FXUS62 KGSP 171455

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1055 AM EDT Wed Jul 17 2019

Summertime heat and humidity will continue into the upcoming
weekend. Moisture from the remnants of tropical cyclone Barry will
overspread the region from the west starting today, increasing the
coverage of daily showers and storms.


As of 10:45am EDT Wednesday: Area still on track for some
thunderstorms again this afternoon, more numerous in the mountains,
as usual. HRRR has somewhat better coverage of thunder in piedmont
areas, and blended some of that into the near-term POPs, giving at
least an outside chance for a storm at any location. At this point,
a few convective showers are already forming over parts of Northeast
Georgia, with a broad area of showers west of the Southern
Appalachians that is expected to make some eastward progress through
the afternoon.

Short wave ridging will de-amplify over the Southeast and Mid-
Atlantic today, as a short wave trough...representing the last gasp
of TC Barry...lifts from the TN Valley this morning into the central
Appalachians by this afternoon, dampening at it does so. Anomalously
strong low-to-mid level flow associated with this trough is
resulting in a region of moist warm advection across the TN Valley
this morning.

Increasing cloud cover across the mtns, along with deep mixing and
an increasing downslope flow affecting much of the Piedmont and
foothills juxtaposed beneath meager mid-level lapse rates will act
to limit instability across the area this afternoon, with CAPE
forecast to be limited to around 1500 J/kg. And despite the
respectable flow (for July anyway), unidirectional wind profiles
will limit shear parameters to the weak side of the spectrum. The
severe weather threat is therefore quite low. In fact, with the
better forcing lifting west of the Appalachians and the lacking
thermo profiles (not only a lack of robust instability, but some
degree of low level inhibition/high LFCs), convection is expected to
struggle making it out of the high terrain into the Piedmont and
foothills late this afternoon/evening, so pops drop off sharply to
20-30% south and east of the Blue Ridge. Max temps will be very
similar to yesterday, perhaps a degree-ish warmer across the
Piedmont, and a degree or two cooler in the increasing cloud regime
across the far western mountains.

What's left of the diurnal convection will shift east of the area
and/or dissipate by late evening. However, NW low-level flow (around
20 kts at H8) acting on lingering instability across the TN Valley
may allow isolated to scattered convection to initiate across the
southern Appalachians through the night, with the NAM being
particularly excited by this scenario. 20-40 pops are therefore
maintained along the TN border through the night.


As of 300 AM Wednesday: Thursday looks like it may be our "coolest"
day of the week, as increased cloud cover is expected associated
with the remnants of Barry. PWATs will be around 2-2.15". The cloud
cover may limit instability somewhat, and the latest guidance has
trended a little lower on PoPs. Still expect scattered to numerous
showers and tstms during the aftn and early evening. Highs will a
deg or two above normal, mainly mid 80s mountain valleys and lower
90s piedmont.

Friday...an expansive mid-level ridge will build in the wake of
Barry's remnants, resulting in temps back into the mid 90s along
with sticky dewpts. Despite the building ridge, scattered diurnal
convection is expected to develop thanks to strong insolation. PoPs
mainly in the chc range. Heat indices will climb into the 100-105
range across the entire piedmont.


As of 315 AM Wednesday: The broad mid-level ridge will be at its
strongest on Saturday, still centered over the central Appalachians
or Mid-Atlantic. A developing heat wave is expected along much of
the Eastern Seaboard, with the FA just on western edge of the heat
bubble. Highs Saturday still look to be in the mid 90s across the
Piedmont, with a few 96-97 readings possible along the I-77
corridor. Dewpts remaining in the lower to mid 70s should result in
heat indices around 100-105 again Saturday aftn. A few pixels of 105-
107 in spots around the Charlotte metro area. As with Friday,
scattered aftn convection can be expected across the FA, with
highest coverage in the mountains.

Sunday thru Tuesday...the heat wave is supposed to break, as a
trough digs into the Upper Midwest and breaks down the ridge over
the Northeast and Mid-Atlantic. Temps should trend down a tad toward
normal Sunday and Monday, and possibly slightly below normal
Tuesday, as the trough amplifies over the eastern CONUS. Heat indices
should return to more tolerable levels, and PoPs remain elevated
with height falls aloft combined with high theta-e in the low-
levels. A synoptic front will sag southeastward and settle over the
area on Tuesday. So Tuesday has the highest PoPs with likelies
across the entire FA.


At KCLT and elsewhere: The window for development of low stratus at
KAVL is closing quickly. There have been some instances of FEW002
showing up in the Metar there, and this may continue for another
hour or so, but no restrictions will be included in the forecast. In
fact, prevailing VFR conditions are forecast to persist at all
terminals through the period. An upper air disturbance (which
happens to be all that's left of former Tropical Storm Barry) will
pass near the area this afternoon into the evening. This will
enhance shower and thunderstorm chances over the mtns, and a
VCTS/Temp for TSRA is included at KAVL throughout the afternoon into
early evening. Due to questions about available instability, chances
for convection become substantially more iffy east of the mtns, but
evening Prob30s for TSRA are included at all sites except KAND. SW
winds winds will begin increasing late this morning, becoming 10-15
kts by early afternoon, when some gusts to around 20 kts will also
be possible. Winds will diminish to around 5 kts or less this
evening. Chances for morning stratus and/or fog will be a bit higher
Thursday, but available guidance offers nothing at all conclusive in
that regard, so a forecast of 6SM/BR at KAVL and KHKY is the only
thing out of the ordinary in the outlook period.

Outlook: Typical scattered diurnal convection is expected into the
weekend, especially over the mountains. Patchy mountain valley fog
and low cigs remain possible during the overnight and early morning

Confidence Table...

15-21Z 21-03Z 03-09Z 09-12Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL High 100% High 100% High 100% High 81%
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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