Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 241807

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
107 PM EST Tue Jan 24 2017

Mild high pressure will build over our region from the south
through Wednesday. A cold front will move through the forecast
area early Thursday...bringing colder temperatures to the
region for Friday and the weekend.


of 1245 PM EST: A prominent upper ridge axis stretches from the
MS River Valley to the OH Valley this afternoon. At the surface, lee
troughing has set up just southeast of I-85. Profiles are quite dry
up the column and the only lingering clouds remain NW upslope flow
induced clouds near the TN border, and these should dry up quickly
through early evening. Anticipate the pressure gradient slackening
with time late today and winds becoming light tonight. Will shade
guidance toward the cool side overnight.

The upper ridge will be firmly atop the area around daybreak
Wednesday. Southwest flow return moisture in the pre-frontal RH band
approaching from the west will arrive in the western mountains by
late afternoon. Any slight chance PoPs for showers through late day
will be confined to mountain locations southwest of the Smokies.
Will nudge temperatures toward the warmer end of the envelope
Wednesday afternoon given recent model performance.


As of 235 AM EST Tuesday: An upper ridge over the area slides east
on Wednesday as an upper trough moves toward the area Wednesday
night. The trough flattens as it moves into the area Thursday and
Thursday night with the best short wave energy passing to the north.
That said, we do get a decent amount of forcing as short waves and
an upper jet move over the area.

At the surface, high pressure over the area Wednesday moves east
Wednesday night as a cold front associated with the upper trough
moves toward the area. Forecast remains dry Wednesday with highs 15
to 20 degrees above normal with the warm SW flow and high thickness

The front moves into the area Wednesday night and east of the area
Thursday. Despite the relatively narrow band of deep moisture and
quick movement of this system, high chance to likely PoP will be
featured given the forcing. QPF amounts will be relatively light.
Mid level thicknesses fall behind the front Wednesday night, but low
level thicknesses are slow to cool. Temps do get low enough across
the higher elevations for rain to mix with then change to snow
across the higher elevations of the NC mountains. Rain is expected
in the valleys and outside of the mountains. Lows will still be 15
to 20 degrees above normal.

Lingering moisture and NW flow across the mountains will keep
elevation dependent rain or snow showers going Thursday and Thursday
night. Any accums look to be limited to areas above 5000 feet and
should be an inch or less. Outside of the mountains skies clear as
moisture moves out and westerly flow develops. Windy to breezy
conditions will develop across the CWFA Thursday with diminishing
winds Thursday night. Highs Thursday will be near normal mountains
and around 5 degrees above normal elsewhere. Lows will be near to a
little below normal all locations.


As of 140 AM Tuesday...a return to winter at the end of this week
going into next week. A broad 500mb trough hangs over the eastern
part of our nation from Friday into early next week. On Monday, the
trough deepens over the Appalachians and becomes more narrow over
the East as the trough transits from west to east off the East coast
Monday night.

At the surface...high pressure over the West with low pressure over
Eastern Canada creates the pressure gradient bringing NW Flow snow
showers to the NC and TN border mountains. When comparing medium
range models, each has shortwaves moving through the flow from the
upper Mississippi Valley and Great Lakes region to the southern
Appalachians. There are some timing and intensity differences
between each model but the GFS shows a more intense final wave
coming through our area Monday with more snow showers under lower
atmospheric thickness values. A ridge axis reaches the spine of the
Appalachians on the GFS early next Tuesday while a nearly zonal west
to east 500mb flow develops early Tuesday on the ECMWF. Very little
instability shown in the models with only 50 CAPEs or less on the
GFS late Friday over far east TN and around 50 CAPE over TN and NC
mtns on Monday with the passage of the trough axis. This will
somewhat enhance snowfall rates.

Temperatures near or just below normal Friday with temps around 5 to
8 degrees below normal when the trough bottoms out on Monday before
pulling east.


At KCLT and Elsewhere: Developing lee troughing has generally been
unable to overcome WNW gusts with deeper mixing today, although some
adjustment to WSW flow is still likely this afternoon at KAND, and
possibly by very late afternoon elsewhere. Flow will finally back
toward southwest overnight and become light before increasing again
with mixing by late Wednesday morning. Some low end NW gusts at KAVL
will be possible well into the evening hours. For clouds, expect
little more than increasing FEW to SCT cirrus late in the period.

Outlook: Brief moisture return is possible ahead of the next cold
front Wednesday night into Thursday, with colder air and NW flow
moisture setting up through the weekend.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
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 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     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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