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Area Forecast Discussion

FXUS62 KGSP 301750

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
150 PM EDT TUE AUG 30 2016

A weak tropical system will approach the North Carolina Outer Banks
today before moving back out to sea on Wednesday. A cold front will
approach the region from the north Wednesday night with another
tropical system emerging from the Gulf of Mexico on Thursday. This
system is expected to remain just to our south and move offshore
over the weekend. A Canadian air mass is forecast to build over the
region this weekend into Monday.


As of 130 PM...a few showers have developed over the Lakelands, so a
small precip chance will have to be nudged up a bit there. Temps
look good still.

Otherwise, a broad subtropical ridge will remain across much of the
southern 2/3 of the CONUS through the period, with a pronounced
weakness in the ridge persisting near the Southeast coast. The
cyclonic circulation around a weak upper level low near Savannah
will continue to spread ocnl sct high/mid clouds into the forecast
area through the period. The surface ridge over the area will
continue to support a relatively low theta-E air mass, which
combined with poor mid-level lapse rates will yield little in the
way of buoyancy across the rest of the area this afternoon. The
latest HRRR, which was more or less on the money in advertising a
convection-free forecast area yesterday, is painting a similar
picture for today. Nevertheless, it appears there will be a little
bit better instability near the TN border this afternoon, so a
slight chance for showers will be advertised there. Elsewhere, with
the exception of the Lakelands, chances for convection through
tonight are less than 20 percent.

Little change in temps is expected through the period, and forecast
maxes will be advertised very similar to yesterday, maybe 1/2 a
degree warmer in some areas. Min temps tonight will be a little
above climo.


As of 200 AM Tuesday: On Wednesday, a weak H5 low is forecast to be
centered over southern GA/SC around sunrise, lifting across the
midlands and becoming absorbed in the longwave trough during the
afternoon. Tropical Disturbance nine will likely remain off shore of
the Big Bend area of FL through Wed evening. The 0z GFS indicates
that moisture will deepen across the CWA as a cold front pushes into
the Ohio River Valley. Forecast soundings from the NAM indicate that
the region will remain weakly unstable through Wednesday afternoon.
I will forecast Sct SHRA/TSRA across the mtns, with iso coverage
across the foothills and Piedmont. High temperatures should range
from the mid 80s within the mtn valleys to near 90 east.

Thursday should see the greatest coverage of SHRA/TSRA through the
short and extended periods. The 0z GFS shows the axis of the H5
trough sliding across the southern Appalachian region during the
heat of the day. At the sfc, a weak cold front is expected to sweep
NW to SE across the CWA. Deeper moisture and cooler mid level
temperatures may yield CAPE values between 1500-2000 J/kg along and
ahead of the front. I will forecast an afternoon peak in PoPs,
ranging from likely over the ridges to 30-40 percent across the
foothills and Piedmont. High temperatures should remain within
values reached on Wednesday.


As of 230 AM Tuesday: Friday, NHC forecast indicates that a tropical
cyclone will move across FL, moving over the Atlantic near
Jacksonville, FL during the morning. A sfc cold front over the
foothills and Piedmont may become briefly stationary Friday morning,
then start to slide east as the center of the tropical low moves
further off shore. The environment across the CWA should steadily
dry through the rest of the day. By the late afternoon, the leading
edge of a Canadian air mass should spread over the forecast area.
High temperature will likely remain limited to the upper 70s within
the mtn valleys to the mid 80s across the Lakelands.

This weekend through Monday, medium range guidance shows Canadian
high pressure will remain ridged across the western Carolinas and NE
GA. At the mid levels, the center of a 595 DM ridge should close off
near the MS/AL/TN connection. This pattern should result in slightly
below normal temperatures on Saturday, then gradually warming to
around normal by Monday. I will forecast dry conditions from Sat-Mon.


At KCLT...VFR through the period. Not much going on near the surface
tonight and into Wednesday, so wind should remain fairly light...out
fo the NE through this evening, then going light SE overnight, and
NE again Wednesday morning. A few high based stratocu this afternoon
will dissipate with sunset. With a bit of heating after sunrise on
Wednesday, we should develop few/sct stratocu with a base around 035
to 040 similar to the past few days.

Elsewhere: the only concerns will be low stratus/fog in the mtn
valleys again early Wednesday morning. Have included an MVFR
restriction at KAVL beginning around 08Z with a TEMPO for IFR
conditions around daybreak, as has happened the last couple of
mornings. Otherwise, similar to KCLT.

Outlook: Scattered high terrain convection may return Wednesday
afternoon, while convective chances increase in all areas as a cold
front pushes through on Thu. AM mountain valley fog/low stratus will
remain possible through the week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     Med   74%     High  94%
KHKY       High 100%     High 100%     Med   77%     High  94%
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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