Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 221449

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1049 AM EDT Thu Mar 22 2018

Dry and unseasonably cool high pressure will dominate our weather
through Friday. The next low pressure system will cross the region
from the northwest over the weekend, with cooler and drier Canadian
high pressure building down over the area early next week.


As of 1040 AM EDT: cloud cover has almost completely dissipated
across the fcst area over the past few hours with only some
lingering stratocumulus over the higher terrain. Winds should
remain steady and out of the NW thru the day and into the evening
with speeds decreasing after about 00z or so.

Otherwise, with clearing skies on tap for today, so are warmer
temperatures compared to what we saw yesterday, with upper 50s across
the Upstate, mid 60s across the NW Piedmont, and cooler into the overall
40s across the mountains. These above freezing temperatures will
allow for snow to melt this afternoon, but with temperatures
expected to dip back into the 20s tonight, any water/residual snow
that did not evaporate with the gusty winds will refreeze. On area
roadways and elevated surfaces such as bridges and overpasses,
expect black ice to potentially become a widespread concern tonight
through into early Friday morning and motorists should use caution.
If the road/ground surfaces look wet, assume it is black ice. Across
the northern foothills and northern portions of the NC piedmont,
overnight temperatures will dip to near or just below freezing,
remaining a few degrees warmer across the Upstate.


As of 325 AM Thursday: A 500 mb closed low system over NY/PA on
Friday will move east off Cape Cod by early Saturday. Deep layer
northwest flow behind this system will persist through Friday
night, with mainly mid clouds moving southeast over the area to
keep temperatures on the cool side of climo.

The ridge over the southeast will flatten over the weekend as a
prominent wave drops from the upper Midwest to the central
Appalachians. Deeper moisture and better forcing will arrive from
the northwest on Saturday as isentropic upglide develops quickly
over the activating warm front. Mixed precipitation looks quite
possible along and north of I-40 in western NC Saturday
morning and will keep the forecast ptypes rain versus snow
for now. Saturday afternoon temperatures will be a good 10 to 20
degrees below climo across the norhtern tier and 5 to 10 below
climo in the south.


As of 335 AM Thursday: There is good model agreement on a vigorous
surface low moving from Missouri down the frontal zone to the
southern Appalachians Saturday. There is also good consensus on the
low system transitioning quickly to the coast on Sunday, with
cooler air spilling southward from dominant Ontario/New England high
pressure in damming fashion. Meanwhile, mid and upper drying will
quickly wrap from the west on Sunday, but low levels could remain a
bit moist as cooling occurs from the north in the developing cold
air damming. The ptype forecast for any slight chance to chance PoPs
will follow partial thicknesses methods.

The deamplifying wave will move off the coast on Sunday, with strong
ridging developing over the east Monday through Wednesday. The
primary difference between the GFS and ECMWF is that the GFS allows
the lower level moisture to linger through the period. The
preference is that the strength of the southeast ridge should
greatly restrict precipitation chances Mon through Wed, so will lean
toward the drier ECWMWF solution in this regard. Ptypes will
continue to follow partial thickneses for any slight chance weather.
Temperatures will transitions from minus 15 below climo on Mon
to a category above climo by Wed.


At CLT and elsewhere: Expect VFR to prevail through the valid TAF
period. FEW mid to high level clouds this morning will dissipate
giving way to clear skies today through into Friday morning with sfc
high pressure building in from the west. A tightened pressure
gradient will persist across the NC mountains through early this
afternoon, thus have kept gusts at KAVL through the morning hours.
Elsewhere, expect northwest winds 5 to 10 kts today, with low end
gusts returning through the afternoon. Gusts will subside this
evening, with winds becoming NNW and AOB 5 kts.

Outlook: Increasing precipitation chances and possible flight
restrictions are possible this weekend with another approaching
storm system. Otherwise expect VFR.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
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:


A drying trend is expected today across northeast Georgia as sfc
high pressure builds in from the west. With northwest winds of 10 to
15 mph and occasional gusts up to 20 mph this afternoon, along with
lowering relative humidity values, which are expected to drop to
between 20 to 25 percent, fuels will begin to dry out. Thus, a Fire
Danger Statement has been issued as the fire danger is expected to
increase this afternoon given the favorable environment.


GA...Fire Danger Statement until 8 PM EDT this evening for GAZ018-
NC...Wind Advisory until 11 AM EDT this morning for NCZ033-048>050-


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