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FXUS62 KGSP 170742

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
342 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 315 am: 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, with scattered to numerous showers underway 
across southern Middle TN. This activity will progress toward the 
southern Appalachians, with at least isolated activity likely across 
southwest NC by mid-morning. Pops will therefore ramp up across 
western areas through the morning, reaching likely across all of the 
NC mtns by mid-afternoon, as the better UVV interacts with an 
unstable air mass. 

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. 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: Low stratus is possible at KAVL this morning, 
with the site recently having picked up FEW002. This is handled in 
the TAF with a tempo for 3SM/BKN003 from 09-12Z. Otherwise, VFR 
conditions are forecast to persist at the terminals through the 
period. An upper air disturbance (which happens to be all that's 
left of former Tropical Storm Barry) will pass over the area this 
afternoon into the evening. This will enhance shower and 
thunderstorm chances over the mtns, and a VCTS/Prob30 is included at 
KAVL throughout the afternoon into early evening. Due to questions 
above 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 

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...

            07-13Z        13-19Z        19-01Z        01-06Z 
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  96%     
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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