Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 180547

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1247 AM EST Sat Feb 18 2017

A weak upper low moves east today across the southeast states,
reaching the Carolinas tonight then off the Carolina coast Sunday.
The full effects of a strong upper ridge moves in to start the week
with much above normal temperatures. Another period of light
rainfall is possible mid week as a weak upper trough moves through
the region. A cold front approaches at the end of the week with
possible showers and thunderstorms.


As of 1245 AM EST: A closed upper low center moving into western
Arkansas early this morning will open up over the mid MS River
Valley today and cross the Appalachians tonight. The deepest
moisture ahead of the lifting system will cross the forecast area
mainly from mid morning through mid afternoon, but with the
precipitation band encountering increasingly dry air as it lifts
northeast and outpaces the upper forcing. This will lead to a fairly
sharp PoP gradient ranging from low end likely across the far
southwest NC mountains to sub slight chance east of I-77. A similar
maximum temperature gradient will result, with the driest eastern
piedmont locations possibly approaching 70 again for highs.

W to NW upslope flow moisture will continue along the spine of the
southern Appalachians tonight, possibly enhanced by the passing
upper trough axis. PoP should shut off quickly east of the mountains
this evening, but low end shower chances will only gradually pare
back toward the TN line overnight. Patchy fog will likely develop
overnight as mid level drying wraps in atop a slightly moist
boundary layer, with temperatures in the 40s everywhere but the
higher mountain ridges.


At 200 PM EST Friday...On Saturday evening upper ridging will be off
the East Coast and over the Great Plains, while a weakening upper
low will be crossing TN. The low will move across the Southern
Appalachians overnight, with the bulk of vorticity rounding the base
of the trough over Southern GA and Northern FL. As the low moves off
the coast on Sunday, and upper ridge will cross the MS River Valley,
reaching and then the Gulf States and Western Great Lakes. By Monday
the ridge reaches the Southern Appalachians while an upper trough
crosses the Great Plains.

At the surface, on Saturday night moisture associated with the upper
trough will be spreading across the Southern Appalachians, while
moisture associated with a weakening surface front crosses FL. On
Sunday moisture will decrease east of the mountains as the upper
trough moves toward the East Coast, resulting in decreasing
precipitation. Rainfall totals will be rather light. Sunday night
and Monday feature dry high pressure spreading across the down the
Easter Seaboard. Temperatures will run well above normal.


As of 230 PM EST Friday:  The medium range fcst period initializes
on Monday evening amidst a rather amplified upper pattern
highlighted by sharp ridging across the east, while sharp troughing
by way of phased northern/southern stream waves moves atop the
Plains into the MS Valley.  At the surface, expansive northeast
ridging will extend down the seaboard, while two distinct surface
cyclones are prevalent beneath the aforementioned upper waves.
Overall pattern evolution through the period hasn`t changed all that
much from previous fcsts as it pertains to the midweek cold front
and southern stream closed H5 low, however guidance solutions are
starting to converge.  Therefore, it currently looks as if a the
H5 ridge along the eastern seaboard will be compressed/flattened
thanks to the eastward track of the northern stream wave, while the
associated cold front progresses through the Mid MS Valley into the
OH/TN valleys by mid/late day Tuesday.  Furthermore, the surface
anticyclone will begin to shift southward as the best region
of upper confluence does the same thanks to the aforementioned
modification of the upper ridge.  At the same time, the southern
stream wave will have closed off as it tracks through the northern
Gulf before shifting to a more southeastern track across southern
FL into/through Wednesday.  The cold front mentioned above is
expected to move into Northeast GA and the Western Carolinas at
the same time where light precip is already expected by way of
upglide/upslope forcing thanks to southerly moisture advection
enhanced by the Gulf low.  Moving into Thursday, guidance favors
a slowing, perhaps stalling front across the Carolinas, while the
Gulf low actually looks to open and lift northeast toward Bermuda
which will effectively weaken the subtropical surface high.
Given the proximity of the stationary/quasistationary frontal
axis, precipitation chances will remain somewhat elevated from
this point forward.  Lastly, another upper wave looks to dive
out of Canada into the Plains by weeks end, which combined
with pronounced surface cyclogenesis will setup a rather robust
trough/front axis across the Central CONUS.  As a result, ample
southerly flow will prevail atop the southern states leading to
the possibility of a rather convectively active Friday/Saturday.
In general, the fcst will initialize dry before pops increase to
the chance range across the entire fcst area on Wednesday, lowering
to slight chances on Thursday before increasing yet again through
Friday into Saturday.  Temperatures are expected to remain nearly
2-3 categories above normal.


At KCLT and elsewhere: It is questionable whether any light
rain/showers can reach the ground across the forecast area as
moisture ahead of the approaching upper trough encounters dry air in
place across the terminal forecast area today. Light rain shower
chances look best midday from KAVL to KAND, but otherwise expect
mainly VFR level ceilings. Light southwest flow will continue
throughout the region, turning NW at times at KAVL.

Outlook: Expect dry and VFR conditions through early next week.
Another system may bring chances of precipitation and restrictions
to the area Tuesday into Wednesday.

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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