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000
FXUS62 KGSP 160730
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
330 AM EDT Tue Apr 16 2024

.SYNOPSIS...
Very warm and relatively humid weather will continue through
Friday. Small chances of showers and storms exist today and
Wednesday over the mountains, and extend into the Piedmont
Wednesday night.  More widespread showers and thunderstorms are
expected with a front reaching the area Friday, with unsettled but
cooler weather continuing through the weekend as the front slowly
moves through the region.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 241 AM Tuesday: Early morning water vapor imagery depicts a
potent closed upper low ejecting out of the Rockies and into the
Central Plains. Large-scale ascent has initiated scattered clusters
of deep convection across the Plains with high resolution models
bringing this activity east into the Midwest and middle Mississippi
Valley today. Ahead of this upstream activity, a lead shortwave
perturbation was noted over the Tennessee Valley. Subtle forcing for
ascent will overspread the Southern Appalachians early this
afternoon and should prove sufficient to initiate isolated to
scattered convection across the northern mountains where ascent is
expected to be maximized. Some of this activity may drift east out
of the mountains and into the foothills by mid to late afternoon,
but forecast confidence is low as to how much coverage may be
realized outside of the mountains. By the time convection attempts
to move out of the mountains the passing shortwave will be off to
the east with the subsident side of the trough and a tall upper
ridge building into the region.

As was the case yesterday, there will be a conditional threat for a
few strong to marginally severe storms. Surface-based instability
will range from 1500-2500 J/kg with modest mid-level lapse rates and
30-40 kts of deep-layer vertical wind shear. This will allow for
weakly organized multicell clusters capable of locally damaging wind
and small to marginally severe hail. Otherwise, temperatures will be
quite warm today with highs soaring into the low to upper 80s. A few
locations in the lower Piedmont may make a run at the 90 degree
mark. These temperatures will be 10-15 degrees above record with
daily highs being challenged at GSP and Charlotte. Heading into
tonight, broad height falls will gradually overspread the
Appalachians as the upstream trough lifts through the Mississippi
Valley. A band of showers depicted in the CAMs will try to make a
run at the area during the early morning hours but will encounter an
increasingly hostile environment. A residual elevated mixed layer
will advect into the area along with a strengthening subsidence
inversion. This will result in very deep and dry sub-cloud layer
beneath the high level stratus. The column will slowly saturate from
the top down as initial moisture and showers move in, but forecast
soundings indicate that full saturation to the surface likely won`t
be achieved. Thus, most of the light rain will evaporate as virga
but will leave a slight chance for rain in the event a few sprinkles
or light rain is able to survive to the ground across the mountains.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
As of 130 AM Tue: Occluding low pressure crossing the Great Lakes
Wednesday will pull a weak cold front into the CWA late in the day
or possibly Wednesday night. The front will be accompanied by a
broad area of weak DPVA south of the upper low. Vertical profiles
feature some mid to upper level moisture, enough to support a
moderately cloudy forecast, but also a subsidence inversion with
dry low levels.  That would have to be overcome to support deep
convection. Some storms are likely to fire diurnally in KY/TN
along the sfc front, and could make a run into the NC mountains
Wednesday evening; trough axis will pass overnight and might finally
make for viable convective profiles, although model output is not
clear as to whether the front pushes through the CWA or washes out
overnight. PoPs will be confined to chance range at best and mainly
over the northwest half of the CWA. Warm weather will continue,
with maxes 7-10 above normal, although cooler than either Tuesday
or Thursday owing to the cloud cover.

