Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 021821

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
221 PM EDT Tue Jun 2 2020

Increasing moisture and warmer temperatures will return to the
region from the west by Wednesday. Shower and thunderstorm chances
will increase Thursday and Friday ahead of an approaching cold
front, with the front likely crossing the region on Saturday. The
front may stall near the southern part of the area for the latter
half of the weekend into early next week, keeping isolated to
scattered showers and thunderstorms in the forecast.


As of 220 PM EDT...Upper ridge over the Southeast will begin to
break down, while sfc high pressure shifts east. This keeps a light
return flow over the area, and mid-lvl subsidence still keeping
things capped the rest of the aftn. Overall, it should be a quiet
night, with patchy fog in the mountain valleys of western NC. Min
temps will be a category or so above normal.

On Wednesday, as the mid-lvl ridging weakens, there will be less
capping for deep convection across the NC mountains. Guidance is
still mixed, with the NAM having almost no convective response in
our area. But most of the other guidance shows at least isolated
showers. Will keep slgt chc to low-end chc for mountain-top
convection. Not expecting anything severe with this activity. The
rest of the forecast area will remain dry and hot. First 90-deg day
possibly for the GSP site. Highs about 5-8 deg above normal.


As of 200 pm EDT Tuesday: A weakness in the subtropical ridge will
develop near the southern Appalachians by Thursday, and then remain
fairly persistent through Friday, providing enough forcing for above
climatology PoPs. As southwesterly flow gets better established
through the day on Thursday, moisture will return with mountain
ridgetop triggering developing quickly Thursday afternoon where
sbCAPE values run 2000 J/kg or higher. Likely PoPs for the afternoon
and early evening will be featured over the mountains. Triggering
will be weaker in Piedmont sections and slightly better capping will
need to be overcome to get coverage going. Will cap PoPs generally
in the solid chance range across the foothills and lower chance over
the Piedmont through late day. Expect plenty of upper 80s max temps
east of the mountains.

Moisture should be a touch deeper on Friday afternoon with continued
southwest flow. Triggering still looks focused mainly on the
mountains, but with slightly better coverage across the Piedmont
than observed on Thursday. The increased clouds may limit
instability a bit, but higher dewpoints should yield late day sbCAPE
near Thursday values. The clouds could shave a degree off Friday max
temps compared to Thursday.


As of 210 pm EDT Tuesday: Yet another shortwave in the NW flow aloft
on Saturday will dive into the weakness near the Appalachians
between the ridges of high pressure. This upper forcing will be
accompanied by a weak cold front, which should steadily progress
southeast across the region during the daytime Saturday. The
boundary and associated moisture will likely stall across the
southern half of the area for the latter half of the weekend,
keeping scattered shower and thunderstorm chances going for
especially the southern tier Sunday.

The eventual track of Cristobal will be the main feature to watch in
the extended period and beyond. It is likely that the system will
near the Gulf Coast by Saturday, but with a blocking ridge building
over the mid-MS River valley and into the southern Appalachians
through the weekend. This should slow the system, and perhaps shunt
it farther west over LA or TX on Sunday. Strong eastern ridging
should then give the tropical system a lane to pass northward west
of the MS River Valley before it gets picked up by the next strong
northern tier system early next week. Well east of the tropical
moisture, we should see mainly diurnal, scattered convection with a
mountain focus. Depending on the Cristobal track, there could even
be some suppressive subsidence at times. Expect near climo temps
through the period.


At KCLT and elsewhere: VFR conditions expected thru the 18z TAF
period, as dry high pressure persists. SW winds of 8-12 kts, with
some low-end gusts 15-20 kts, expected for the rest of the aftn.
then winds should become light overnight. Winds will be similar
tomorrow. A VFR-lvl cu field will dissipate after sunset, then
redevelop again by midday tomorrow. There will likely be some valley
fog, but confidence is too low on any fog in the French Broad
Valley, so the 18z AVL TAF will be VFR. A few showers and garden-
variety tstms will be possible in the NC mountains tomorrow aftn.
KAVL may need a mention of TS after 18z with later TAFs.

Outlook: Increasing heat and humidity will likely result in a return
of afternoon/evening convection by the end of the week. Otherwise,
VFR conditions each day, and mountain valley fog possible each

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%     High 100%     High 100%
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 are available at
the following link:




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