Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 150536

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1236 AM EST Fri Dec 15 2017

Dry and cool high pressure will dominate our weather through Sunday
morning. Weak southerly flow with limited moisture will return to
the area Sunday and Monday as another cold front approaches from the


130 AM EST Update...No sigfnt changes needed to the going fcst. Adj
hr/ly temps up a bit where winds have kept the shallow BL mixed.
Still expect mins right arnd freezing over the Upstate and NE GA
with below freezing temps north.

As of 1000 PM Thursday: Senisble wx for the overnight hours is
expected to be limited to increased cloudiness, in the form of
stratocu for portions of the mountains, and considerable cirrus
elsewhere as high clouds along and south of encroaching upper
jet axis rotate into the cwfa.  The temperature fall this evening
has been a bit slower than expected, and with considerable clouds
expanding across the region, have made an upward nudge to Friday
morning minimums. Later Friday, elongated positive tilt vort axis
will sweep acrs the cwfa, displacing higher level moisture
downstream of the region as the afternoon wears on. Post cold
frontal air will only support max temperatures 8-10 deg F cooler
than Thursday`s readings.


As of 215 PM EDT Thursday: A split flow pattern will set up over the
southern half of the CONUS by Friday evening, with a northern stream
clipper system moving from the southern Appalachians to the mid-
Atlantic/southeast coast while deep, closed low pressure sets up
over Mexico. Dry profiles will persist over our forecast area
through Saturday as a flat upper ridge develops over the southeast,
with temperatures near climatology. Meanwhile, the southern tier
system will open up and phase through west TX. This system will lift
over the Ohio Valley through Sunday as yet another southwestern
cutoff low develops somewhere from Arizona to the Baja Peninsula.
Mid level moisture will begin returning from the southwest ahead of
the first phasing system Saturday night, but any deeper moisture
will be slow to arrive through Sunday. Any early Sunday morning
onset of light precipitation in the far southwest mountains could be
freezing rain, but onset prior to temperatures warming above
freezing looks unlikely.


As of 235 PM EST Thursday: Guidance is coming into better agreement
on the overall pattern through the medium range. However, some
detail differences remain keeping the overall forecast confidence on
the low side. Upper ridging over the southeast CONUS Monday moves
east Tuesday as split stream troughs move east toward the area. The
GFS is faster with the troughs keeping both streams relatively in
phase and moving east of the area Wednesday. The ECMWF moves the
northern stream trough to the east with similar timing as the GFS
but is slower with the southern trough and actually has a secondary
southern stream trough late on Wednesday. The GFS troughs, while not
particularly strong, are stronger the troughs on the ECMWF. A wave
forms along a frontal boundary stalled to our south Monday which
spreads moisture and precip north into the area. A stronger cold
front moves into the area Tuesday and to the east Tuesday night.
This should bring a better chance of precipitation, but even that
could be limited as moisture flux may be interrupted by convection
along the stalled front to our south. Therefore, have limited highest
PoP to good chance given the uncertainty. Looks like precip will be
all rain as H85 temps and thicknesses are warm for this time of
year. Some mountain valleys could be in the 30s but should remain
above freezing throughout. There could be some lingering NW flow
precip Tuesday night across the mountains, but even this ends before
temps cool enough for snow to mix in. Temps should be above normal
all locations.

Dry high pressure and upper ridging build into the area Wednesday
and Thursday. Another trough and frontal system build over the
middle of the CONUS by late in the period, but expect any precip to
hold off until after this forecast period, especially since there is
timing disagreement with this system. Temps cool a little but remain
above normal.


At KCLT and Elsewhere: VFR conds thru the TAF period at all sites. A
weak sfc bndry will be forced northeast as a strong ulvl jet core
traverses the area. No good chance of precip with this feature as
soundings show dry air thru the column. It will be hard to get clouds
outside of passing Ci...but a few higher based Cu may develop east,
including CLT, closer to the bndry. Winds will remain rather weak
and back ne/ly to nw/ly over the non/mtns and a little stronger
while channeled nw/ly at KAVL.

Outlook: Potential for short-lived restrictions on Sunday with rain
showers. Otherwise, expect VFR as a series of dry cold fronts move
through the area.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  81%     High  82%     Med   68%     Low   56%
KGSP       Med   70%     Med   75%     High  83%     Med   64%
KAVL       High  94%     High  85%     Med   70%     High  87%
KHKY       High 100%     High  83%     Med   66%     High 100%
KGMU       Med   76%     High  86%     High  85%     Med   63%
KAND       Med   76%     Med   65%     High  90%     Med   61%

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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