For Thursday, as noted above it is difficult to say whether we
will actually have experienced any airmass change; the GFS and EC
seem to actually settle the synoptic front into the area, whereas
the NAM and GDPS show it stalling to our north. The difference
in the two camps is small in terms of impact. We will be under
a shortwave upper ridge between the departed Great Lakes low and
the next trough passing the Rockies, which will initiate the next
cyclogenesis event in the Plains. Vertical profiles remain dry
in the low levels and trend drier higher aloft under the ridge.
Accordingly, Thursday looks to be a sunny day and likely the
warmest of the period. Record high at GSP could be threatened,
although probably out of reach elsewhere.  Convection appears a
somewhat better possibility in the NAM-like solution. Prog profiles
remain capped over the Piedmont, but in a setup somewhat like what
we saw Tuesday, the NAM shows the cap eroding via mixing over
the mountains and deep convection becomes plausible, although
there is no forcing aside from ridgetop convergence. The drier
dewpoints in the GFS solution show the LCL likely too high to
reach. The NAM solution appears a little more plausible based on
the initial orientation of the front and lack of much forcing when
it reaches the area. If it pans out, CAPE values won`t be as high
as Tuesday, but a highly isolated thunderstorm can`t be ruled out
over the mountains. This chance looks low enough not to introduce
a slight-chance PoP at this time.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 300 AM Tue: By Thursday evening, the ridge axis should have
moved just east of the CWA and all solutions depict the central
CONUS frontal system moving into the Ohio Valley and inititaing a
band of storms, possibly aided by an amplifying frontal wave. Not
yet very confident such activity would reach the CWA before dawn,
but we introduce a small chance PoP for the western mountains
overnight, and feature peak PoPs during the day Friday. Low-level
flow will turn westerly Friday and temps will fall back several
degrees compared to Thursday. The actual synoptic looks to reach
the area until Friday night or Saturday, as broad upper trough
sags over the Midwest and Northeast states. A lull in precip is
likely to occur east of the mountains overnight as a result of
downslope drying.

The front will remain in our vicinity through the weekend and this
suggests unsettled weather and periodic PoPs remain in the forecast
Saturday and Sunday. Model solutions differ as to whether the front
actually stalls and reverses, but divergence invof the base of the
trough, and/or a weak shortwave riding along the front over Texas,
look likely to produce frontal waves that at least slow down its
progress. Cooling trend looks to continue through the weekend,
but of course the frontal position is the big question. Sunday
is the day with lower confidence on temp, with very large spread
among guidance; our forecast is more or less in the middle, and
below-normal for high temps. On another note, modest instability
of at least a few hundred J/kg of CAPE will be present on the
warm side of the front, along with decent 0-6km shear of 30-40
kt. Clusters of storms producing heavy rain and marginally severe
wind gusts and hail might result.

A well defined trough is shown to develop in the central CONUS
Sunday night into Monday, and as that swings east it may initiate
one final round of precip before carrying the front south and east
of the area for good, allowing cooler weather to continue Mon, with
high pressure possibly giving us a break in precip circa Tuesday.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: VFR conditions will prevail at all terminals
through the TAF period. High clouds will continue to stream across
the region from the northwest with few to scattered mid-level
cumulus this afternoon. Winds will be light and at times variable
overnight and then weak out of the north this morning turning to out
of the south by the afternoon. A few isolated showers and
thunderstorms cannot be ruled out at any terminal this afternoon,
but confidence in when/where any storms may develop is too low to
warrant mention in the TAF at this time.

Outlook: Isolated SHRA/TSRA are not out of the question at any
terminal through Wednesday afternoon. Otherwise VFR generally will
persist through midweek. An unsettled pattern with precip chances
and periodic restrictions may develop Thu-Fri but confidence remains
low.

&&

.CLIMATE...
RECORDS FOR 04-16

               MAX TEMPERATURE         MIN TEMPERATURE
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      87 2006     42 1905     62 1945     26 1943
   KCLT      89 2006     49 1890     64 1998     29 2008
                1896                    1991        1962
                                        1945
   KGSP      88 1888     54 1903     64 1945     24 1907



RECORDS FOR 04-18

               MAX TEMPERATURE         MIN TEMPERATURE
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      90 1896     44 1921     60 1927     28 1905
                                        1891
   KCLT      93 1896     45 1983     66 1896     32 2001
   KGSP      89 2002     51 1983     66 1927     28 1905
                1967

&&

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

&&

$$

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