S. that offers a
significantly less heavy rainfall threat.

Still suspect that the sharp upper ridge amplitude building into
the West coast over the next couple of days and sufficient
wavelength spacing from subsequent upstream upper trough approach
from the Pacific should favor a solution well on the more
amplified and southern stream/closed low separated side of the
aforementioned full envelope of guidance solutions
. Given the
GFS/GEFS have not trended significantly in that direction with the
latest 00 UTC runs, opted to not jump all the way to the ECMWF at
this point given lingering uncertainty. However, suggest
preference of the still stormy ECMWF ensemble mean and the
Canadian/Canadian ensemble mean that were primarily used as a
starting point for the WPC medium range product suite. This
solution offers a threat of widespread heavy rainfall/convection
centered over the South Fri into the weekend from the main lead
system
and substantial cooling upstream over the West/Rockies to
include a threat of heavy mountain snows to occur by early next
week upper trough amplification.

Schichtel

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
306 AM EDT Thu Oct 24 2019

Valid 12Z Sun Oct 27 2019 - 12Z Thu Oct 31 2019

Overview and Guidance/Uncertainty Assessment:

Model spread remains significant during the extended period in an
active pattern.
For the last week or so the GFS has been
consistently too progressive with energy tracking across the
CONUS. This seems to be the case with the latest GFS runs and
GEFS/NAEFS means are also in this camp to a lesser extent. Recent
UKMET and especially Canadian runs have been closer to the ECWMF
and the ECMWF ensemble mean and offer a deeper and slower
progression of the low/trough exiting to the eastern U.S. by early
next week and amplifying upstream upper troughing digging into the
West then w-central U.S. next week. Accordingly, the WPC medium
range product suite was primarily derived from a composite blend
of the best clustered solutions from the ECMWF/Canadian and ECMWF
ensemble mean, with highest weighting applied to the ensemble mean
for max continuity amid uncertainty.

Weather Highlights/Threats:

The resultant weather pattern may offer several significant
hazards.
Lead system ejection over the eastern U.S. Sunday and a
wavy trailing front over the Southeast into early-mid next week
should act to focus precipitation. Rainfall may be enhanced with
potential entrainment of tropical moisture stemming from a
tropical disturbance that the NHC is monitoring over the Gulf of
Mexico.

Meanwhile upstream, the deep digging of a series of potent systems
favors an unsettled and cooled West then central U.S. next week
with advent of a series of post-frontal high pressure surges. Some
upwards of 15-30+ degree negative temperature anomalies may rival
record values and upper support/modest moisture sets the stage for
terrain enhanced snows over the West and especially the central
Rockies with potential likely spreading northeast over the central
Plains then Upper Midwest with gradual system progressions and
cooling. Lead heavier rains may also be re-develop along/ahead of
a reinforced low/frontal boundary with renewed return moisture
influx from the Gulf of Mexico over the east-central U.S.
mid-later next week.

Schichtel

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Sun Oct 27 2019

Valid 12Z Wed Oct 30 2019 - 12Z Sun Nov 03 2019

 

  • Much below normal temperatures over the West/Plains as of Wed will gradually moderate
  • Developing storm likely to affect the eastern half of the country during the latter half of the week
     

Overview and Guidance/Uncertainty Assessment:
Guidance still shows some broadening of the eastern Pacific mean
ridge aloft over the course of the period, ultimately leading to a
neutrally tilted mean trough settling into the east-central U.S.
in contrast to the positively tilted trough extending into the
West early-mid week.  While some spread persists for the
specifics, there is a steadily improving signal that the last
significant bundle of energy aloft ejecting from the West will
generate a deepening storm system around Thu-Fri.  The surface low
should track from the Mississippi Valley/Ohio Valley
north-northeast through the Great Lakes into southern Canada and
be accompanied by a broad shield of various precipitation types.
Depending on how much the storm deepens, strong winds will also be
possible as it reaches/passes the Great Lakes.  Expect much of the
lower 48 to be fairly dry after this storm departs.

Maintaining fairly good continuity, the updated forecast
emphasized the 12Z ECMWF/UKMET/CMC during the first half of the
period.  Then the forecast steadily increased 12Z ECMWF mean input
toward half weight while holding onto some aspects of the 12Z
ECMWF/CMC (plus adding the prior 00Z ECMWF run to account for
increasing detail uncertainty).

The GFS has been trending slower with the upper low ejecting from
the central Rockies but continues to be on the faster side of the
spread.  Recent verification and trends have steadily favored the
slower majority cluster of guidance.  Interestingly the past
couple GEFS mean runs have aligned quite well with the ECMWF
cluster aloft for Wed-Thu but become more open than consensus
thereafter.  The new 00Z CMC evolves to an open wave aloft as well
but remaining models maintain an upper low and in fact become
deeper and more concentrated as the system reaches the Great Lakes
by Fri.  However a weaker trend in recent ECMWF runs does temper
confidence in the deepest GFS/UKMET solutions.

Behind this system there is decent agreement that cyclonic flow
aloft will bring one cold front into the northern tier by Fri
(weakening by Sat) with another front approaching by Sun.  By next
weekend guidance differences are fairly modest outside of details
that have low predictability at the days 6-7 time frame,
supporting a model/ensemble mean blend.  Recent GEFS means have
tended to be on the weaker side of the spread for the eastern
Pacific ridge aloft so that solution was excluded from the blend.
The new 00Z GEFS mean seems to have trended in a favorable
direction though.


Weather Highlights/Threats:
The dominant weather focus during the period will be the upper low
expected to track from the central Rockies through the Great Lakes
and into Canada, with deepening low pressure lifting through the
east-central U.S. Thu-Fri.  The best potential for meaningful snow
in the cold sector should extend from the central Rockies/Plains
northeast into the Upper Great Lakes.  Ahead of the storm expect a
broad area of rainfall and possibly considerable coverage of heavy
amounts.  Activity may be enhanced by an area of moisture
currently over the Caribbean and expected to lift northward across

the Gulf of Mexico into the southern states.  Some embedded
convection could be strong as well.  There may be a period of
brisk to strong winds over the Great Lakes/Northeast as the
deepening surface low reaches and departs from the Great Lakes.
Behind this system expect much of the lower 48 to be dry, aside
from some lake effect rain/snow and scattered light precipitation
with fronts affecting the northern tier as well as mostly light
rainfall along the front settling over the Florida Peninsula.

