Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 232056

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
456 PM EDT Sat Sep 23 2017

Broad high pressure will continue to build through the weekend and
persist through the middle of next week. In the meantime, Tropical
Cyclones Jose and Maria will remain off the east coast.


As of 430 PM: Just a quick update to tweak PoPs in the mountains,
where coverage is ticking up a bit. Still not expecting anything
more than showers and garden-variety tstms. Temps are on track.

So a fairly benign weather pattern will continue through Sunday as a
large eastern CONUS upper ridge makes gradual eastward progress
Surface high over the northeast CONUS with ridge running down the
Southern Appalachians changes little through tomorrow and will keep
the area in light northeasterly flow.  Neutral to very slightly
unstable surface air this afternoon is expected to produce a few
convective showers and possible thundershowers,
orographically-forced, over the mountains of western NC and
northeast GA (as depicted by CAMs), Nearly zero wind shear and low
instability will make these showers pulsatile, with low chances for
becoming severe.  Slight warming at mid-levels will eliminate this
rather limited level of instability, and no showers are forecast for

Temperatures have been running above guidance and model blends.
Current forecast was arrived-at by adding a couple degrees to broad
model blend.  This gives temperatures 5 to 10 degrees above normal
today and tomorrow.

Hurricane Maria continues to spin in the Atlantic, and is moving
down the axis of minimum deep layer shear towards the NC Outer
Banks. For Upstate SC and surrounding areas, Maria will do little
more than slightly enhance the northeasterly surface flow on Sunday.


As of 215 PM Saturday: Dry and unseasonably warm weather will
persist through the short term, as a highly amplified upper ridge
tightens its grip on the eastern Conus. The air mass is expected to
remain dry and stable early in the week, as a surface ridge
strengthens with the upper anticyclone gradually spilling east of
the northern/central Appalachians. That said, the official forecast
track of Tropical Cyclone Maria has slowly edged westward through
time. While there is good agreement that this increases the pressure
gradient between Maria and the surface ridge, possibly leading to
breezy conditions by Tuesday, there is disagreement on whether low
level moisture increases in this flow. If the moisture does increase,
then the atmosphere could become unstable enough for isolated
convection over the area. For now, have kept the forecast dry due to
the uncertainty. Also uncertain is the amount of any high clouds
that would move in from the east around the periphery of the
cyclone. Again, due to the uncertainty, did not lower the highs as
much as a model blend would suggest, but did drop them a degree or
so across the I-77 corridor. For now, this keeps highs and lows 5 to
10 degrees above normal.


As of 205 PM EDT Saturday: the extended fcst picks up at 00z on
Wednesday with the persistent upper ridge beginning to weaken as
a northern stream upper trof moves up and over the ridge from the
west. As we move into Thurs and Fri, the upper trof axis will
broaden and amplify over the Great Lakes and is expected to dig
farther southward and approach the fcst area by the end of the
period on Sat. At the sfc, high pressure will still be lingering
over the region on Wed as TC Maria remains just off the Carolina
Coast. Compared to previous fcsts, the trend has been to bring
Maria a bit closer to the Coast on Wed, and then move her farther
offshore later on Thurs. This newer scenario will likely result in
a less impressive overall fropa on Thurs. In the wake of the front,
cooler high pressure will overspread the region on Fri and linger
well into the weekend. As for the sensible wx, mostly dry conditions
are still anticipated, although the long-range models are showing
more moist NLY flow on Wed as Maria gets closer to the Carolina
Coast. Temps will remain well above climatology thru Thurs and
cool to below normal by Sat.


At KCLT and Elsewhere: Weather pattern will remain mostly benign
under an upper ridge with steady and light northeasterly winds and
some afternoon cumulus clouds near FL050 today and tomorrow.  Some
convective showers may occur over the mountains this evening, but
are not expected to reach any of the TAF sites. Only source of
restrictions will be the chances for fog at KAVL.  TAF represents
persistence with what has been occurring the last couple days with
shallow nocturnal valley ground fog that burns off around 14Z.

Outlook: Precip chances will wane through the weekend and early next
week. With clear skies and calm conditions, fog and/or low stratus
are likely to return in the mtn valleys each of the next few

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High  94%     High  85%     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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