Severe Thunderstorm Warning 34, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
251 PM EDT Fri Apr 25 2025

.SYNOPSIS...
A stationary front across our area provides a focus for scattered
showers and thunderstorms this evening and again Saturday afternoon
and evening. Dry high pressure moves in for Sunday and Monday. Daily
chances of showers and storms return Tuesday through late next week,
along with above-normal temperatures.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 157 PM Friday: Afternoon water vapor satellite imagery depicts
a weak upper trough over the Lower Mississippi Valley. Guidance is
in excellent agreement that this feature will lift northeast across
the Southern Appalachians this evening into the overnight hours.
Increased forcing within an anomalously moist airmass has allowed
for deep convection to blossom across central Tennessee into Alabama
and eastern Mississippi. A few scattered lead showers and storms are
also noted across far northern Georgia into eastern Tennessee. Much
of the western Carolinas and northeast Georgia remain dry as of this
writing with only a couple scattered showers trekking across the
Smokies. Copious cloud cover has precluded the development of much
instability and thus is expected to help keep things quiet through
the rest of the afternoon into the early evening hours, although a
stray shower cannot be discounted at any given location. As we head
into this evening, the 12z suite of CAMs is in good agreement that
upstream convection will grow upscale into a loosely organized QLCS
that will push into western portions of the area generally around or
after 7-8pm. Convection will weaken with waning instability with a
broken band of showers progressing east of I-26 into the overnight.
An accompanying modest cold pool may prove to be sufficient for a
few embedded strong wind gusts, mainly west of I-26, but an
otherwise unfavorable environment both thermodynamically and
kinematically will limit any severe weather threat.

A few scattered showers may linger east of I-77 Saturday morning,
but should quickly push out of the area shortly after sunrise. A
more potent northern stream trough swinging across the Great Lakes
region will send a surface cold front towards the area during the
day with the boundary sliding into the mountains and towards the
foothills/Piedmont late Saturday afternoon. By this point, the
region will reside behind the trough axis of the original trough
with dry mid-level air arriving within the northwest flow regime.
Flow will also have a downslope component off the mountains, which
will further prove detrimental to the development of pre-frontal
convection. The result has been a continued down tick in PoPs
Saturday with only isolated to widely scattered showers and perhaps
a couple thunderstorms ahead of the front, generally along and south
of I-85. Afternoon highs will recover nicely ahead of the front with
temperatures climbing back into the low 80s.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
As of 100 PM Fri: Sfc cold front looks to have cleared the CWA by
Saturday evening, although the trailing secondary push of cooler
and drier air may still be near the Appalachian spine at that
time, taking until Sunday morning to expand southeast across the
whole CWA.  Remaining PoPs diminish overnight as the upslope layer
dries out along the NC/TN border, and as more stable air reaches
the Piedmont and any lingering convection fizzles. Behind the
secondary front, sfc high centered near Lake Erie will nose into
the CWA thru Sunday, shifting to the Mid-Atlantic coastal plain
by Monday morning in advance of the upper ridge axis. Max temps
return to about normal Sunday but moderate a little above normal
for Monday. Low RH at or below 30% is possible in our northern
NC foothills and the eastern portion of our Piedmont zones on Sun
and Mon.

For the NE half of our CWA, more or less NE of I-26, pretty high
confidence that subsidence will totally inhibit any convection
Sunday and Monday, under profiles dry enough to warrant PoP near
zero during that timeframe. Return flow however will set up on
the periphery of the sfc high, ahead of the ridge, producing a
midlevel moist layer and very weak upglide Sun night into Monday
morning which leads some models to produce spotty QPF. That is not
entirely out of the question although the forcing and lift are so
weak it warrants only a slight-chance PoP, mainly in the Smokies,
Balsams and vicinity.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 130 PM Fri: Sfc high will continue to shift southeastward
Mon night; ridge axis will tilt toward the East Coast as upper
pattern turns more progressive. To wit, cyclogenesis occurs in the
central Plains as a shortwave shears off the Western trough; those
features track across the northern Great Lakes Tuesday and the sfc
high moves fully offshore. South to southwesterly flow from the
surface to 700mb will promote a warming trend over the CWA through
late week and also bring back springlike sfc dewpoints. Temps will
run around 10 above normal Wed and Thu.

The Appalachians look to be on the upstream side of the ridge by
Tuesday, and subsidence inversion weakens to the point deep ridgetop
convection again appears possible.  The front associated with the
Great Lakes low is generally shown to stall to our north Wednesday,
keeping us more or less in the warm sector. Forcing generally looks
weak, aside from diurnal instability. PWATs will rise to near the
90th percentile of climo. The return of sfc moisture does support
at least seasonable diurnal instability of 500-1000 J/kg each day.
Coverage is expected to be better Wednesday compared to Tuesday as
profiles become slightly more favorable for convection. Chances
increase further Thursday as the southern shortwave moves into
the lower MS Valley.

Convection Tue-Wed looks most likely to be garden-variety with
actual thunder likely remaining isolated. Locally heavy rain may
however lead to a localized flash flood threat each day. Deep
shear increases as the shortwave approaches Thu, increasing the
likelihood of at loosely organized multicell convection and a
slightly better chance of severe winds and flash flooding.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: A myriad of restrictions will plague all
terminals through the TAF period. A band of low-level stratus
continues to pivot across portions of the Upstate into the mountains
and foothills with attendant restrictions at KAND, KGMU, KGSP and
KHKY. At least temporary MVFR ceilings will remain an issue for the
next several hours before all sites are expected to return to VFR. A
few showers may develop across the mountains this afternoon where a
PROB30 remains at KAVL. While a stray shower cannot be ruled out
elsewhere, confidence is too low to mention in the TAF. Thereafter,
attention shifts to a line of showers that is expected to push into
the area late this evening into the overnight hours. Embedded heavy
rain may bring temporary reductions in visibility with another batch
of MVFR ceilings behind the band of showers. Conditions are expected
to return to VFR by mid to late morning Saturday.

Outlook: A few isolated to scattered showers and storms will be
possible Saturday afternoon ahead of an advancing cold front, but
coverage will be much less compared to the last few days. Dry high
pressure returns Sunday into early next week.

&&

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

&&

SYNOPSIS...Wimberley
NEAR TERM...TW
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...TW

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