The central Rockies/Plains will be in the core of coldest air
around midweek with some locations seeing highs 30-40F below

normal.  A much broader area from the Interior West through
central U.S. will see temperatures at least 10-20F below normal.
Some daily records for lows/cold highs are likely.  Readings will
trend warmer from late week into the weekend over the West and
into the Plains, with the eastern Pacific upper ridge possibly
nudging far enough eastward to bring modestly above normal
temperatures to the West Coast states by the weekend.  Meanwhile
the East will see a cooling trend by the weekend after warm/moist
flow leads to a couple days or so of plus 10-20F anomalies for
morning lows mid-late week.  The cool anomalies over the East by
the the weekend will be much less extreme than those forecast
farther west early in the period.


Rausch

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Mon Oct 28 2019

Valid 12Z Thu Oct 31 2019 - 12Z Mon Nov 04 2019

  • Much below normal temperatures over the Rockies/Plains will gradually moderate
  • Developing storm likely to affect the eastern U.S. Thu-Fri

Overview and Guidance/Uncertainty Assessment:

Models and ensemble means agree that a persistent eastern Pacific
ridge will promote broad cyclonic flow downstream, with a mean
trough axis tending to align over the east-central states.
Guidance consensus and continuity provide fairly high confidence
in the large scale pattern but individual embedded features have
lower predictability.  By early next week there are also some
aspects to the forecast that become more uncertain near the West
Coast and into western Canada.

In terms of sensible weather effects the greatest forecast problem
continues to involve the upper trough expected to be over the
central U.S. as of early Thu and eject northeastward thereafter,
supporting development of surface low pressure that tracks from
near the Ohio Valley northeastward into eastern Canada.  Over the
past day there has been some notable trending in the guidance as a
whole toward faster progression (likely due in part to a stronger
trailing upper trough dropping southeastward from Canada) and a
weakening of the surface low among the prior strongest solutions
(some ECMWF/GFS/UKMET runs).  
The past couple CMC runs are in the
minority with a more phased/open system aloft leading a faster and
less wound-up wave.  Spread and trends in the guidance as well
less than usual clustering among individual ensemble members for
the time frame involved keep confidence in any specific solution
lower than average.
 Based on guidance available through the 18Z
cycle the updated forecast was based on a blend among the 12Z and
00Z/27 ECMWF runs along with the 18Z GFS and 12Z UKMET.  This
solution kept GFS weight low enough to yield minimal influence on
day 3 Thu when that model is farther south and/or east than most
other guidance aloft.  After that time the GFS fell more in line,
and in fact was slower than the ECMWF/ECMWF mean by early Fri.  By
Fri some of the new 00Z guidance continues to trim away the
western/slower side of the prior model envelope for the surface
low--but in a significant exception the 00Z ECMWF has adjusted
slower.  At that time the manual forecast falls between the new
and previous ECMWF runs.

Behind the eastern system the aforementioned model blend
represented consensus well for the upstream trough aloft
amplifying into the lower 48 along with the associated cold front
which should weaken by Sat.  Given the time frame involved there
is decent agreement and consistency with the next frontal system
expected to reach the northern tier/Great Lakes by days 6-7
Sun-Mon.  The scale and progression of shortwave energy aloft
suggest there could be more variability in future runs though.
Late in the period GFS/GEFS mean runs develop lower heights aloft
near/offshore California than most other guidance.  In addition
the GEFS mean remains among the weakest guidance with the Pacific
ridge and the 12-18Z GFS runs gradually shifted the ridge-trough
pattern a little east of consensus (while the 00Z GFS looks better
in that regard).  As a result the forecast adjusted toward primary
emphasis of recent ECMWF runs and the 12Z ECMWF mean.  The 18Z
GEFS mean did compare acceptably for the overall North America
trough to merit a small minority weight in the forecast.


Weather Highlights/Threats:

Confidence remains lower than desired for exact details of the
developing system likely to track from the Ohio Valley through the
eastern Great Lakes and into eastern Canada during Thu-Fri.

However there is still a common theme of a widespread
precipitation shield across the eastern U.S.
with some snow
possible in the northwestern periphery of the system (Midwest to
Upper Great Lakes) and areas of heavy rainfall along with pockets
of strong convection in the warm sector.  Currently expect highest
rainfall totals from early Thu onward to extend from along and
just west of the Appalachians into the Northeast.
 A brief period
of fairly strong winds will be possible over parts of the Great
Lakes/Northeast but details will require better agreement on the
depth/track of the surface low.  Behind this system expect periods
of lake effect rain/snow with periodic light precipitation over
other parts of the northern tier in association with a couple
fronts dropping south from Canada.  The front trailing from the
late week eastern storm will settle over the Florida Peninsula and
could provide a focus for light rain into early next week.

The Rockies and Plains will remain quite chilly into late week
with a fairly broad area seeing temperatures 10-30F below normal.
These areas should trend much closer to average by Sun-Mon while
locations closer to the West Coast should see highs up to 5-10F
above normal from the weekend onward as the Pacific ridge aloft
extends its influence a little farther eastward.  Meanwhile
frontal passage over the East will replace initial warmth (plus
10-20F anomalies for morning lows and moderately warm highs on
Thu) with cooler readings generally 5-15F below normal.

Rausch

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Tue Oct 29 2019

Valid 12Z Fri Nov 01 2019 - 12Z Tue Nov 05 2019

Overview and Guidance/Uncertainty Assessment:

Latest models and ensemble means continue to show an amplified
pattern whose large scale tends to yield better than average
predictability, featuring a northeastern Pacific ridge and
downstream trough whose multi-day average axis should be over
east-central North America.  In contrast to the short-range system
affecting the lower 48 and forecast to be over southeastern
Canada/New England as of early Fri--which has been plagued by high
spread and variability in the guidance for multiple
days--solutions cluster remarkably well in most respects through
the middle of the extended period.  Not surprisingly shortwave
details become more uncertain toward days 6-7 Mon-Tue.

