Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 251038

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
638 AM EDT Sat Mar 25 2017

Moisture will gradually return to the region today around offshore
Atlantic high pressure. Meanwhile, a low pressure system will lift
from the southern plains to the Midwest and push a band of moisture
toward the southern Appalachians. Deep moisture and persistent
southwesterly flow will set up over the southeast Sunday through
Tuesday with several rounds of showers and thunderstorms likely.
Drier air should return by the middle of next week.


630 AM EDT Update...No sigftn changes needed to the going fcst. Area
obs show low clouds hard to come by this morning with the exception
of the mtn valleys. A fairly thick Ci deck has kept localized temps
above the fcst curve and will adj in the grids.

An ulvl ridge axis will slowly shift east of the area thru the
period as h5 heights begin to fall across the wrn zones. An active
occluded system has developed across the srn Plains and this will
track to the NE...reaching the Midwest by 12z Sun. Meanwhile...good
difl flow aloft will engulf the FA and continue transporting thick
Ci over the area. There is some measure of llvl Atl/GOM rounding a
sfc ridge into the wrn zones and this will keep low clouds across
the mtns for much of the day. Most sites will experience few/sct low
clouds by the afternoon along with the prevailing Ci.

Not expecting much chance for precip until the better dynamical
forcing reaches the mtns and combines with llvl mech lift. Sometime
aft 03z still looks favorable for the onset of -shra...which will
increase in coverage north and east thru 12z. With little
instability and h5 vort energy remaining streamlined...a strong subs
inversion at h7 will not be overcome leading to relatively shallow
shower activity with no good chance of thunder. Qpf amounts will
thus be on the light side with the favored srn Transylvania and srn
Jackson counties receiving arnd 3/4 to 1 inch thru 12z. Max temps
today will likely reach a cat or so above normal as ssw/ly flow
continues. Mins will be held about 8-10 degrees above normal in good
cloud cover and continued llvl mixing.


As of 230 AM EDT Saturday: A negatively tilted upper trough will
stretch from the Midwest to the southern Appalachians on Sunday
morning, with all of the best associated upper forcing quickly
lifting northeast of the region through the day. However, a
persistent moist southwesterly fetch will continue across the area
Sunday through Sunday night. Thunderstorms will be possible
throughout the region, but the best instability should be draped
across locations southeast of I-85 Sunday afternoon. 40 kt of deep
layer shear will be in place Sunday, but with warm and moist
profiles limiting instability and the associated severe weather

Another upstream system will move from the plains to the Midwest
Sunday night through Monday, with the trough axis lifting across our
region Monday night. Fairly steep mid level lapse rates of 6.5 to 7
degrees C/km are expected late Monday into Monday night. SBCAPE
values are likely to peak in the 1500 to 2000 J/kg range late Monday
afternoon as dewpoints in the mid 50s or better persist while
maximum temperatures recover into the middle 70s in many locations.
Bulk shear values should be about half of what they were Sunday, but
with decent thermodynamics and stronger upper DPVA/jet divergence
forcing during peak heating. These ingredients may lead to isolated
severe thunderstorms Monday afternoon and evening.


As of 245 AM EDT Saturday: Surface low pressure passing north of the
forecast area on Tuesday will keep the southeast in a moist
southwesterly fetch through the day. There is some measure of
uncertainty over how quickly the passing upper trough will depart
east of the area, but chances look decent that some measure of
forcing will continue across eastern piedmont sections through mid
day on Tuesday. The best lingering thunderstorm chances will be
generally along and east of I-77. The trailing weak cold front will
then settle into the region from the northwest Tuesday night, and
possibly move just south of the area on Wednesday to bring in drier

Southeast ridging will continue through Wednesday night as another
closed low pressure system moves slowly eastward across west Texas.
The upper ridge will start to break down on Thursday, but the timing
of this remains somewhat uncertain given the spread in the handling
of the upstream system as it gradually opens up and phases back in
through late week. Nevertheless, a period of unsettled weather
should redevelop Thursday through Friday as moist southerly return
flow develops atop surface high pressure in a favorable location for
weak cold air damming. Confidence on the timing and placement of
PoPs, QPF, and instability for thunder is rather low given the
spread among the faster GFS/GEFS and the slower ECMWF. Will trend
the forecast cloudier late week with a return of chance PoPs for
showers as moist upglide gets reeastablished. Will feature slightly
cooler temps by Friday with weak cold air damming possible - at
least across the northern tier. Will follow the blended WPC solution
that leans toward the slower timing.


At KCLT: Upper level clouds will dominate thru most of the period.
Some VFR clouds will develop this afternoon...then VFR CIGS likely
aft 06z. Slow moving pre-frontal showers will develop to the west
late...but the terminal shud remain dry with lowering CIGS into the
MVFR range aft 10z.

Elsewhere: VFR conds this morning and afternoon at all sites except
KAVL where morning MVFR stcu will persist thru mid-morning. A
pre-frontal band of -shra will move into the mtns late and likely
reach KAVL arnd 02z. This area of precip will gradually shift east
thru the later period, warranting prob30s and prevailing -shra while
lowering flight conds into the MVR/IFR range.

Outlook: Areas of precip will continue Sunday likely creating
flight restrictions across all terminals. An unsettled and moist
pattern will persist next week and maintain the chances for low CIGS
and VSBY.

Confidence Table...

            10-16Z        16-22Z        22-04Z        04-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High  93%
KHKY       High 100%     High 100%     High 100%     High  81%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     Med   63%     High 100%     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:




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