Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 230002

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
802 PM EDT Fri Sep 22 2017

Drier and stronger high pressure will develop over the weekend and
persist through at least the middle of next week. In the meantime,
Tropical Cyclones Jose and Maria will remain off the east coast.


As of 745 PM: A few showers and tstms still bubbling up across the
western and central NC mountains, but should dissipate fairly
quickly over the next couple hours. Skies are clearing out and winds
are light with temps still warm early this evening. No significant
changes were needed with this update.

Otherwise, a somewhat blocked pattern persists over most of the
eastern CONUS; an anticyclone extends from Texas to the Great Lakes,
but is undercut by a weak upper low over the Southeast. At the sfc,
high pressure centered to our north continues to drive a light
northeasterly flow into the CWFA. The pattern progresses a tiny bit
tonight, as the high starts to push east into the NE CONUS, and the
low retrogrades slightly toward the central Gulf Coast. Vort lobes
on the periphery of the low may bring some patches of high clouds
through the area, but skies should be mostly clear. Crossover temps
are expected to be reached in some areas of the Piedmont and so
patchy fog is expected; the mountain valleys should fog easily
particularly where rain falls nearby. Min temps will be similar to
the previous morning.

The increased influence of the ridge should allow for deeper mixing
and slightly drier sfc conditions that accordingly will reduce
instability. PoPs hence are lower and limited to the NC mountains
and far NE GA. Max temps will be largely unchanged: in the upper
80s across the Piedmont, and lower 80s in the mountain valleys.


As of 150 PM Friday: Upper ridging builds south into the area from
the Great Lakes and mid-Atlantic on Sunday and remains through
Monday although it does weaken. Surface high pressure follows a
similar pattern while Maria moves north well off the GA and SC
coast. The result will be a dry northeasterly flow keeping stable
air over the area. Despite the NE flow, thickness levels remain high
keeping highs around 5 degrees above normal each day. Fair skies and
the drier air mass will allow temps to fall overnight, but lows also
remain around 5 degrees above normal each morning.


As of 215 PM EDT Friday: the extended fcst picks up at 00z on
Tuesday with steep upper ridging in place across the Eastern CONUS
and deep trofing over the west. Over the next few days, the upper
trof will move eastward and begin to suppress the ridge as the
remnants of Tropical Cyclone Maria remain off the Carolina Coast. By
the end of the period next Friday, the upper trof axis is expected
to be over the region or just to our west. At the sfc, broad high
pressure will persist over the region thru most of the period. As
previously mentioned, TC Maria is expected to remain just off the
East Coast and not have a significant impact on the fcst area. A
fairly robust looking cold front will approach the CWFA from the NW
by early Thurs and likely move thru the CWFA by the end of the
period on Fri. As for the sensible wx, no major changes were made to
the fcst with mostly dry conditions expected. Temps will remain well
above climatology thru most of the period with a noticeable cool
down by day 7.


At KCLT and Elsewhere: High pressure and summerlike conditions will
be the norm again this period. Like usual, low VFR cu and convection
will dissipate quickly this evening. Winds will be generally light
and VRB overnight, but should prefer N to NE. Mountain valley fog
should develop again overnight, but confidence in restrictions at
KAVL are medium. Based on where rain fell near the airport and a
light NE possible, I do expect at least some IFR or lower vsby
and/or cigs. The rest of the sites look to be VFR, with some patchy
MVFR vsby possible in the usual fog-prone areas across the piedmont.
On Saturday, northeasterly low-level flow will bring some drier air
and keep convection limited to mainly the western NC mountains. So
no precip mention will be carried at any of the sites with this set
of TAFs.

Outlook: Precip chances will wane over the weekend and early
next week. With clear skies and calm conditions, fog and/or low
stratus are likely to return in the mtn valleys each of the next
few mornings.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High  89%     High  97%     High 100%
KAVL       High  97%     Low   46%     High  89%     High 100%
KHKY       High  97%     High  83%     High  94%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High  89%     High  91%     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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