Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 200229

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1029 PM EDT Tue Sep 19 2017

A weak trough will cross the forecast area from the west tonight
and tomorrow. Broad high pressure will then return over the region
for Thursday and Friday, with more moisture in the easterly flow.
Drier and stronger high pressure will settle over the region during
the weekend as both Hurricane Jose and Maria remain well offshore
in the western Atlantic.


As of 1025 pm: Water vapor imagery indicates a shortwave trough over
the Ohio Valley this evening, with a small surface reflection
extending through the Mid-South into Alabama. Associated area of
disorganized showers and storms essentially evaporated over the
southern Appalachians earlier this evening, and local radar imagery
is echo-free attm. Still would not rule out a stray shower or two
during the overnight, as depicted in some mesoscale/CAM guidance
output, but the threat does not appear to warrant a mentionable pop.
Min temps should be a bit warmer than last night given more cloud
cover. Patchy fog again is expected in the mtn valleys and foothills.

The axis of the shortwave will arrive in the area tomorrow morning,
maintaining fairly good lapse rates aloft and perhaps enhanced
lift via DPVA. Model consensus indicates SBCAPE values will near
1000 J/kg in parts of the area. Deep layer shear is not indicative
of severe threat, though showers and storms may cluster similar
to how they are behaving in the Ohio Valley today. Slight-chance
to chance range PoPs are included for the whole CWFA. Max temps
will remain quite warm, in the mid to upper 80s in the Piedmont
and lower 80s mountain valleys.


As of 220 PM EDT Tuesday: A weak upper trof over the area Thursday
closes off into a weak upper low Friday. Weak short waves rotate
through the trof and around the upper low both days. At the surface,
weak high pressure remains centered over the central Appalachians
through the period. A weak lee trof develops Thursday then
dissipates Friday. Low level moisture remains relatively high
Thursday then increases slightly Friday on developing easterly flow.
Mid level lapse rates remain relatively steep as well with cooler
mid level temps from the trof and upper low. The result of all this
is increasing chances of generally diurnal convection each day. Even
with overall better chances Friday, the mountains have the best
chance both days where LFC values are lower and low level
convergence better. Highs 5 to 10 degrees above normal Thursday drop
a few degrees Friday. Lows remain nearly steady around 5 degrees
above normal.


As of 205 PM EDT Tuesday: the extended fcst picks up at 00z on
Saturday with impressive upper ridging in place over the eastern
2/3 of the CONUS and steep upper trofing over the West Coast.
The trof will gradually slide eastward thru the period, however
the ridge will maintain its dominance over our region thru early
next week. At the sfc, very broad high pressure will be in place
to start the period. The remnants of TS Jose will still be
lingering off the New England Coast while TS Maria is forecast
to approach the Bahamas by early Sat. Maria is expected to remain
far enough off the east coast to not have any significant impacts
on our fcst area. We will remain under broad high pressure thru
day 7 with predominately dry, N to NELY low-lvl flow expected to
persist. As such, the sensible forecast is mostly dry with
temperatures about a category above normal through the period.


At KCLT and elsewhere: Am increase in low level moisture is expected
to result in better chances for cig/visby restrictions later tonight
and early Wed, although restrictions are expected to remain largely
confined to the mtn valleys. There is the potential for higher
clouds to linger and/or redevelop across the mtns later tonight,
perhaps before any lower cigs or fog forms, so confidence is not
extremely high in timing the onset and magnitude of restrictions at
KAVL, especially in light of the lack of any significant
restrictions there the past couple of mornings. Opted to forecast
prevailing MVFR conditions beginning at 08Z, with tempos for
2SM/SCT003 btw 09-12Z. Can`t rule out a restriction anywhere else,
but only KHKY receives a tempo for 4SM/SCT003 btw 10-12Z. A weak
surface front will slide into the area for tomorrow, bringing
improved chances for sct diurnal convection, and a PROB30 is
included at most sites during the afternoon. Otherwise, light/vrbl
or calm winds expected overnight, becoming W/SW again after

Outlook: Chances for diurnally favored showers and possibly a
thunderstorm will increase each day through the work week.  The best
chances look to be Thursday and Friday as flow veers easterly and
marginal moisture advection returns across the region.  That said,
the best chances for restrictions will be from early morning fog
across the northern NC Piedmont and foothills, as well as in the mtn
valleys. Drier weather appears returns for the weekend.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High  95%     High 100%     High 100%
KAVL       High 100%     High  91%     High 100%     High 100%
KHKY       High  95%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High  91%     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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