Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 250706

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
306 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.


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 and Elsewhere: Upper cloud shield will prevail thru most of
the period...while MVFR CIGS develop in good llvl Atl moist flux
this morning. A strong subs inversion will keep MVFR cigs trapped
thru the morning most locales with heating lifting cloud bases to
VFR quickest at KCLT arnd 15z-16z. An occluded frontal system
approaches the region tonight and isent -shra will develop along an
attendant warm front. Have prob30s all sites except KCLT aft 01z-02z
thru the period. Winds will remain s/ly to ssw/ly along the wrn edge
of a sfc ridge reaching moderate levels with perhaps some low end
gusts by mid-afternoon.

Outlook: Areas of precip will continue thru 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...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High 100%     High  98%     High 100%     High 100%
KGSP       High  98%     High  90%     High 100%     High 100%
KAVL       High 100%     High  98%     High 100%     High  92%
KHKY       High 100%     High  96%     High 100%     High  98%
KGMU       High  97%     High  82%     High 100%     High 100%
KAND       High  85%     Med   72%     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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