Based on guidance through the 18Z cycle, a blend of the 18Z GFS
and 12Z ECMWF/UKMET provided a good representation of the system
near New England early Fri with a position near an average of the
18Z GEFS/12Z ECMWF means.  Review the Model Diagnostics Discussion
PMDHMD for updated model preferences incorporating the new 00Z
guidance in the short range time frame through 12Z Fri.  Behind
this system the aforementioned blend also reflected consensus for
a couple upstream features, a central/eastern U.S. front with
anchoring surface low tracking over southern Canada/Lake Superior
and an upstream wave reaching just north of the northern Plains by
early day 5 Sun.  The rest of the forecast trended toward an even
model/mean blend consisting of the 18Z GFS/12Z ECMWF and their
ensemble means, with model details beginning to diverge somewhat
but still in the proverbial ballpark relative to the GEFS/ECMWF
means that were quite similar to each other through day 7 Tue.
This solution would have the southern Canada wave on Sun track
over/near the Upper Great Lakes Mon and northeast thereafter while
the trailing front pushes into the central U.S. in a fashion
similar to the Fri-Sat front.

The relative agreement of the GEFS/ECMWF means conceals some of
the individual member spread that becomes evident over the
northwestern U.S. and western Canada toward the end of the period.
 The spread becomes more dramatic when adding in some CMC
ensembles that develop more troughing than most GEFS/ECMWF
members.  Over the past couple days the multi-day means by D+8
have been differing over exactly where the strongest positive
height anomaly center(s) will be within an area covering the
northeastern Pacific/Gulf of Alaska through the eastern Bering
Sea.  These differences lower confidence in determining exactly
how shortwaves rounding the ridge may amplify downstream late in
the period and beyond.

Along and offshore the California coast there is a converging
trend regarding potential for a weak upper low, whether from one
individual feature or consolidation of multiple impulses.
GFS/GEFS runs are still somewhat deeper than other guidance but an
even blend between them and the ECMWF/ECMWF mean is reasonable
given some recent trends toward the GFS idea in principle.


Weather Highlights/Threats:

The East will see a rapid drying trend while brisk to strong winds
over the Northeast on Fri will slacken as low pressure lifts
northeastward away from New England.  Northern tier areas will see
periods of mostly light rain and/or snow with a couple
waves/frontal passages, including some enhancement to the lee of
the Great Lakes.  Specifics become more uncertain after this
weekend.  The front extending south from the departing Fri system
will settle over the Florida Peninsula, providing some focus for
occasional rain (mostly light) as easterly low level flow becomes
established.

Some areas over the Rockies and Plains will see temperatures
10-20F or so below normal Fri-Sat followed by readings closer to
normal.  Another front dropping south from Canada may bring
modestly below normal temperatures during the first half of next
week.  Meanwhile during the weekend a modified form of the chilly
Plains air will reach the East with highs/lows generally 5-15F
below average.  Eastern areas should return close to normal by
Mon-Tue.  The West will see a gradual increase in coverage of
above normal highs but with anomalies tending to be around plus
10F or less.

Rausch

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EDT Wed Oct 30 2019

Valid 12Z Sat Nov 02 2019 - 12Z Wed Nov 06 2019

Overview and Guidance/Uncertainty Assessment:

Most guidance maintains good agreement and continuity with the
expectation of a persistent and fairly amplified east-central U.S.
mean trough downstream from a northeastern Pacific ridge.  There
has been some typical spread/variability with details, which
favors maintaining a model/ensemble mean approach to represent the
most common ideas of guidance while downplaying less confident
specifics.

Within the forecast mean pattern expect a leading shortwave over
the Mississippi Valley early day 3 Sat to lift northeastward
during the weekend and push a leading cold front through the East.
 Upstream shortwave energy over southern mainland Alaska and the
Gulf of Alaska on Sat will quickly drop southeast and support a
northern tier surface low and trailing front late weekend into
early next week.  The primary consideration for this feature is
that recent GFS runs (including the new 00Z run) carry their
surface wave slower and farther south than the majority cluster
that consists of the ECMWF/UKMET and the ensemble means.  The CMC
is on the weaker side of the spectrum but the low track in the 00Z
run is close to consensus as well.  An operational model blend to
start the period and then by day 5 Mon adding some 18Z GEFS/12Z
ECMWF mean input and reducing the 12Z/18Z GFS a bit reflects
consensus early and a non-GFS solution for the early week northern
tier system.

Later in the period the GEFS/ECMWF means have been very agreeable
and stable at least for their mass fields.  Thus prefer to trend
the more distant part of the forecast 50-60 percent in their
direction.  The 12Z ECMWF compared better to the means than the
18Z GFS in particular, though the new 00Z GFS has trended
favorably into early Wed.  As a result the late-period operational
component used more 12Z ECMWF than 12Z GFS while phasing out the
18Z run.  This solution brings the next upper trough into the East
by next Wed with the leading front reaching the East Coast by
then.  The greater model/ensemble discrepancy involves moisture
return ahead of the late-period eastern front.  Localized ECMWF
precip amounts and ECMWF mean coverage could be a little
aggressive but consensus suggests that GFS runs could be too fast
with southern stream energy that could play a role in developing
at least some areas of rain.

As suggested by variability in recent operational model runs,
there is still a fair degree of uncertainty over wave details
along the mean frontal boundary likely extending from southwest
Canada southeastward into the Rockies/High Plains.  This is
connected to various potential solutions for what happens with
shortwave energy expected to be over Alaska/northwestern Canada
early in the week.  Thus far GEFS/ECMWF ensembles are narrowing
their spread toward keeping the northeast Pacific ridge rather
strong and not allowing the shortwave energy to elongate westward
like the 18Z GFS and to some degree 12Z GFS.  On the other hand
CMC ensembles continue to show lower heights over the northwestern
states--seemingly a low probability scenario at this time given
the robust consensus of the GEFS/ECMWF means and operational
GFS/ECMWF/CMC runs.  Finally, GFS/ECMWF runs and their means have
come into good agreement for the weak upper low offshore
California.


