Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 231911

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
311 PM EDT Mon Oct 23 2017

A cold front will move east of the area tonight. Drier and cooler
air will sweep into the region on Tuesday leading to possible frosty
conditions Wednesday and Thursday morning.  Dry conditions are expected
to persist through the remainder of the work week before another front
moves in next weekend.


As of 230 PM EDT: Severe storm and flood threat will maximize the
next couple of hours as a strong line of convection moves west to
east across the area. Strong shear and helicity along the line is
moving into an area of better instability ahead of the line.
Therefore, the watch is well placed and severe storms will be
possible across the watch area as the line moves through. Heavy rain
and any flood warnings will be most likely across the foothills and
mountains of NC and the northern Upstate where upslope flow is
maximized along the line of convection. Sustained gradient winds
have diminished across the mountains, so the wind advisory has
expired as scheduled. However, strong gusty winds are possible
through the afternoon with stronger winds possibly being brought to
the surface in the heavier rainfall. More trees may fall than
normally expected with these wind speeds given the saturated soils.

Once the line moves moves through, expect clearing skies and a wind
shift to the SW or W. Some clouds will linger through the night,
especially across the TN border counties. However, winds will
diminish through the evening in all locations. Could be some patchy
fog overnight if the winds go light enough. Lows will be a little
above normal.

W to NW winds increase with mixing Tuesday as the pressure gradient
only slowly relaxes between a departing cold front and building high
pressure. Lingering moisture along the TN border will keep clouds
and isolated showers across that area through the day. Elsewhere
expect mostly sunny skies. Highs will be near to a little below
normal as cooler air begins to move in across the area.


As of 210 PM Mon: A full-latitude trough will deepen over the
eastern CONUS Tuesday night and early Wednesday. The associated
sfc low will move north out of the Great Lakes while the cold front
moves east of our CWFA. Heights will continue to fall Tuesday night
as colder air filters into the area. Moisture appears unlikely
to be sufficient for much additional precip at that time. Winds
remain westerly as opposed to NW, limiting their ability to drive
precip along the spine of the Appalachians anyway. Thus only a low
slight chance PoP is included along the Tennessee border. Temps
will be cool enough to mention a changeover from rain to snow in
the highest elevations, though it is more likely the precip will
taper off before changing over. Near-freezing temps (2-3 categories
below normal) and small dewpoint depressions imply some possibility
of frost in the mountains Wednesday morning.

Skies will be mostly clear east of the mountains Wednesday,
though temps will remain several degrees below normal. Winds will
remain generally across the Appalachians. A secondary shot of
low-level moisture is suggested by some guidance Wednesday night,
when temps will dip even colder under lighter winds and still with
little cloud cover at higher levels. However, at the present time,
confidence is too low to mention any precip in this period; frost
may return to more of the area however. Max temps will begin to
rebound Thursday as the cold advection weakens or reverses and
under a modifying airmass.


As of 235 PM EDT Monday: the extended fcst picks up at 00z on
Friday with another upper trof digging down across the Eastern
Dakotas and Minnesota and steep upper ridging building over the
West Coast. Over the next couple of days, the upper trof will
amplify as it moves eastward. The trof axis will eventually
move over the fcst area by the end of the period late Sunday
into early Monday. At the sfc, lingering high pressure will be
centered over the region while the next cold front approaches
from the west. The long range models have the front moving into
the CWFA by late Sat with the latest GFS continuing to be about
12 to 18hrs faster than the ECMWF. By early next week, the front
is expected to be east of the CWFA with high pressure spreading
back over the area.


At KCLT and elsewhere: Line of convection is moving through the area
at this time. Ahead of the line is IFR cigs, VFR vsby, and gusty SE
wind. TSRA and heavy showers are occurring with the line along with
variably gusty winds. Behind the line is improving conditions but
gusty SW winds. Some LLWS is also occurring with the line. Have
taken these conditions and timed the movement of the line east
across the CWFA for the afternoon. Expect VFR with diminishing winds
this evening. Some fog is possible overnight, and have included MVFR
vsby in these locations. Any fog burns off quickly after daybreak
with increasing WSW wind and VFR clouds. KAVL the exception with S
wind becoming NW and remaining there through the rest of the period.

Outlook:  Drier and cooler conditions will build back into the area
behind a cold front through Thursday. Moisture will slowly return
ahead of another cold front toward next weekend.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High  84%     High 100%     High  99%     High 100%
KGSP       High  90%     High 100%     High  96%     High  96%
KAVL       High  85%     High  90%     High  86%     High  96%
KHKY       Med   76%     High 100%     High 100%     High  93%
KGMU       High  84%     High 100%     High 100%     High 100%
KAND       High  92%     High 100%     High  86%     High  93%

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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