Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 170550

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1250 AM EST Fri Feb 17 2017

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


As of 1240 AM EST: Water vapor satellite imagery shows a closed
upper system lifting slowly northeast across west Texas. A shortwave
ridge has developed downstream of this system and the ridge will
build over the southern Appalachians today. Some lingering cirrus
will be possible early today in the deep layer northwest flow aloft,
but this should thin as the ridge moves east and not otherwise mar a
very good insolation day. MOS guidance has been notoriously cool on
these good insolation days with some measure of 850 mb westerly
downsloping and general southwest low level return flow. Will thus
feature maxes some 3 to 4 degrees above MOS throughout, which will
be some 15 degrees or so above climo.

The H5 ridge axis will progress eastward tonight as the TX low
pressure system continues to open up and lift east over the
Mississippi River Valley. Any deeper returning moisture ahead of
this system should remain southwest of the forecast area through
daybreak Saturday. Min temperatures should rebound 1 to 2 categories
over Friday morning mins as mid and high level clouds return
overnight from the southwest.


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 baroclynicity, 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: Expect some lingering cirrus aloft in the
deep layer NW flow early today, but with high clouds thinning and
departing east through the day as ridging builds in from the west.
Low level flow will become more southwesterly with time, except for
continued NNW flow in the French Broad Valley at KAVL. Some low end
gusts will be possible this afternoon during the period of best
mixing, but these should be too infrequent and of low enough
magnitude to avoid mentioning in the TAFs.

Outlook: Spotty showers may move through the region Saturday into
Saturday night, but with the chance of restrictions highly
questionable. After that, expect dry and VFR conditions through
early next week.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
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:


Max temperatures have been raised about 3 degrees above MOS in most
areas, while dewpoints have been dried out a bit during the period
of best mixing this afternoon. This will lead to plenty of afternoon
RH values in the upper teens and lower 20s. With dry fuels, a Fire
Danger Statement may be needed in northeast GA. Elsewhere, we likely
will not have enough wind for more than a headline.




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