Weather Highlights/Threats:

From the weekend into the start of next week the majority of
precipitation will be with areas of mostly light-moderate snow and
rain between the northern Rockies/High Plains and Great Lakes.
Cool cyclonic flow around a leading system tracking away from the
Upper Great Lakes will promote a period of lake effect activity
while the next wave tracking into the northern tier and trailing
front will provide another precipitation focus.  From Mon into Wed
the passage of the northern wave will generate more precipitation
over the Great Lakes with lower confidence in precip coverage to
the west.  Rainfall coverage may increase somewhat over the
eastern half of the country as the northern tier system's front
heads toward the East Coast, but to what extent remains uncertain
and dependent on evolution/timing of upper dynamics.  One other
localized area of rainfall during the period will be over the
Florida Peninsula in association with a stalling front and
easterly low level flow.

The eastern periphery of the Pacific ridge aloft will provide
modestly warm temperatures to most of the West during the period,
with most anomalies for highs around plus 10F or less.  One chilly
airmass will progress across the central/eastern states during the
weekend with most locations seeing at least one day with highs
10-20F below normal.  Well below normal anomalies should be less
extensive with the next push of cool air Mon-Wed, with areas from
the northern High Plains into the Upper Midwest/Great Lakes most
likely to see highs 10-20F below normal.

Rausch
 

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
221 AM EDT Fri Nov 01 2019

Valid 12Z Mon Nov 04 2019 - 12Z Fri Nov 08 2019

Pattern Overview/Weather Threats and Guidance Assessment:

Broad cyclonic flow aloft will dominate much of the lower 48 next
week as a series of impulses reinforce a central North American
mean upper longwave trough. This trough may gradually shift
eastward as east Pacific upper ridging grudgingly work into a dry
West Coast. The pattern will favor the spread and periodic
reinforcement with colder than normal air masses from the Rockies
and Central U.S. to the East as post-frontal high pressure cells
spill down from Canada. Moisture will be mainly limited across the
mid-higher latitudes, but the passage of several clipper lows
should support modest snow/rain swaths over the U.S. northern tier
from the Rockies through the Great Lakes/Northeast where activity
will be prolonged by lake effect. Moisture may sufficiently feed
into/over a wavy lead front to fuel some moderate rains for FL and
the coastal Southeast/Carolinas early next week, then back over
the southern Plains mid-later next week where cooled temperatures
offer some risk of a light icy coating on the far northern
periphery of return flow with secondary frontal passages.

The WPC medium range product suite was primarily derived from a
composite blend of the quite compatible latest GEFS/ECMWF ensemble
means in lue of reliance on deterministic models that show more
run to run continuity issues with the timings/amplitudes of
embedded weather systems.

Schichtel

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
130 AM EST Sun Nov 03 2019

Valid 12Z Wed Nov 06 2019 - 12Z Sun Nov 10 2019

Pattern Overview and Guidance/Predictability Assessment:

The large scale pattern across the CONUS shows above average
predictability during the medium range.
A building ridge from the
northeastern Pacific north to Alaska and British Columbia will
favor a mean upper trough downstream over the east-central U.S.

The main difference among the guidance becomes evident Thu into
next weekend with respect to a potential wave of low pressure
along the surface front across the Ohio Valley/Appalachians to off
the Northeast U.S. coast. Guidance has trended over the past 24
hours toward a more significant wave of low pressure, as shown by
the ECMWF/CMC
. The GFS/UMKET, on the other hand, moves any
potential weak wave of low pressure eastward and well offshore
much more quickly. There is an increasing number of ECMWF/Canadian
and even GEFS ensemble members supporting a solution more in line
with the ECMWF/CMC. This solution keeps better WPC continuity and
seems more plausible considering favorable upstream ridge
amplitude and baroclinic/dynamic environment to feed upon for
development. However, confidence in this aspect of the forecast is
not high considering the short wavelength spacing between the
progressive impulses embedded with the larger scale flow that dig
and carve out the e-central U.S. upper trough from a distant
source region over northeast Asia and the Arctic/Alaska.

Overall, the WPC medium range forecast was primarily derived from
a blend of the 12 UTC ECMWF/Canadian/ECMWF ensemble mean and the
18 UTC GEFS ensemble mean.

Weather Highlights/Threats:

Expect mainly dry conditions for much of the West except until
late week as Pacific moisture breaks inland into Pacific Northwest
terrain. The downstream pattern will favor the spread and periodic
reinforcement with colder than normal air masses from the Rockies
and Central U.S. to the East as post-frontal high pressure cells
spill down from Canada.
High temperatures are forecast to be as
much as 10-20 deg F below average across much of the central and
eastern U.S. next week as the strong Canadian high pressure moves
southward into the U.S. Moisture will be mainly limited across the
mid-higher latitudes, but the passage of several clipper lows
should support mainly snows swaths over the cooled U.S. northern
tier from the Rockies through the Great Lakes/Northeast where
activity will be prolonged by lake effect. Recent guidance trends
show an increasing signal for overrunning precipitation north of a
surface front across the Southern Plains Wed into Thu, with the
potential for a couple inches of rainfall. Strong high pressure
and cold temperature well north of the surface front, from the
central Plains and Mid-Mississippi Valley to the Ohio Valley and
Northeast, could result in a risk of wintry precipitation whose
threat would be enhanced with aforementioned organized frontal
then coastal low development.

Schichtel/Ryan

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
137 AM EST Mon Nov 04 2019

Valid 12Z Thu Nov 07 2019 - 12Z Mon Nov 11 2019

Pattern Overview and Guidance/Predictability Assessment:

The large scale pattern across the CONUS shows above average
predictability during the medium range. An amplified ridge from
the northeastern Pacific to Alaska and British Columbia will favor
a mean upper trough downstream over the east-central U.S.

It remains the case that the main guidance difference becomes
evident Thu into Sat with a potential wave of low pressure along
the surface front across the OH Valley/Appalachians to off the
Northeast U.S. Differences hinge largely in the timing of a
shortwave crossing the Upper Midwest/Great Lakes/Northeast
Thu-Fri. Guidance is still divided into two camps surrounding this
feature, with recent ECMWF/CMC runs slower and deeper with the
shortwave and recent GFS/UKMET runs faster. The slower solutions
develop a more significant wave off the Eastern Seaboard whereas
the faster solutions move the front out to sea quickly. Another
notable differences in the GFS was that the trailing end of the
front interacts with a stronger southern stream impulse, causing a
wave of low pressure to develop across the Southeast Thu night-Fri
night. Based on an assessment of ensembles and run-to-run
consistency, still opt to go more toward the ECMWF/CMC scenario
that actually has reasonable GEFS support. This idea keeps better
WPC continuity and seems more plausible considering favorable
upstream ridge amplitude and baroclinic/dynamic environment to
feed upon for development. However, confidence in this aspect of
the forecast is not high considering short wavelength spacing
between the progressive impulses embedded in the large scale flow
that dig and carve out the e-central U.S. upper trough from a
distant Arctic/Alaska source region.

