Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 171931
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
231 PM EST Fri Feb 17 2017
The strong ridge of high pressure overhead will slide to the east
as a weak upper low crosses the Tennessee Valley and Carolinas
over the weekend, bringing chances for light rainfall to the
area. Another round of light rainfall is possible mid-week as
a weak upper trough moves through the region. Late next week,
moist southeasterly flow ahead of an approaching cold front may
increase chances for moderate upslope rainfall. High temperatures
will stay 10 to 15 degrees above normal through the period.
.NEAR TERM /THROUGH SATURDAY/...
As of 215 PM EST: Clear sky expected through the rest of the
afternoon. Temp trends have caught up to the fcst, so high temps
still look okay, topping out at 10 to 15 degrees or so above climo.
A progressive pattern in the srn stream will bring some changes
across the region over the next 24 hours. Fair weather should
continue tonight as the upper ridge axis moves overhead, supporting
weak high pressure. After the ridge axis moves east, increasing
high- and mid-level cloudiness after midnight will help to keep
temps above normal, at least over the western half of the fcst area.
On Saturday, the models suggest that precip will be slow to arrive
even as mid and upper forcing spreads up from the southeast. One
problem is that the upper low lifting out of the Srn Plains should
open up across the TN valley and take a more positive tilt,
lessening the strength of the forcing. The better low level moisture
and sfc-based instability remain well to our SW thru the afternoon.
Even isentropic lift looks relatively poor, with the only productive
layers being at mid-levels. Expect some areas of light rain or
sprinkles, but coverage of measurable precip will probably be fairly
low. Because of cloud cover, high temps will be merely ten degrees
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
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.
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
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.
.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: VFR through the period. Clear sky through the
end of evening ops, with SW wind this afternoon going light at
sunset. An upper wave will approach the region tonight with
increasing high to mid-level cloudiness toward morning on Saturday.
Wind at KCLT might go light from the WNW before daybreak because of
drainage, but should return to light SW by mid-morning. Low clouds
will invade from the W around midday, but bases should remain above
050 for the most part. Think light precip chance will remain to the
west through the end of the TAF period.
Outlook: Spotty showers may move through the region Saturday
afternoon into Saturday night, but with the chance of restrictions
highly questionable. After that, expect dry and VFR conditions
through early next week. Another system may affect the region
Tuesday into Wednesday.
19-01Z 01-07Z 07-13Z 13-18Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL High 100% High 100% High 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 for this afternoon, while dewpoints have been dried out a bit
during the period of best mixing. This will lead to plenty of
afternoon RH values in the upper teens and lower 20s. Given the dry
air and fuels, a Fire Danger Statement will be issued for northeast
Georgia with several hours of RH in the 20 to 25 percent range and
fuel moistures below 8 percent.
GA...Fire Danger Statement until 6 PM EST this evening for GAZ010-