Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 190641

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
241 AM EDT Wed Oct 19 2016

Dry and warm high pressure will continue today into Thursday with
maximum temperatures once again flirting with record highs. A cold
front will cross the area Thursday night into Friday, increasing
rain chances mainly across the mountains. Drier and much cooler
conditions will set up across the area over the weekend. A mostly
dry front will approach from the north on Monday and settle south of
the region on Tuesday.


At 200 AM Wednesday: An upper ridge will progress across the
Carolinas and Georgia today and tonight, to the coast by Wednesday
morning, while a surface ridge beneath if weakens and drifts
offshore. Meanwhile, and upper trough will progress the Great Plains
and approach the MS River Valley. A surface cold front will reach
the OH and Mid MS River Valleys by Thursday morning. Gulf Moisture
ahead of this front is expected to remains to our west, limiting the
chance of precipitation through the night. Temperatures will run
above normal across our area under the upper ridge, challenging
record daytime highs.


As of 230 AM EDT Wednesday: A deepening central CONUS trough will
exit the southern plains Thursday morning and cross the MS river
valley Thursday evening. Downstream, a solidly warm sector airmass
will persist across our region on Thursday as S to SW low level flow
increases ahead of the approaching cold front. Pre-frontal moisture
may approach the southern Appalachians Thursday afternoon and
western mountain thunderstorms will be possible as SBCAPE values
rise to 500 to 1000 J/kg. There is then fairly good model agreement
on the trough axis moving swiftly eastward and crossing the base of
the southern appalachians with an attendant cold front Friday
morning. Any appreciable QPF will be confined to western mountain
sections and amounts should be capped at 0.5 to 1 inch even there,
with much less farther southeast. Any approaching instability just
ahead of the cold front should diminish as the boundary crosses the
region during the overnight hours into Friday morning. In addition,
the better low level wind shear will be just behind the frontal
zone, with just 25 kt or so of surface to 3 km bulk shear ahead of
the boundary. This should limit any severe weather potential.

Meanwhile, any tropical/subtropical development occurring over the
western Atlantic will stay well offshore Thursday through Friday
given the approach of the trough/front. A brisk NW flow gradient
will be in place across the southern Appalachians behind the front
Friday through Saturday. Trailing channeled shortwaves in the deep
layer NW flow will cross the region Friday into Saturday, but with
very limited deep moisture. Some measure of low level upslope
moisture will likely produce additional rounds of cloudiness and
possibly isolated showers in the northern mountain upslope areas.
Temperatures could get cold enough Friday night for a few flurries
to mix in along the higher ridges by daybreak Saturday but little or
no accumulations are currently expected. Winds on Friday through
Saturday will be quite brisk and gusts could flirt with advisory
levels during the peak of the cold advection. Morning winds should
preclude much of any frost, and only the highest mountain ridges
should see an advective freeze.


As of 240 AM EDT Wednesday...Heights will build from the west on
Sunday with ridging steadily returning to the eastern CONUS Monday
through Tuesday. At the surface, high pressure will migrate off the
southeast coast as a backdoor cold front approaches from the north
on Monday. The boundary should settle southward through the region
by Tuesday with high pressure ridging down from the north. Only
Monday should see above climo temperatures.


At KCLT and elsewhere in the Piedmont: VFR. Some low VFR cigs are
possible over SC sites this morning. Blended guidance supports a few
areas of daybreak fog, but not at TAF sites. Winds will favor the SW
overnight and during the day, backing to SE Wednesday evening. Model
time heights suggest the prevailing cloud deck will be at around
6000 ft, but actual coverage appears to be quite limited. Limited
moisture and a warm nose aloft will prevent convection from

At KAVL and the mountains: Valley fog is expected to form in the
predawn hours, severely impacting vsby at least periodically.
Midlevel cloud cover had already arrived form the southwest, but
LIFR cigs are expected with daybreak fog. Winds at KAVL will favor
NW early in the day before backing to SW and the SE. A lack of lift
and limited moisture will preclude convection.

Outlook: Warm and mostly clear high pressure will persist overhead
through Thu. Some mountain valley fog and low stratus may return
Thu morning. A front will move through Friday, bringing a period
of gusty winds and perhaps restrictions due to cloud cover as cool
autumn air pushes back into the region.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High 100%     High  97%     High 100%     High 100%
KGSP       High 100%     High  94%     High 100%     High 100%
KAVL       Med   60%     High  89%     High 100%     High 100%
KHKY       High  94%     High  94%     High 100%     High 100%
KGMU       High 100%     High  97%     High 100%     High 100%
KAND       High  97%     High  94%     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:



  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      83 1938     47 1891     61 1910     27 1976
   KCLT      87 1938     55 1976     66 1937     30 2009
   KGSP      87 1941     56 1976     65 2006     32 2009


  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      83 1985     42 1961     62 1950     25 1981
   KCLT      86 1926     49 1989     66 1993     30 1972
   KGSP      86 1899     50 1989     68 1894     29 1972




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