By the end of the forecast period late in the week, a relatively
strong North Pacific flow regime should persist, with forecast
confidence in the timing of specific shortwaves reaching the CONUS
relatively low despite somewhat above average consensus on the
large scale pattern.

Overall, the WPC forecast was based mainly on the ECMWF/CMC and
GEFS/ECENS ensembles.


Weather Highlights/Threats:

Expect mainly dry conditions for much of the West except until
late week as Pacific moisture spreads inland into Pacific
Northwest terrain. The downstream pattern will favor the spread
and periodic reinforcement with colder than normal air masses from
the Rockies and Central U.S. to the East as post-frontal high
pressure cells spill down from Canada. High temperatures are
forecast to be as much as 10-20 deg F below average across much of
the central and eastern U.S. at times as the strong Canadian high
pressure moves southward into the U.S.
Moisture will be mainly
limited across the mid-higher latitudes, but the passage of
several clipper lows should support mainly snows swaths over the
cooled U.S. northern tier from the Rockies through the Great
Lakes/Northeast where activity will be prolonged by lake effect.
There remains a signal for overrunning precipitation north of a
surface front across the Southern Plains and lower MS Valley Thu,
with the potential for a couple inches of rainfall, with more
modest activity spreading quickly northeastward Fri. Strong high
pressure and cold temperature well north of the surface front,
from the central Plains and Mid-Mississippi Valley to the Ohio
Valley and Northeast, could result in a risk of wintry
precipitation whose threat would be enhanced with aforementioned
organized frontal then potential coastal low development. This
threat continues to be shown in recent WPC Winter Weather Outlook
probabilities.

Schichtel/Ryan

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
158 AM EST Tue Nov 05 2019

Valid 12Z Fri Nov 08 2019 - 12Z Tue Nov 12 2019

  • New England coastal storm and heavy snow threat Friday
  • Multiple cold air surges to winterize the central and eastern U.S

Pattern Overview and Guidance/Predictability Assessment:

Guidance still depicts an amplified West Coast/Alaska ridge and
e-central U.S. trough upper pattern over medium range time scales
that tends to have above average predictability for the large
scale flow. However there are lower-confidence embedded details
that will be important for resolving sensible weather effects.
This favors a composite guidance blend that is now more reasonable
as the models and ensembles are finally converging upon a more
common solution with respect to potentially deep storm development
off the Northeast U.S. by Day3/Fri and the Canadian Maritimes into
the weekend. The GFS/UKMET are now more in line with recent runs
of the ECMWF/CMC. The stormy solution has been best supported by
GEFS and especially ECMWF ensembles along with WPC continuity over
the past number of days.

By early next week, recent GFS/ECMWF runs and their ensembles
means further open the possibility for greater amplification/depth
of the next shortwaves set to dig into the long-term mean trough
over the east-central U.S. This seems to support coastal low
developments off the Eastern Seaboard.
WPC progs show modest low
developments given uncertainty that are albeit close enough
offshore to effect coastal areas and maritime interests given how
far west/inland the main upper trough axis is dug.


Weather Highlights/Threats:

To the west of the Rockies expect mainly warm and dry conditions.
One exception may be with some modest Pacific
moisture/precipitation that may work into the West Coast mean
upper ridge position into Pacific Northwest terrain.

The downstream pattern under a mean upper trough position laden
with embedded shortwave impulses favors periodic reinforcement of
colder than normal temperatures from the Rockies and Central U.S.
to the East as post-frontal surface high pressure centers track
south/southeast from Canada. A lead cold air mass will cross the
central/eastern states into Fri-Sat with fairly broad coverage of
highs 10-20F below normal and perhaps localized colder pockets
that could produce a few record values. Then by Sun-Tue the next
cold surge with highs 10-25F below normal will again envelop the
central and eastern U.S. and produce some more local record values.

Strong high pressure and sufficiently cold air behind the lead
front may bring potential for some wintry precipitation into
portions of the northeastern U.S. where amounts will be focused by
coastal/offshore low development by Fri. WPC Winter Weather
Outlook graphics depict the upward trending probabilistic aspect
of the forecast.
Elsewhere, clipper systems and trailing cold
cyclonic flow will bring periods of precipitation (mostly snow) to
the Great Lakes/Northeast with activity prolonged by lake effect.
Locations along the eastern slopes of the northern-central Rockies
may see a period of snow as a front digs southward.

Schichtel/Rausch

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Wed Nov 06 2019

Valid 12Z Sat Nov 09 2019 - 12Z Wed Nov 13 2019

  • Central/Eastern U.S Winterization includes Northern Tier to Northeast Snows

Pattern Overview and Guidance/Predictability Assessment:

The larger scale flow pattern is expected to remain amplified this
weekend into next midweek and feature aloft a U.S. West Coast to
Alaska ridge and downstream trough over the central/eastern CONUS.
Overall, forecast confidence in the large scale pattern is above
average, and a favored blend of the latest GFS/ECMWF, GEFS/ECMWF
ensemble means and NBM provides a good starting point for the Day
3-7 product suite.

Weather Highlights/Threats:

To the west of the Rockies expect mainly warm and dry conditions.
One exception may be with some modest Pacific
moisture/precipitation that may work into the West Coast mean
upper ridge position, especially into favored terrain of the
Pacific Northwest.

The downstream pattern under a mean upper trough laden with
embedded shortwave impulses favors periodic reinforcement of
colder than normal temperatures from the Rockies and Central U.S.
to the East as post-frontal surface high pressure centers track
south/southeast from Canada. A lead air mass will cross the
central/eastern states by Sat with a fairly broad coverage of
temperatures 10-20F below normal that could produce a few record
cold values. Then by Sun-Wed an even colder surge with highs
15-25F below normal is expected to spread across the central and
eastern U.S. that may produce more widespread record cold
temperatures.

