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NorthGeorgiaWX

Monday, October 21

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Good Monday morning!

Transition day today as  our next system comes sliding in later this afternoon and tonight. First, let's take a look at the big picture this morning.

Those purple box lines in and around the rain are Tornado Watches and the red boxes are Severe Thunderstorm Warnings, so ongoing active weather this morning. 

Snap346062886.thumb.jpg.c560bc2b5807d7859ad4a356c48440df.jpg

 

Here's the SPC Day 1 and 2 (Mon/Tue) Severe Weather Outlook for the southeast. 

1807138995_fema04_swody1(1).png.a1b2ddd1fb92b7086456d058058cabdd.png1157766262_fema04_swody2(1).png.f5e02f04fee9c2c754c049deaf8fe4f8.png


These are the thoughts from the Atlanta NWS about today's weather.

Quote

Patchy dense fog across the area overnight should clear by late
morning leaving a mostly dry first half of the day across the area
ahead of the next system forecast to impact the area. While the
local forecast area sits in southwesterly flow, an upper level
longwave trough to our west and associated cold front will push
towards the area through the day today
. As moisture from the Gulf
overspreads the area, chances for rain begin to increase in the
early afternoon in northwestern portions of the area
. Chances for
showers and thunderstorms will continue to increase across the rest
of the area into the evening and overnight periods.
While
instability overall is somewhat limited across the area, there's
still the potential for some strong to isolated severe storms across
the area and the storm prediction center has much of the area
outlooked in a Marginal Risk for severe storms
. PWATs also will be
increasing ahead of the front in the 2+ inch range
across the area
so some periods of heavy rain may be possible. Overall, rainfall
totals aren't too impressive across the area with the frontal
passage, around a half an inch to an inch and a half with the
highest totals across northwestern Georgia
. As such, portions of
northwestern Georgia are outlooked in a Marginal Risk for excessive
rainfall.
The front will be clearing the area during the day on
Tuesday and once the front and associated precipitation clears
completely by late Tuesday afternoon, we will be left with some
slightly elevated winds during the day on Tuesday in addition to
much cooler temperatures and drier air filtering in.

 

 

The SPC only talks briefly about our side of town as most of the severe weather is well to our west today.

Quote

Later in the day and through the evening, southerly surface winds
will bring low to mid 70s F dewpoints northward across southern AL
and the FL Panhandle. This may support a few strong storms as the
front continues east, beneath 50 to 60 kt mid to upper flow.

 

So while there may be some severe thunderstorms around, they will be very isolated and no tornadoes are expected. Wind will be the biggest threat.
Day 1 Tornado Outlook

day1probotlk_1200_torn.gif.1d48ed26cdf268c1320e52aaa6f7bad4.gif

 

Day 1 Wind Outlook

day1probotlk_1200_wind.gif.33667ff4975712115a465d1cead484be.gif

 

After the front pushes through tomorrow, nice fall like temperatures return for a day or two and then we head back to the unsettled weather that I was mentioning yesterday. 

Quote

The long term portion begins with high pressure working into the
southeast states including the local area with a cold NW drainage
flow. This will allow for temps to fall into the upper 30s for the
NE mountains and lower 40s elsewhere across North GA. There will
be 5 to 7 degrees of dewpoint depression but could still see some
patchy frost given light winds.

The high will remain the dominant feature through Thu afternoon
although airmass will modify slightly from upper 60s on Wed to
around 70 for Thu afternoon.

 

It's after Thursday when our weather will take a turn toward a more active weather pattern for Friday and into the weekend.
 

Quote

After this, it will be a squeeze play for the local area as
northern stream upper level energy slides into the central plains
while gulf energy moves in from the SW
. This will allow for a
combination of upper energy forcing and isentropic forcing to
produce likely pops. Should these trends continue with subsequent
forecasts, these pops will need to be increased to categorical.
Looks like the higher pops will stick around for awhile with no
quick frontal progression.
Significant clearing not anticipated
until the very end of the extended period when high bridges over
the area for Sunday.

 

The Weather Prediction Center was discussing the potential for "southern stream separation" yesterday and again in their Extended Forecast Discussion today.

Quote

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.

The separation they refer to is the possibility of an upper low separating itself from the northern stream flow and slowly meandering across the southern part of the US on a NE track that takes it just to our west. That possibility raises concerns for heavy rainfall for us in Georgia as it leaves us on the wetter side of the storm. 

In the Model Diagnostic Discussion, the WPC says this.

Quote

07Z update: The operational ECMWF continues to be stronger with
the shortwave and digging trough across the southwest into
southern Plains toward the end of the forecast period. However,
the operational CMC and UKMET have also trended that way, leaving
the GFS as the weaker/flatter solution. With that in mind and
given the trend toward a more separated southern stream solution,
the preference is for a ECMWF/ECENS solution with some inclusion
of the UKMET/CMC
. Lesser weight given to the 00Z GFS, especially
by Day 3. Forecast confidence drops to below average by day 3
given the uncertainty and model spread.

 

At the moment it appears that the southeast has the potential for a heavy rain event this weekend and the Atlanta NWS is starting to think the same thing.

