Area Forecast Discussion
Issued by NWS Greer, SC

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241
FXUS62 KGSP 230558
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1258 AM EST Mon Jan 23 2017

.SYNOPSIS...
A vigorous low pressure system will move east across the
Carolinas today then northeast up the East Coast through mid week.
Mild high pressure will move in Tuesday and Wednesday until a cold
front crosses the region Wednesday night.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
As of 1255 AM EST Monday:  A final round of moderate shra/tsra is
underway as a broken line of convection slides northeast across
the Upstate into Western NC.  Severe parameters are looking ever
weaker as times progresses, therefore think those threats have
all but subsided.  However, continued rainfall across portions of
the Upper French Broad valley has led to minor stream rises, thus
continued monitoring will be needed for possible advisory issuance
over the next few hours before all heavier precip exits the region.
Otherwise, all convection will sweep out of the Upstate into Western
NC with time this morning, likely exiting the region north of I40 by
around or just after daybreak.  Behind the departing precipitation
am expecting patchy fog as the PBL remains very moist, and winds
weaken a bit before veering and increasing out of the NW into
the daylight hours.  As for the fcst, tweaked t/td/pops and sky
to reflect latest obs/sat/radar trends and left the remainder of
the fcst as it was.

Previous Discussion: 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 THIS 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 SUNDAY/...
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 /06Z MONDAY THROUGH FRIDAY/...
At KCLT and Elsewhere:  A mixture of VFR/MVFR and IFR through the
evening/morning at all sites as bands of shra/tsra move through
the region associated with a large upper low pressure system
sliding through north AL/GA at this time.  Multiple round of
convection can be expected at most sites through daybreak, however
the SC sites will likely see the least amount of shra/tsra given
current placement and little if any activity to the west.  Thus,
prevailed shra with vcts at the SC sites with MVFR/VFR cigs/visb,
with all weather removed by around 08z.  As for the NC Sites,
expecting continued convective activity along with vary degrees
of cig/visb restrictions through the night, with all wx removed
around 11z-12z.  Winds will remain backed to the e/ne and gusty
ahead of the tailing line of convection that is currently just west
of I26, with all sites west of said line veered sly and slightly
weaker however still with a few gusts.  Generally, expecting a
period of MVFR after any shra exits the region, before conditions
lower further into the IFR/LIFR range as the very moist PBL settles
leading to patchy fog and low stratus.  Otherwise,  a final round
of deformation zone showers is possible behind the departing upper
low this afternoon therefore all sites feature prob30s for such.
Cigs will finally recover late in the day at all sites, as winds
veer further to the nw and get quiet gusty.

Outlook: Conditions will improve on Tuesday as the atmosphere
dries out, all ahead of another cold front that is expected to
move into the region by late week.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       Med   74%     Med   63%     High  83%     High  95%
KGSP       Med   78%     Med   64%     High  87%     High 100%
KAVL       Med   76%     High  84%     High  81%     High  81%
KHKY       Med   78%     Med   69%     Med   76%     High  83%
KGMU       Med   79%     Med   67%     High  89%     High 100%
KAND       High  90%     High  86%     High  95%     High 100%

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...CDG/JAT/TDP
SHORT TERM...CSH
LONG TERM...CSH
AVIATION...CDG



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