A lead weekend clipper system and trailing cold cyclonic flow will
bring mostly snow to the Great Lakes/Northeast with snows
prolonged into next week by lake effect. Meanwhile, locations
along the eastern slopes of the northern-central Rockies will see
periods of enhanced snows as the trailing Arctic front digs
southward. The longwave upper flow pattern then suggests potential
for coastal low development offshore the East Coast early-mid next
week, although there is considerable uncertainty in its coastal
proximity and extent of potential wintery impacts. Guidance trends
show increased support for another threat of some heavy snow for
the Northeast and vicinity.

Schichtel
 

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
200 AM EST Thu Nov 07 2019

Valid 12Z Sun Nov 10 2019 - 12Z Thu Nov 14 2019

  • Rockies to East Arctic Outbreak Includes a Heavy Snow/Ice Threat

Pattern Overview and Guidance/Predictability Assessment:
The larger scale flow pattern is expected to reamplify next week
with a U.S. West Coast to Alaska ridge and downstream trough over
the central/eastern CONUS.
The latest GFS/ECMWF and GEFS/ECMWF
ensemble mean solutions now cluster fairly well for much of the
medium range period, bolstering larger scale flow evolution
confidence.

Weather Highlights/Threats:
Arctic-sourced high pressure and lead cold front will surge south
from Canada to produce much colder than normal temperatures over
the eastern 3/4 of the lower 48 states this weekend into next
week.
The surface high pressure center will tracks from the
Canadian Prairies southeastward to the eastern U.S. next week.
Expect a broad coverage of maximum temperatures 15-25F below
normal and a risk of widespread record cold temperatures will
spread across the central and eastern U.S.

A lead weekend clipper system and trailing cold cyclonic flow will
bring mostly snow to the Great Lakes/Northeast with snows
prolonged into next week by lake effect. Meanwhile, locations
along the eastern slopes of the northern-central Rockies will see
periods of enhanced snows as the trailing Arctic front digs
southward resulting in upslope flow. Organized waves of low
pressure along the front are expected to track along a profound
baroclinic zone from the southern Plains to off the East Coast
Mon-Wed. These will produce a swath of moderate rainfall
along/south of the boundary from across the South and
Southeast/Mid-Atlantic, but also a threat of snow/ice north of the
front in the cold air from the s-central Plains northeastward from
the Mid-South to the OH
Valley/Appalachians/Mid-Atlantic/Northeast.
Snows may be
additionally enhanced over the Northeast by coastal storm
development, although there remains uncertainty with coastal
proximity and full extent of wintry onshore impacts. This risk is
depicted in the WPC Winter Weather Outlook probabilities.

There is guidance variance with respect to the handling of
upstream trough energy/heights falls to work through western
Canada and the Northwest U.S. Tue-Thu through an ambient mean
upper ridge. A composite suggests the systems offer modest
precipitation potential focusing over favored terrain of the
Northwest to snowy Rockies.

Schichtel

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
158 AM EST Fri Nov 08 2019

Valid 12Z Mon Nov 11 2019 - 12Z Fri Nov 15 2019

  • Record cold next week with an inland Northeast heavy snow threat

Pattern Overview and Guidance/Predictability Assessment:

Upper ridging over western Canada and also near the Azores will
favor broad troughing over the eastern 2/3rds of the CONUS next
week
. Concurrently, a lost upper low near Baja California will
slowly push across northern Mexico to eventually rejoin the
southern edge of the westerlies late next week. The
models/ensembles were in good agreement on the larger/synoptic
scale but differed in timing/track/strength of the embedded
systems. Overall the 12Z ECMWF and the 18Z GFS clustered fairly
well with their ensemble means and each other to form a starting
point for the forecast. System of interest on Tuesday near Long
Island/Block Island will lift into Nova Scotia/New Brunswick with
modest to perhaps locally heavy snow for interior/northern New
England.


Weather Highlights/Threats:

Cold Canadian high pressure will spill out of eastern Montana
Monday morning through the Central Plains and into the Ohio Valley
by Wednesday, bringing in well below average temperatures that
will likely break daily records across a sizable area of the
eastern half of the CONUS Mon-Wed
. Conversely, some record highs
are possible on Monday over northern California under the upper
axis. Front in the east will carry low pressure just off New
England with a swath of snow to the northwest of the track and
lake-effect snows for the Great Lakes with very cold temperatures
aloft over still warm water. Temperatures will moderate for later
in the week as the high moves offshore and weakens, but highs will
remain about 10-15 degrees below average along and east of the
Mississippi into next Friday
. West of the Rockies, temperatures
will stay above average by about 5-10 degrees. Precipitation could
expand across the Gulf Coast late next week as the upper low once
over western Mexico moves eastward along the I-10 corridor
coincident with a weaker front to its north.

Fracasso

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
140 AM EST Sat Nov 09 2019

Valid 12Z Tue Nov 12 2019 - 12Z Sat Nov 16 2019

  • Record cold next week for much of the central/eastern states

Pattern Overview and Guidance/Predictability Assessment:

Punctuated upper ridging will meander off the coast of California,
favoring troughing east of the Rockies. Over Mexico, a slow-moving
closed low will eventually rejoin the southern edge of the
westerlies after Wednesday and track across the northern Gulf of
Mexico. The models/ensembles were in good agreement overall but
with varying degrees of speed/track/evolution differences in a
fairly perturbed pattern.
The 12Z GFS/ECMWF and 00Z ECMWF formed
much of the base for the forecast with the 12Z NAEFS/ECMWF
ensemble mean as a needed smoother. Largest differences were in
the Southeast as the Mexican upper low and a northern stream
shortwave merge/phase/interact which may induce cyclogenesis and
increase precipitation over the region. 12Z ECMWF appeared too
aggressive but the 12Z GFS too quick (both their biases).
12Z
ECMWF ensemble mean and NAEFS mean were weaker but perhaps better
placed, along with the 00Z/08 ECMWF (just offshore). Secondarily,
troughing in the eastern Pacific may approach California in some
fashion as a shortwave may crest the upper ridge along 140W.
Ensembles have trended more bullish but will need to wait to see
if any precipitation can be realized south of NorCal.