Quote

After this, it will be a squeeze play for the local area as
northern stream upper level energy slides into the central plains
while gulf energy moves in from the SW. This will allow for a
combination of upper energy forcing and isentropic forcing to
produce likely pops. Should these trends continue with subsequent
forecasts, these pops will need to be increased to categorical.
Looks like the higher pops will stick around for awhile with no
quick frontal progression.
Significant clearing not anticipated
until the very end of the extended period when high bridges over
the area for Sunday.

 

The track will determine where the most rain will fall, and as you have seen, it tends to change as the time gets closer, but here is the latest 7 day rainfall forecast from the Weather Prediction Center. Keep in mind, this will be an evolving system for the next 3-4 days, so will be watching the trends.

wpc-se-total_precip_inch-2264000.thumb.png.94e434edb4dc4619d2d30d4c225585a4.png

 

That's it for now. In the time it took me to type all of this,  a new Severe Thunderstorm Watch has been issued.

Snap346062889.thumb.jpg.2407ffe0fccaa35107afb6ef073f0277.jpg

 

The weather will be very active today and I'll have updates for our area as necessary. Again, not expecting any big severe weather event for us, maybe an isolated severe thunderstorm and no tornadoes. 

Have a great Monday! 🙂

Winter begins in 62 days...

October's face, benign and mellow,
Turns nuts to brown and leaves to yellow;
But (like the Scorpion, sting in tail)
He ends with frost and scourging hail.

–Jan Struther (1901–53)

forecast-21.jpg.9b69024168c3b9faa116028cbd122444.jpg

 

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I didn't see much of anything for here in south east georgia .  Did I miss something?  I looked at the short range and long range models.  When it gets to AL/GA line it fizzled out  Even in NW Ga it was just a very thin line?

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5 minutes ago, RickyD said:

I didn't see much of anything for here in south east georgia .  Did I miss something?  I looked at the short range and long range models.  When it gets to AL/GA line it fizzled out  Even in NW Ga it was just a very thin line?

The clouds may negate any severe parameter issues. The problem is in the timing to the parameters, some are strong when others are weak, and that also helps to remove some of the severe potential. There may be none at all, or some could see a few severe storms, we'll need to wait and see how the day progresses.

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The heavy rainfall at the end of the week, does it seem like it will have severe weather with it, or just the rain, or is it too early to tell?

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58 minutes ago, Asperman1 said:

The heavy rainfall at the end of the week, does it seem like it will have severe weather with it, or just the rain, or is it too early to tell?

That one is too early to know. Forecast confidence is low for that period at the moment.

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WPC

Quote

Height falls should then act to carve out an amplified central U.S. upper trough later
week. Pattern evolution uncertainty grows quickly thereafter,
resulting in low forecast confidence for the southern and eastern
U.S
.  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 represented by 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 represented by recent GFS runs.

Overall, the most recent operation models that indicate scenario 1
show a trend toward a slower eastward ejection
of the amplified upper trough
.  On the other hand, the UKMET is
hinting at a tropical low center lingering off the Texas coast as
the upper trough approaches.  The GEFS/EC/CMC ensembles are mixed,
with ECMWF ensemble members showing scenario 1 but with highly
variable forward motion of the associated upper-level shortwave.
With the consideration of the amplitude of the upstream upper
ridge, the next main upper trough should 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.  WPC progs modestly lean the forecast
to show such potential.
 However, with the ensemble means continue
to support a less prominent system due to the high degree of
uncertainty, the new WPC prognostic charts now show a less
prominent frontal wave moving across the Southeast during the
weekend compared with previous progs.

 

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Hmmm, conflicting thoughts?

Quote

Stronger shortwave dropping through Rockies into the southern
Plains early to mid week

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preference: non NCEP blend (ECWMF,ECMWF mean, UKMET, CMC)
Confidence: Slightly below average

Models are in pretty good agreement though 12z Wed (23rd) with the
shortwave energy dropping southward through the Canadian Rockies
and into the northern Plains. Thereafter spread increases
significantly. The non NCEP guidance (ECMWF/UKMET/CMC/EC MEAN) all
show a stronger wave and a trough digging deeper to the southwest
across the Rockies and Plains...eventually resulting in the
development of a cutoff low.
The 12z GFS and NAM show a weaker and
more progressive system.

The last several runs of the ECMWF have been very consistent with
the deeper and slower trough...and with the other non NCEP models
trending in this direction as well...it would appear this
slower/deeper solution is becoming increasingly likely. Thus WPC
will continue to prefer a non NCEP model blend for this system
after 12z Wed
. Confidence has increased some, but is still
slightly below average given the spread...however if the new 12z
non NCEP models remain consistent with their deeper/slower
solutions, then confidence would increase towards average for this
system.

 

 

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These are the winds at the 300 mb level, and over that rainfall to our west, that height is about 31,400 feet. Nice jet ripping around the right front exit region of the trough. The leading edge is about 84 mph and 104 on the backside. But the winds back over Arkansas are roaring at 160 mph.

Snap346062897.thumb.jpg.38fb2d62b7f2964986740b0945804171.jpg

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