Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 241124

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
724 AM EDT Sat Jun 24 2017

Light showers will linger Saturday morning as the front slowly
crosses the area. Thunderstorms may redevelop later this morning
just ahead of the cold front over the piedmont and foothills.
Unseasonably cool and dry conditions will spread over the forecast
area in the wake of the front on Sunday and persist through the
middle of next week.


As of 700 AM EDT Saturday: Made several adjustments to pops through
the day with area of showers moving out of N GA toward the Savannah
Valley, and all guidance now pointing to increased pops across the
entire Piedmont this afternoon, working its way southeast with the
front. Temps and dewpoints look okay.  Other grid updates are for
aviation-related parameters.

Otherwise, remnants of Cindy are rapidly moving northeast; just in
the past couple of hours the closed circulation over WV has been
absorbed by the larger trough stretching down the Eastern Seaboard.
Initial band of convection has moved east into central NC, but as
the front continues to drop into the Piedmont today, should see an
increase in convection along it especially for the Upstate. While
deep-layer shear will be confined to the north, instability will
increase quite a bit today in the warm sector, especially with a
little cooling of temperatures aloft resulting in increased lapse
rates. High PW values around 2" will remain south of the front, so
with sbCAPEs progged between 1500-2000 J/kg but general lack of
shear, expect that really only damaging winds will be the threat
today (and lightning of course). New CAM guidance coming in has some
convection, perhaps some strong, developing across the NC Piedmont
through mid-afternoon, then blowing up convection across the Upstate
just after peak heating. Timing of the frontal passage will be
critical, because by this point the front is really trucking and
should be pushing quickly out by 00z.

With the high PWs, there remains the concern for isolated flash
flooding, especially with soil moisture remaining fairly high. Not
enough concern for a Flash Flood Watch but will have to be
monitored, but for now 12-hr QPF for today averages only about 0.5".

Temperatures today will be slightly lower than yesterday and below
seasonal norms, but with plentiful surface moisture in place to make
it feel nice and muggy. Improvement begins tonight though with
dewpoints dropping off and low temps near seasonal normals (instead
of 5 above), with the improving trend continuing into the short term.


As of 305 AM EDT Saturday: the short-term fcst picks up at 12z on
Sunday with longwave upper trofing moving across the Great Lakes and
steep upper ridging over the West Coast. The upper lvl pattern is
not expected to change much thru the period with the trof axis
remaining to our north and the ridge persisting to our west. By
early Tuesday, an upper shortwave will dig southward on the backside
of the upper trof providing increased upper-lvl divergence just
ahead of it. At the sfc, a lingering cold front will be located just
to our south to start the period. The model guidance is slow to move
the bndy farther south and offshore due to the persistent SLY flow
from the Bermuda High. By Monday afternoon, what`s left of the bndy
has finally moved offshore as the Canadian High slides SE and
towards our area. As for the sensible fcst, there is only some brief
slight chance PoP over our southeastern-most zones Sunday afternoon
with the rest of the period expected to be dry. Temps will be
slightly below normal for late June.


As of 225 AM EDT Saturday: the extended fcst picks up at 12z on
Tuesday with a reinforcing upper shortwave digging southward on the
backside of a broad upper trof. The axis of the shortwave will move
over the fcst area Tuesday afternoon and then lift NE by early Wed.
As it does, heights begin to rebound as upper ridging begins to
build to our south and persist over the region into the weekend. At
the sfc, broad high pressure will be centered just to our NW by
early Tuesday with below normal temps over the region. The high will
slide SE and over the fcst area early Wednesday and then slide off
the Atlantic Coast on Thursday. This will put the CWFA back under
warmer and more moist SLY low-level flow for the rest of the period.

As for the sensible wx, the period should be mostly dry with some
slight chance PoPs for Tuesday afternoon/evening and some slight to
solid chance PoPs for Thurs and Fri when we get back under more
moist southerly flow. Temps and dewpts will start out well below
normal and steadily warm thru the period with values reaching
climatology by the end of the work week.


At KCLT and elsewhere: MVFR to borderline IFR continues across
the Upstate TAFs, with a finger reaching toward KCLT and up to KAVL,
warranting a TEMPO for the next hour, but expect improvement in cigs
through the morning hours. Another round of convection should fire
later today as the front approaches from the west, with best chances
for Upstate TAFs and KCLT this afternoon. Could see some gusty winds
in stronger TSRA and have added this to the TEMPOs for all but
KAVL/KHKY. Rapid clearing/drying expected after 00z. S/SW winds will
continue 5-10kt, veering SW and eventually NW as the front passes
(current timing at KCLT is 04z).

Outlook: The cold front will slide south of the area early Sunday,
with drier weather developing through most of next week.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       Med   72%     High  95%     High 100%     High 100%
KGSP       High  94%     High  90%     High 100%     High 100%
KAVL       High  94%     High  95%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High  94%     High  85%     High 100%     High 100%
KAND       High  89%     High  85%     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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