Weather Highlights/Threats:

Cold Canadian high pressure will move out of the central/southern
Plains Tuesday and into the Ohio Valley by Wednesday, bringing in
well below average temperatures that will likely break daily
records across a sizable area of the eastern half of the CONUS
Tue-Wed.
This equates to high temperatures in the 40s from Texas
into the lower MS Valley, 30s in the TN Valley, 20s in the
Midwest, and teens in the northern Great Lakes,
which is more
typical of mid-winter in some locations
. For some, this could be
the earliest in the season such cold will be observed in the
period of record. Temperatures will moderate for later in the week
as the high moves offshore and weakens, but highs will remain
about 10-15 degrees below average along and east of the
Mississippi into next Friday
. West of the Rockies (but including
parts of the Front Range), temperatures will stay above average by
about 5-10 degrees.

Low pressure will move out of New England Tuesday with a swath of
snow to the northwest of the track and lake-effect snows for the
Great Lakes with very cold temperatures aloft over still warm
water. By the end of the week, the upper low once over Mexico will
reach the Gulf and its interaction with a frontal boundary could
spread increasingly heavier precipitation over the Southeast as
low pressure develops near Florida. This may lift northeastward
into next Saturday along the coast with some high elevation snow
possible for the southern Appalachians per the current evolution
in the lingering cold air mass.


Fracasso

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
144 AM EST Mon Nov 11 2019

Valid 12Z Thu Nov 14 2019 - 12Z Mon Nov 18 2019

Pattern Overview and Guidance/Predictability Assessment:

Amplified pattern with rebuilding western ridging and eastern
troughing is forecast to hold into next week. Multi-day
consistency and inter-ensemble system clustering has been subpar
which again leads to a majority ensemble mean weighting next week
.
Trend has been for a bit more interaction in the Southeast between
a exiting/weakening upper low over Mexico and northern stream
troughing through the TN Valley Friday, leading to surface low
pressure organizing around Florida.
How far this moves offshore vs
up the coast remains unclear but have trended a bit closer to the
coast yet still offshore Sat-Sun (enough to keep QPF over the I-95
corridor). In the West, differences between the ensembles were
reflected in the 12Z GFS vs ECMWF/Canadian-- the latter showed an
upper low perhaps splitting off well southwest of California and
remaining offshore as upper ridging builds atop the low rather
while the former moved it inland into the Baja. Ensembles were
split but slightly favored the ECMWF-led solution. Tempered this
via the 12Z/10 ECMWF ensemble mean. This also worked well in the
East/Southeast as the 12Z ECMWF was quite robust with offshore low
pressure vs its ensemble mean. Low confidence in this series of
events in the East.


Weather Highlights/Threats:

Well below average temperatures will ease after Thursday. However,
highs will remain about 5-15 degrees below average along and east
of the Mississippi through next weekend. Along/west of the Rockies
(but including parts of the Front Range and central Plains),
temperatures will stay above average by about 5-15 degrees.

Interaction between the southern upper low and frontal boundary in
the Gulf could spread rain (possibly modest amounts) along the
I-10 corridor and across the Florida peninsula early in the
period. The surface low off the Southeast coast should keep the
heaviest rains offshore, though depending on coastal proximity,
heavy rains may clip the coastline.
Next system into the Pacific
Northwest will provide focused rain/snow to coastal/mountain OR/WA
Thu-Fri with much less east of the Divide. Yet another system may
approach Washington late next Sunday into Monday.

Fracasso

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
146 AM EST Wed Nov 13 2019

Valid 12Z Sat Nov 16 2019 - 12Z Wed Nov 20 2019

Pattern Overview and Guidance/Predictability Assessment:

Upper pattern will transition toward western troughing and eastern
quasi-zonal flow in about a week, after a two successive systems
lift northeastward along the East Coast. In the West, upper
ridging will weaken as it slides eastward atop a closed upper low
moving away from Baja California. This will pave the way for a
Pacific shortwave to dig through interior California as downstream
heights rise in response.

Off the Southeast coast, the models have come into better
agreement with mostly some timing differences as it looms
offshore. Model blend sufficed given recent shifts in the
ECMWF/GFS. 12Z UKMET/Canadian were close enough to the ensemble
range as well. Upstream system will act to kick the lead shortwave
along, but reinforce the surface boundary along the Gulf Stream.
This may develop another low and off the NC coast which should
move quicker out to sea as heights rebound.
In the West, lead
front into Washington will weaken in favor of a stronger shortwave
on its heels. The ECMWF has been most aggressive with this feature
and dug it farther southwest than the other guidance. GFS has been
more in line with the ensembles but given how much upstream
ridging is forecast to build into the Gulf of Alaska, the ECMWF
solution cannot be ruled out completely. This would carry a cold
front through the Great Basin into the Four Corners region by next
Wednesday.

Weather Highlights/Threats:

Below average temperatures in the East will slowly moderate back
toward more typical mid-November values by early next week. Much
of the West will have temperatures above normal by 5-15 degrees
through this weekend, cooling early next week with the arrival of
the next upper trough.

The system off the Southeast/mid-Atlantic coast should keep the
heaviest rains offshore but should be close enough to produce at
least showers along the I-95 corridor. Heavier rain is possible
right along the coast of North Carolina. The strong pressure
gradient between the low sfc high over New England will lead to
windy conditions along the coast. The precipitation shield will
move northward into New England early next week where temperatures
may be cold enough for some snow in higher elevations.

Several systems out of the Pacific will maintain a rather wet
period for at least coastal Washington/Oregon and the Cascades,
with less rain/snow along and just west of the Continental Divide.
With increased troughing toward the Southwest next week, some
light precipitation will be possible late Tue into Wed.

Fracasso

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
144 AM EST Thu Nov 14 2019

Valid 12Z Sun Nov 17 2019 - 12Z Thu Nov 21 2019

Pattern Overview and Guidance/Predictability Assessment:

Upper pattern will transition toward western troughing and eastern
quasi-zonal flow in about a week after two successive systems lift
northeastward along the East Coast.
In the West, upper ridging
will weaken on Monday as it slides eastward atop a closed upper
low moving westward away from Baja California. This will pave the
way for a Pacific shortwave to dig through interior California as
downstream heights rise in response toward the Ohio Valley.

