Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 170236

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
936 PM EST Thu Feb 16 2017

A warming trend is underway as southerly flow returns to the area
underneath a strong ridge of high pressure.  A weak upper low slides
across the Tennessee Valley and Carolinas over the weekend bringing
light rainfall to the area.  Another upper low moves across the Gulf
Coast mid- to late next week with another round of light rainfall.
High temperatures will stay 10 to 15 degrees above normal through
the period.


As of 930 PM: Our weather looks increasingly benign over the next 24
hours as an upper ridge axis approaches from the west. Weak high
pressure centered along the northern Gulf Coast will move slowly
eastward. Winds will continue to diminish overnight as the
pressure/height gradient weaken. Sky should be clear tonight, which
should allow temps to fall off to near normal, or perhaps a little
below normal across portions of the NC and eastern SC Piedmont,
where many locations were already reporting calm winds. Fair weather
will prevail on Friday with high temps expected to be more than 10
degrees above normal.


At 200 PM EST Thursday...On Friday evening a upper ridge will extend
from FL to the Western Great Lakes, while an upper low will be over
OK. The ridge progresses off the East Coast on Saturday, while the
upper low reaches TN, and another ridge amplifies over the Great
Planes. The upper low crosses the Carolinas and GA on Saturday
night, moving off the coast on Sunday. The models show the best
vorticity rounding the upper low over Southern GA and Northern FL.

At the surface, on Friday evening moisture from the Gulf of Mexico
will spread north over the Lower MS River Valley, on the back side
of a surface ridge located between the Bahamas and Bermuda. This
moist inflow will spread east across the Gulf States on Friday night
while a surface low closes off over AR. This low moves east across
TN on Saturday, while associated moisture reaches GA and the Western
Carolinas. The upper low moves off the East Coast on Sunday, with
moisture decreasing in its wake. Precipitation amounts are expected
to be rather light. Temperatures will increase with time, from above
normal, to well above normal.


As of 200 PM EST Thursday:  The medium range forecast period kicks
off on Sunday evening amidst an amplified upper pattern highlighted
by the departure of a rather potent shortwave off the Carolina
coastline, while nearly full latitude ridging builds westward
across the Plains.  At the surface, high pressure will begin to
build across the Mid MS as well as the OH/TN Valleys allowing for
dry northerly flow along/east of the Southern Appalachians.  Pattern
evolution through the period will feature even more amplification
aloft as the upper ridge axis shifts east atop Appalachians by
Monday morning while a deep southern stream wave/trough strengthens
over the Rio Grande Valley.  With that, Gulf moisture will advect
northerly into the lower MS River Valley through Monday thus
increasing baroclinicity, all while the aforementioned east
coast surface ridge transitions northward across the Great Lakes
into southern Quebec leading to development of weak wedging.
Meanwhile, a northern stream upper wave will move into Ontario
with a surface cold front extending southward across the Plains,
which given pattern evolution into Tuesday looks to stall well
to the west, however likely flattening/weakening the high
amplitude east coast H5 ridge. As said ridge becomes suppressed,
the surface component is progged to shift southward along the
Mid Atlantic while the now closed Rio Grande H5 wave moves east
through the Northern Gulf. These two features will combine to
enhance Gulf/Atlantic moisture advection across the Deep South
through midweek, thereby warranting increasing precipitation
chances. Deviation in the model output is somewhat pronounced by
this point as it pertains to the track of the H5 low as the GFS
favors a stronger Atlantic offshore subtropical ridge which
will allow for a more northern/slower track, while ECMWF/CMC
favors hardly any ridging and thus a much more southern track
which actually takes the cyclone across Southern Florida. For
this fcst, leaned heavily on GFS favored pattern yielding robust
convective activity along the Gulf/Atlantic coastlines into
periods end as the cyclone moves eastward, with said convection
increasing uncertainty further north into Northeast GA and the
Western Carolinas. Thus, the fcst will remain dry through midday
Tuesday before pops ramp up to slight/chance levels regionwide
to round out the period with temperatures well above normal.


At KCLT and elsewhere: VFR through the period, with mountain wave
clouds expected to dissipate here in the next hour or two.
Otherwise, occl SCT/BKN high clouds are expected through much of the
period. Winds start out light from the NW, diminishing further
overnight, before returning from the S/SW by late Friday morning. SW
winds should increase to 7-11 kts by mid-afternoon.

Outlook: The next chance of restrictions looks to be late Saturday
as an upper disturbance approaches the area from the west,
continuing into Sunday morning. After that, most likely VFR until
perhaps Tuesday and Wednesday as moisture comes in from the Atlantic.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
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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