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359
FXUS62 KGSP 111434
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1034 AM EDT Sat May 11 2024

.SYNOPSIS...
Dry high pressure will remain in place through the weekend, with
mild temperatures and clear skies.  An unsettled pattern will take
shape late Monday, with rain and thunder chances return and lasting
through Wednesday.  After a brief stint of dry weather on Thursday,
rain may return late next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 1015 AM: No major changes to the forecast thinking. Mostly
clear skies east of the mountains, but ridgetops are already seeing
some shallow cu develop in upslope NW flow. A sprinkle is not out
of the question in a few spots, but inversion should limit the
depth of these such that PoPs remain well below slight-chance
through mid-afternoon. Updated temps/dewpoints per recent obs;
still think we will see highs a tad below normal.  A weak cold
front still looks to reach the mountains in the late afternoon,
and lapse rates will improve a bit aloft such that deeper convection
and scattered showers should be able to develop near the TN border
from then until after sunset. Guidance still split as to whether
any of these showers will surive downslope into the foothills or
upper Piedmont. Did not yet add any chances in those areas but will
take another look once all 12z cycle runs come in. Winds increase
through the day with gusty winds across the mountains and possible
elsewhere, but with lower magnitudes than on Friday.

Shower chances taper off during the evening with dry conditions and
clearing skies overnight. Winds taper off outside of the mountains
during the evening then across the mountains overnight. Lows will
be around 5 degrees below normal.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 220 AM EDT Saturday: Steady height rises Sunday and Sunday
night as a shortwave ridge translates across the Southeast.
Meanwhile, a compact upper low will break away from the mean
flow and amplify downwind of the Continental Divide.  On Monday,
it`ll make tracks across the Ozarks and a swath of DPVA forcing
will lift off the Gulf Coast into the Carolinas by Monday night.
Moisture flux into the Carolinas on Monday night is uncertain,
given that the GFS and CMC as well as many of their ensembles now
attempt to produce some upstream convection over southern AL/MS
into the FL Panhandle, which could sap the improving WAA regime
of better moisture; consequently, forecast rainfall totals still
exhibit low certainty and a wide range of possibilities.

Whatever the case may be, isentropic ascent will be improving from
Monday afternoon onward, pumping any available moisture into the
region overnight.  Operational guidance depicts a short period of
ENE winds on Monday, which, although they fall short of producing a
CAD wedge, will nonetheless produce a shallow dry layer just above
the surface in advance of the approaching system.  Consequently,
rainfall will likely begin as intermittent light sprinkles, and not
develop into full-on showers until the overnight.  Temperatures on
Sunday will be around normal, falling to a solid category below
normal on Monday as increasing cloud cover limits solar insolation.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 247 AM EDT Saturday: Rain is all but a certainty on Tuesday as
a potent upper low migrates into the lower Ohio Valley and drives
a surface low across TN/KY into the Mid Atlantic.  Whether any
instability will be able to develop remains in question; the vast
majority of LREF ensemble members depict weak in situ CAD in place
Tuesday morning (as a result of saturation of the formerly dry air
mentioned in the short term discussion)...but ensemble soundings
indicate that low-level WAA will be strong enough for this weak
wedge to mix out entirely by afternoon.  So, it`s not clear how
much instability will develop, or whether it`ll be for the entire
area versus just the southern zones...but it`s a real possibility,
and should it occur we`d potentially be under the gun for some
severe weather with a 500mb speed max exiting the lower Mississippi
Valley and driving deep shear through the roof for our area.

Wednesday will be more of a slam dunk for instability,
with only slightly lower dewpoints but significantly warmer
temperatures and no CAD to overcome.  Deep shear will be a little
less pronounced.  So, confidence on thunderstorms is higher for
Wednesday afternoon/evening, but severe risk, while still elevated,
will be a little lower.

Thursday and beyond, the forecast gets more mushy.  A brief
period of upper ridge is expected on Thursday and Thursday night,
before another southern stream disturbance arrives on Friday.
Timing tough to pin down this far out, but a best guess would
put rain arriving Thursday night or very early Friday morning.
Active weather will last into the weekend.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: NW wind with mountain stratocu continues this
morning. Wind speeds pick up and turn W to SW for the afternoon. NNW
and gusty at KAVL. VFR stratocu increases across the mountains with
FEW to possibly SCT elsewhere during the afternoon. Scattered SHRA
develop across the mountains during the afternoon then diminish
early in the evening. Chance too low for a KAVL mention for now.
Winds turn back to NW, stay NNW at KAVL, and diminish during the
evening with clearing skies.

Outlook: VFR conditions continue on Sunday. Moisture returns late
Monday with active weather and associated restrictions Tuesday and
Wednesday.

&&

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

&&

$$

SYNOPSIS...MPR
NEAR TERM...RWH/Wimberley
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...RWH