Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 200526

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1226 AM EST Sat Jan 20 2018

Cool high pressure will gradually move offshore this weekend giving
way to a warming southerly flow of air. A cold front arriving from
the west will bring precipitation to the region early next week,
with drying following through mid-week.


As of 120 AM EST Saturday: No major changes made to the fcst.
Some tweaks were made to hr/ly temps and td/s with notably
cooler conds across the NC mtn valleys. Overcast stcu is
approaching the wrn mtns and will maintain slight PoPs along the
TN spine. Dropped NAM soundings still support a brief period of
-fzdz/pl arnd 12z.

As of 1015 PM EST Friday: Minor adjustments made to temperatures,
dewpoints, and sky cover to account for latest trends through the
next few hours, as the rest of the near term forecast remains on

An SPS remains in effect for black ice for tonight through into
Saturday morning for the western piedmont of NC and the northern NC

As cirrus continues to pass overhead tonight, temperatures continue
to drop as latest observations depict the latest values are closing
the gap between the larger range we saw earlier this evening.
Currently, low to mid 20s are being observed across the mountains,
with upper 20s/low to mid 30s across the northern foothills and NW
Piedmont, to lower 40s across the Upstate. Expect the downward trend
to continue overnight as temperatures are expected to settle into
the mid to upper 20s (near 30 across portions of the Upstate).

With sfc high pressure in place, latest analysis depicts a weak, dry
upper trough axis draped across the escarpment tonight as upstream,
within the split flow, an upper disturbance is expected to become
closed off and propagate across the Deep South overnight through
tomorrow. Of the guidance, the GFS/ECMWF solutions remain dry,
however the NAM continues to key in on available low level moisture
which, with the help of upslope flow, could develop light QPF along
the TN/NC border overnight into tomorrow morning. Kept with thinking
from previous forecast in that any light QPF that does make it to
the ground given the dry air aloft, would fall as freezing
rain/drizzle given subfreezing temperatures. Any chance of precip
across the higher elevations will quickly diminish through Saturday
late morning as conditions are expected to remain quiet through the
rest of the day with sfc high pressure in place. Expect afternoon
high temperatures to climb into the 50s (around 60 across the
Upstate), with upper 40s across the higher elevations.


As of 230 PM EST Friday:  The short term fcst period kicks
off on Saturday night amidst a weak H5 low moving atop the I10
corridor with shortwave ridging to the west over the MS delta
and a deepening trof further west atop the Rockies.  At the
surface, weak high pressure across the southern Appalachians
will be slowly meandering eastward while cyclogenesis occurs
over the plains beneath the aforementioned Rocky Mountain trof.
Pattern evolution into/through Sunday will highlighted by the
southeast ridge sliding over the western Atlantic allowing for
persistent southerly waa across the southeast states while the
Plains cyclone deepens further beneath a now closed upper low, all
setting up a nice zone of baroclinicity along the MS river valley.

A cold front associated with this system, will march east
into/through the MS valley on Monday morning while gradual waa
improves surface dewpoints eastward across northeast GA and the
Carolinas.  Guidance has converged nicely with regard to timing
of this frontal intrusion into the NC high terrain and northeast
GA by late day Monday, with perhaps some upsloping of moisture
amidst modest sly H850/H925 flow along the southern Blue Ridge a few
hours earlier.  From that point guidance favors an evening/overnight
fropa across the remainder of the fcst area, fortunately limiting
potential instability amidst a rather dynamically robust system.
That being said, higher elevations across the region could see some
impacts from high winds given the strength of the sly llj overnight
into Tuesday morning.  Thus the fcst will remain dry with above
normal temperatures favored through midday Monday.  At that point
pops will gradually ramp up from the southwest with high likely
pops favored regionwide at some point through the overnight hours.
Pops will taper sharply from the west toward daybreak Tuesday with
only slight chances included along/east of I77 as well as along
the TN line where a brief round of nwfs showers cannot be ruled out.


As of 215 PM Fri: The frontal precip is expected to depart the
area Tuesday morning; the already small chances for upslope precip
along the Tenn border look to taper off by midday given relatively
backed winds and diminishing moisture. Continental high pressure
will move into the Southeast behind the front, and should more or
less remain over the area through the rest of the work week. 850mb
heights rise steadily into late Friday per GFS/EC consensus. This
seems to offset the cold advection occurring within the high,
keeping temperatures at or slightly above normal. Pattern change
is supported by the GFS, EC, and Canadian by next weekend, as the
ridge sets up east of the area and we enter the warm sector of a
deep Midwest low; precip chances remain too low to mention until
after the end of the fcst period.


At KCLT and Elsewhere: No restrictions thru the TAF period all
sites. The atmos remains very dry thru a deep layer as an area of
upper forcing and moisture crosses south of area. A low level ridge
and sfc high pressure will maintain weak sfc winds aligned sw/ly
non/mtns and up-valley across the mtns today with decoupling
expected aft midnight. Some increase in llvl VFR clouds across the
mtns this afternoon while FEW/SCT Ci crosses from the southwest.

Outlook: Potential for MVFR Monday into Tuesday with an approaching
cold front. Otherwise expect VFR.

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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