Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 011827

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
227 PM EDT Sat Oct 1 2016

Dry southwest flow will linger across the region through this
weekend. Progressively warmer temperatures are expected through
early next week. The path of tropical cyclone Matthew will be
closely watched as it tracks northward over the Eastern Caribbean
next week.


As of 2 pm ET:  Some mid-level cumulus over the mountains are the
only clouds around the area this afternoon.  These clouds will
dissipate after sunset.  Seasonally mild temperatures and light
winds are running close to previous forecast.

Main synoptic feature is the presence of an unseasonally large upper
low currently centered over Indiana with flow around it extending
down into the Gulf.  Surface low associated with the upper system is
located over Virginia with a stationary front extending southward
along the coast.  This pattern puts the GSP CWA behind the front in
a sector with drier air and far enough behind the low and front to
have light variable to southwesterly winds.  Water vapor and
analyses show pronounced dry slot over the area.

Upper low finally begins to make some northeastward progress into
the eastern Great Lakes through Sunday with a trailing trough
extending southward with some embedded shortwaves that rotate around
and across the CWA.  However, soundings are so dry that shortwaves
do not result in any precipitation, though some mid to high clouds
will result.  Boundary layer winds remain light southwesterly, becoming
northwesterly off the mountains on Sunday, with no moisture
advection in the near term.  Conditions will remain mostly benign
through Sunday with only the chance for a repeat of valley fog in
the early morning in the mountains.  Dry air mass will result in
morning lows on the cool side near CLIMO and highs warming to 5 to
10 degrees above seasonal normal.


At 200 PM Saturday: On Sunday evening an upper low will be crossing
the Eastern Great Lakes, with associated troughing extending
southwest to the Gulf Coast, and a high amplitude ridge upstream
over the plains. The upper low reaches Southern New England by
Monday evening, while the ridge upstream becomes positively tilted,
with its northern portion crossing the Great Lakes, the southern
portion remaining over TX, and a weak trough remaining over the
Gulf States. By Tuesday evening the upper ridge reaches the
Northeastern USA, and extends southwest down the Appalachians to the
Northeastern Gulf of Mexico.

At the surface, on Sunday evening a closed surface low will be
moving from Southern Ontario to NY, while the remains of a cold
front remains stalled off the East Coast, and modest moisture
spreads east across the Southern Appalachians. By Monday the surface
low moves offshore, and high pressure ridging spread down the
Eastern Seaboard, with limited moisture existing over the boundary,
and the surface front remaining offshore. This pattern persists
through Tuesday. With high pressure spreading over our from the west
resulting in a warm nose aloft, little or no upslope flow into the
Blue Ridge, and a lack of isentropic upglide over the surface ridge,
support for convection or precipitation is minimal. Temperatures
will run above normal.


As of 2 PM Saturday: the medium range fcst picks up at 00z on Wednesday
with steep upper ridging in place over the Eastern CONUS and a broad
and deep upper trof over the west. At the same time, Tropical Cyclone
Matthew is expected to be approaching the main Bahama Islands. The
overall model agreement wrt the upper level pattern is not very good
for the period. The latest 12z GFS is not nearly as progressive as the
older 00z run of the ECMWF. The ECMWF is faster moving the upper trof
eastward and thus pushing the upper ridge offshore. It has the trof
axis lifting to our NE by Friday afternoon while the GFS has the trof
axis still over the Great Plains. The GFS also brings TC Matthew right
along the Carolina Coast while the ECMWF keeps the system well offshore.

At the sfc, broad high pressure will be centered over far NE New England
with a wedge type pattern in place over the Carolinas. This pattern
is expected to maintain itself thru Thursday as TC Matthew approaches
the region from the south. From this point onward, the models diverge
considerably wrt the sfc pattern. The ECMWF keeps Matthew well offshore
and brings a cold front to the CWFA by early Friday, while the GFS moves
Matthew northward along the Atlantic Coast on Friday and Saturday. The
above mentioned cold front does not reach the fcst area until Sat
afternoon/evening with much drier Canadian high pressure spreading over
the region in the front`s wake on Sunday. As for the sensible fcst,
the consensus has been to put more weight/confidence in an ECMWF type
solution which keeps TC Matthew farther away from the the fcst area.
As such, I have only included slight chance POPs for the period with
most of these confined to Thurs and Fri. It will really depend on the
track that TC Matthew winds up taking. Temps should remain just above
climatology for most of the period.


At KCLT and elsewhere, conditions will be good VFR through Sunday
with dry air in place across the region behind a stationary front
off the coast.  Some weak mid-level shortwave energy passing through
the region on Sunday may generate some mid- and high-level clouds,
but is not expected to cause any precipitation.  With region well
behind main surface feature, winds will be light and variable with a
generally southwesterly direction over the Piedmont to northwesterly
over the mountains, and gradually veering on Sunday.

At KAVL/KHKY/mtn valleys: fog and low stratus may again develop in
mountain valleys, though models show less RH tomorrow morning than
this morning, and only included fog for the KAVL TAF.

Outlook: VFR conditions are expected in most places through early
next week as dry high pressure remains over the area.

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  93%     High  95%
KHKY       High 100%     High 100%     High  97%     High  97%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High  97%

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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