Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 221948
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
248 PM EST Sun Jan 22 2017

.SYNOPSIS...
Numerous waves of energy will bring rounds of heavy rain and
thunderstorms to the area tonight. A vigorous low pressure system
will sweep toward the region tonight and move northeast of the
Carolinas on Monday. Mild high pressure will move in Tuesday and
Wednesday until a cold front crosses the region Wednesday night.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 245 PM EST Sunday: Complicated forecast today. Plentiful low-
level moisture has kept quite a bit of cloudiness across the area
and inhibited instability increase. The latest mesoanalysis has some
small amounts of sbCAPE creeping into our southern zones (100-250
J/kg). Not a lot of low-level shear just yet since the surface low
is still to the west, but plenty of deep-layer shear already in
place (50-60kt). So for the synoptic setup, we have the deep upper
closed low over the ArkLaMiss area that will continue to dive
southeast into the Deep South before lifting northeast again toward
the Carolinas. The attendant surface low currently in SE Alabama
will lift northeast toward the Southern Appalachians through the
period. Warm frontal convection ahead and northeast of the surface
low will begin spreading into our area this evening, with a
secondary round of convection possible on its heels associated with
the deep surface low itself. Latest trends have been for a decrease
in the look of the severe weather threat across most of our NC
counties, except the CLT metro area, but very little change across
our Upstate SC and NE GA counties.

So, if the models are to be believed, sbCAPE will increase across
the area over the next few hours, with the max around 03z. This is
not collocated with the best low-level shear and so resulting SigTor
Parameters, on the more bullish NAM, are at best around 4 in extreme
southern zones (closer to 1 on the GFS). This is hardly a reason to
let down one`s guard, but obviously the greater threat is to our
south where a significant severe weather/tornado outbreak is
expected. However, we all know that if the shear is high enough, it
doesn`t even take 500 J/kg sbCAPE to get things going in an HSLC
event. Overall, as temperatures aloft cool over our area, the hail
threat should increase through the evening, as will the damaging
wind and tornado potential. Right now thinking isolated tornadoes at
best but will have to continually reassess the threat through the
afternoon and evening as we see how CAPE trends evolve.

Other issue is the QPF. WPC does have us in a slight risk of
exceeding flash flood guidance, and for the next 24 hours or so
looking at widespread 1" amounts with 2-3" over the mountains. Add
that to what we`ve already had this weekend and it`s possible we
could see some isolated flash flooding. Some areas across the upper
Savannah Valley have seen over 2" in the past 24 hours, but so far
area waterways seem to be handling this precipitation with only
minor rises. For now, do not see the need to issue a Flash Flood
Watch.

Temperatures will remain warm, with once again overnight lows closer
to seasonal average highs. Should see more reasonable temperatures
across the mountains tomorrow, though still not quite seasonal,
with the Piedmont in the upper 50s to lower 60s.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
As of 100 PM EST Sunday: Fairly robust cyclonic flow will remain
atop the region Monday night in the wake of departing closed upper
low. Additional pcpn chances will increasingly be limited to NW NC
as the night wears on given that showers should become forced solely
by upslope/CAA along with the depth of moisture becoming
progressively shallow. Model llvl wind progs 45-50 kts at 85H
leading to the ongoing probability of strong high elevation wind
gusts into Tuesday morning. The snow shower threat should be highly
elevation dependent as it looks to be a race between lowering
freezing levels and lessening moisture.  At this point, feel that
high elevation snowfall of an inch or two is not out of the question
throughout the Tenn border counties.

Expect the upper flow to deamplify on Tuesday and sfc pressure
gradient to loosen considerably. Model crosssections are progging
dry conditions throughout the depth of atmosphere, so expect
sunshine with max temperatures 8-10 deg f above climo.  Lower level
return flow/lee troughing looks to develop on Wednesday with a
questionable amount of moisture return ahead of encroaching yet
weakly forced cold front. Sunshine should progressively fade behind
increasing clouds that day, but there should be a downslope aided
boost to max temperatures, maybe even category or two warmer than
Tuesday`s readings.  Any small later day shower chances still should
be limited to the mountains.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 200 PM Sunday: The recently posted op 12z EC is consistent
with it/s earlier run in effectively and quickly brushing baroclinic
zone to the coast during Thursday.  This will keep the sensible wx
fcst unchanged from previous thinking featuring token shower
chances, especially Wed nite into Thu am. Also, the onset of a
cooler period of weather is on tap to start off the period with a
shift to below normal max temperatures for Friday, the first
occurrence since 10 January.  Coincident with the chillier airmass
overspreading the region, a period of NW flow snow showers remains
possible Thu nite into Friday. The large scale pattern for next
weekend will feature an eastern conus l/wv trough and below normal
temperatures.  At this point, pcpn chances will be limited to just
periodic nw flow snow showers.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: Complicated forecast for this TAF period with
widespread MVFR to IFR cigs/vsbys this afternoon. Could see
intermittent improvement to VFR/MVFR before the first round of
SHRA/TSRA moves in. Timing is still uncertain but should see
increase in SHRA toward 00z, with rounds of TSRA off and on through
about 06z. Cigs should remain low for most of that period, but
behind the TSRA, guidance is indicating some improvement in cigs
before the surface low approaches after 06z. Have not depicted this
improvement in the TAFs due to low confidence plus lack of extra
lines. May see some improvement again toward the end of the period
but line restrictions strike again, so only hinted at this. Winds
should be SE to begin, possibly VRB and gusty in TSRA, veering to S
and SW and occasionally gusty. Winds should continue to veer toward
W by the end of the period but will refine those details with later
issuances.

Outlook: The very unsettled pattern will continue through Monday as
the upper low pressure system moves slowly east of the area. This
may allow periods of rain and/or restrictions to continue. Expect
gradual improvement by Tuesday but with moisture returning ahead of
the next cold front Wednesday into Thursday.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High  80%     Med   64%     Med   66%     High  93%
KGSP       High  85%     High  81%     High  85%     Med   77%
KAVL       High  86%     Med   78%     Med   69%     High  88%
KHKY       High  85%     High  86%     Med   77%     High  94%
KGMU       Med   77%     Med   76%     Med   64%     High  84%
KAND       Med   74%     Med   79%     Med   63%     High  88%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...CSH
NEAR TERM...TDP
SHORT TERM...CSH
LONG TERM...CSH
AVIATION...TDP



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