Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201424

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1024 AM EDT Mon Mar 20 2017

Dry high pressure will settle over the Southeast states today. A
cold front will approach the forecast area Tuesday into Wednesday,
increasing chances for rain and thunderstorms. Cooler air will
return behind the front to end the work week before another frontal
system approaches the area next weekend.


As of 1020 AM: No significant changes; fcst on track. Cool and dry
high pressure will slide east of the area today under NWLY flow
aloft. Return flow around the high will set up atop the CWFA by
this afternoon, helping temps rebound to normal or slightly above
normal. Skies should be mostly sunny overall and winds light, making
for a pleasant day. With satellite imagery revealing mountain wave
rolls starting to form as moisture spreads in from the west, sky
cover grids have been adjusted to feature a little more cloudiness
over the higher mountain elevations.

Tonight, a broad long wave upper trough will begin to dig across
the Great Lakes, while a short wave ridge axis shifts east of the
forecast area. A weak wave of low pressure crosses the Central
Plains to the Ohio Valley, lifting a warm front thru the area early
in the evening. Some shallow moisture within westerly low-level
flow will bump up against the NC mountains overnight, which will
increase cloud cover and bring a chance of showers. The GFS and NAM
both have quite a bit of MUCAPE within this moist layer, and enough
bulk shear to support a thunderstorm complex upstream across the
Ohio Valley.  The 00z CAMs all seem to hint at some sort of MCS
(though doesn`t look to be severe in the simulated reflectivity)
developing in the southern Great Lakes, then dropping southeast
into the Central Appalachians overnight. It looks like the bulk
of whatever develops upstream will stay north of the CWFA. I will
forecast a chance of showers and slight chance of thunder along
the TN border counties after midnight. There is even some MUCAPE
east of the mountains, but I don`t think the convection will have
enough forcing to make it all the way across. So will keep most of
the Piedmont dry thru daybreak Tuesday. Temps will be well above
normal with increasing clouds from the west.


As of 325 AM EDT Monday: A pattern change is in store for the short
range as short waves dig an east coast trough through Wednesday. The
trough slides off shore Wednesday night as a ridge moves into the MS

At the surface, a cold front slides south into the area Tuesday as a
wave of low pressure moves east along the front and into our area.
Convective activity will develop to our west and slide into our area
during the day and into the evening. Moderate instability develops
across the area as relatively steep mid level lapse rates move in
and the large low level warm nose erodes. Strong unidirectional bulk
shear moves in during the afternoon as well. The storms could form
into a convective complex to our west before moving in, increasing
the organization of the storms and the potential for severe storms.
SPC has the mountains and foothills of the Carolinas and NE GA in a
marginal risk area for severe storms. This is very reasonable based
on all the parameters.

Convective activity moves quickly east Tuesday night with high
pressure nosing in and pushing the front south of the area. Some
showers will linger along the front as it moves south Wednesday with
precip ending Wednesday night as drier air moves in.

Highs Tuesday will be around 15 degrees above normal, but short of
record territory. Lows Tuesday night will be 10 to 15 degrees above
normal. Highs Wednesday drop to near normal with lows Wednesday
night around 5 degrees below normal, bringing frost/freeze concerns
back to the area.


As of 355 AM EDT Monday: The guidance is in pretty good agreement
for the medium range. An upper ridge moves into the area from the
west Thursday and Friday, then slides off shore Friday night as a
closed low moves into the mid MS valley. The low slowly moves east
Saturday reaching either the Great Lakes or the Southern
Appalachians by the end of the day Sunday.

At the surface, high pressure starts the period nosed into the area
in a cold air damming pattern. The center of the high slowly slides
off shore by Friday night. A southerly flow develops between the
departing high and the surface low pressure associated with the
upper low moving into the mid MS valley which may bring some upslope
showers by Friday night.

The surface low follows the tracks of the afore mentioned upper
lows. Either way, precip chances increase Saturday and maximize
Saturday night and Sunday as deep moisture and forcing move into the
area. Both tracks also show the potential for thunderstorms.

Temps fall back below normal Thursday with the high moving in,
keeping frost/freeze a concern Thursday night. Temps return above
normal by Saturday and Sunday.


At KCLT and Elsewhere: Not much change from the 06z TAF. Still
expect VFR conditions thru 12z Tuesday, as dry high pressure slowly
traverses east. Winds will remain light, shifting from N/NELY to
S/SWLY around 15z, except closer to 20z at KAVL. Otherwise, expect
just a gradual increase in cirrus this afternoon into tonight.
Isolated to scattered showers and thunderstorms are expected to
develop across the Ohio Valley this afternoon and track toward the
NC mountains tonight. However, the activity should diminish before
crossing the mountains. So no precip mention will be carried in any
of the TAFs.

Outlook: A cold front may bring showers and perhaps a few
thunderstorms on Tuesday, possibly into Wed. Brief drying is
expected Thursday, while moisture should begin returning by the end
of the week.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
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  95%
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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