Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 250547

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
147 AM EDT Mon Sep 25 2017

Broad, dry high pressure will persist across the region through the
middle of week. Hurricane Maria is expected to remain off the East
Coast through mid-week. A cold front will sweep across the region on
Thursday, bringing drier and much cooler air to the area for
the end of the week and take Maria out to sea.


As of 140 am Monday:  A broad upper ridge over the eastern CONUS
makes gradual eastward progress as TC Maria moves north.  Maria will
remain off-shore and her impacts to the GSP area will be limited to
some slight enhancement of the northeasterly winds. SCT-BKN high
clouds from Maria will persist across much of the region through
tomorrow. Subsidence and relatively dry/stable air will yield a
pop-less forecast while temperatures will remain 5 degrees or so
above climo through the period.


As of 155 PM Sunday: The dry and unseasonably warm weather will
persist through the middle of the week, as high amplitude upper
ridging persists over the area. A combination of surface high
pressure centered over the northeast and Tropical Cyclone Maria
moving N toward the NC outer banks will support a sharp surface
ridge over the area, with northeasterly surface winds, which could
become somewhat breezy by the end of the period. Although moisture
may increase to some extent within the circulation around Maria,
especially over the Piedmont, showers would be very unlikely with
subsidence inversion remaining in place across the area. More likely
would be increased high clouds on Tuesday. Therefore, have continued
with the dry forecast. Temps 5 to 10 degrees above normal Tuesday
rise to around 10 degrees above normal Wednesday. That said, high
clouds Tuesday could keep temps across the I-77 corridor a degree or
two cooler than forecast.


As of 145 PM Sunday: For the period starting Wednesday evening,
Hurricane Maria is forecast to be just off the North Carolina coast.
In the mid to upper flow, a series of strong shortwaves are forecast
to cross mid to eastern Canada and Great Lakes region breaking down
the upper ridge which has been giving our region much above normal
temperatures.  The associated cold front crosses our area on
Thursday. With very little moisture accompanying the front, only
slight chance POPs in the forecast for portions of the mountains.
Height falls and cool high pressure will bring temperatures a little
below normal next weekend. Hurricane Maria will quickly be shifted
east and out to sea once the front encounters the tropical cyclone.
A secondary cold front is forecast to cross from the northwest late
Friday and Friday night. The combination of this secondary cold
front and possible development of a low along the primary front near
Florida could bring some rain to mainly southern areas Friday night
and Saturday.  By Sunday, cool high pressure centered over Illinois
will dry and cool weather into the start of next week.

Temperatures will start several degrees above normal Thursday then
drop to near normal Friday then a few degrees below normal through
the weekend.


At KCLT and elsewhere:  The main concern for this period will be the
potential for low stratus and/or fog in the mtn valleys and typical
cool spots outside the mtns later this morning, meaning that KAVL
and KHKY are the only real concerns in this regard. Dewpoint
depressions of two degrees at TAF issuance time do give one pause,
while light N/NE winds could bring any fog/low stratus developing
along the lake over KHKY toward daybreak. Having said that, it`s
certainly not a slam dunk that much will develop near these two
sites, as the boundary layer is relatively dry, and abundant high
clouds may slightly inhibit additional cooling. We did opt to
include some mention of restrictions at these two sites, but limited
them to MVFR w/in a tempo. Otherwise, VFR conditions are expected
through the period. Light NE winds will increase to around 10 kts by
late morning, diminishing again this evening.

Outlook: Dry conditions expected for the first half of the week.
Under mostly clear skies and calm conditions, fog and/or low stratus
are possible in the mtn valleys each of the next few mornings. A
mostly dry cold front will cross the region late in the week.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
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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