Off the Southeast coast, the models have come into better
agreement with a lead surface low offshore Sun-Mon.
Kicker trough
through the lower MS Valley showed more spread among the guidance
with the UKMET/Canadian quicker than the GFS/ECMWF and most of the
ensembles. Preferred the GFS/ECMWF-led consensus which was closer
to continuity. That kicker trough will likely spin up another sfc
low off the coast that will lift northeastward and possibly
develop in earnest off or near New England, depending on northern
stream flow across the Great Lakes. GFS runs were deeper and
closer to the coast than the ECMWF and the ensemble means. Given
inconsistency in shortwave timing the past several days, preferred
to keep the system outside the 40/70 benchmark next Wed.

In the West, the leading front into Washington on Sunday will
weaken in favor of a stronger shortwave on its heels. The ECMWF
continued to be more aggressive than the GFS and has wobbled
farther south or north with each run. Trend does seem to give
merit toward a stronger shortwave or possibly closed low.  To the
south, the closed low off Baja California may eventually get
tugged back to the coast given enough digging of the incoming
trough Tue/Wed through the West. This would act to lower heights
over the Southwest via interaction/merging of the two features.
Confidence is low in details due to timing uncertainties.

Overall, a GFS/ECMWF/GEFS/ECMWF ensemble mean blend sufficed
through much of the period. Trended increasingly toward the
ensemble means due to their more modest depictions of the western
troughing and exiting eastern system next week.

Weather Highlights/Threats:

Below average temperatures in the East on Sunday will slowly
moderate back toward more typical mid-November values by Tuesday.

Much of the West will have temperatures above normal by 5-15
degrees Sun-Tue before troughing brings in cooler temperatures
within about 5 degrees of average.

The lead system off the Mid-Atlantic coast should keep the
heaviest rains offshore but could be close enough to produce some
showers right along the coast. The strong pressure gradient
between the low and the sfc high exiting New England will lead to
windy conditions along the coast and especially over the nearshore
waters. Please see the Ocean Prediction Center's products for more
information. Second area of low pressure may bring rainfall
farther west, depending on the track. Per the forecast, the
precipitation shield will move northward into New England late Tue
into Wed where temperatures may be cold enough for some snow in
higher elevations Wed-Thu.

Several systems out of the Pacific will maintain a rather wet
period for at least coastal Washington/Oregon and the Cascades
Sun-Wed. Lighter rain/snow along is forecast for areas along the
Continental Divide and even lighter amounts into the High Plains.
With increased troughing toward the Southwest next week,
precipitation chances will increase Wed into Thu. Some rain is
possible for the lower/coastal elevations of southern California
into some of the deserts with higher amounts in the terrain.

Fracasso

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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
136 AM EST Fri Nov 15 2019

Valid 12Z Mon Nov 18 2019 - 12Z Fri Nov 22 2019

Pattern Overview and Guidance/Predictability Assessment:

During the medium range, relatively amplified and progressive flow
from the North Pacific into Canada and the CONUS northern tier
will be flanked to the south by a somewhat less progressive
southern stream with a tendency for upper-level energy to close
off and move a bit more slowly. The ECMWF and GFS showed slightly
above average agreement through the medium range, although both
have shown some degree of variability over the past several runs,
so any consensus is at least somewhat tenuous. Two low pressure
systems are forecast to track northward off the Eastern Seaboard,
the first on Mon and the second Tue-Wed. ECMWF and GFS solutions
showed some timing and intensity differences for these systems,
but the solutions were close enough to be used in a blend. Farther
west, shortwave energy diving south along the West Coast Mon
night/Tue is forecast by the ECMWF/GFS and numerous ensemble
members to close off across the Southwest by late Wed, perhaps at
least partially interacting with upper-level energy associated
with what is now Tropical Depression Twenty-E over the eastern
Pacific. Model/ensemble solutions show general consensus that this
closed upper low should rather slowly move east across the Four
Corners region and southern Rockies by Fri, perhaps reaching the
Southern/Central Plains. At the same time, northern stream
shortwave energy is expected to amplify across the Great Lakes,
pushing a cold front across much of the central U.S.

The WPC surface progs were based on a blend of the 12Z ECMWF/18Z
GFS as well as the 18Z GEFS mean, along with a substantial
weighting of forecast continuity through day 6 (availability of
ensemble and some deterministic model data was limited due to
network issues during model ingest times).


Weather Highlights/Threats:

Initially chilly temperatures across the eastern third of the
nation on Mon
, should moderate toward normal by the middle of next
week. On the other hand areas from the West into parts of the
northern-central Plains will see well above normal temperatures
(up to plus 10-20F anomalies), especially Mon-Tue.

The lead system off the Mid-Atlantic coast should keep the
heaviest rains offshore but could be close enough to produce some
rain along the coast. If any moisture extends farther inland it is
most likely to be over the Northeast. In that case the western
periphery of the moisture shield could contain some snow. The
strong pressure gradient between the low and the surface high
exiting New England will lead to windy conditions along the coast
and especially over the nearshore waters.  Please see the Ocean
Prediction Center's products for more information. Precipitation
coverage and intensity with the second area of low pressure
evolving Tue-Thu are more uncertain, with the Northeast again the
most likely area to see some rain and inland/higher elevation snow
if the moisture shield extends far enough westward.

Favored terrain in the Pacific Northwest/northern Rockies will an
episode of light-moderate precipitation Mon-Tue. The upper low
settling over or near southern California mid-late week would
increase the potential for significant precipitation (mostly rain)
over the Southwest and in particular central Arizona, especially
if additional tropical moisture associated with the eventual
remnants of Twenty-E is drawn northward. Remaining western energy
aloft progressing across the northern half of the lower 48 may
bring a front and accompanying precipitation into the east-central
U.S. by next Thu. A potential wave of low pressure along the
trailing end of the frontal boundary across the Southern/Central
Plains may bring an increase in precipitation to areas from the
Plains to the lower/mid-Mississippi Valley as well. Depending on
the intensity of the low pressure wave, sufficient moisture
advection into the cold air north of the surface front will be
possible to produce some winter weather potential from the
mid/upper-Mississippi Valley to the Great Lakes.

Ryan/Rausch

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