Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 270720

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
320 AM EDT Thu Jun 27 2019

Typical summertime afternoon and evening thunderstorms will likely
return today through much of the weekend under a shallow ridge of
high pressure over the southeast. A cold front arriving from the
north very late in the weekend will likely dissipate over the
southeast by Sunday night. Hot and humid high pressure will set up
Monday through Wednesday.


As of 305 AM EDT Thursday: High clouds have largely thinned out
across the region, which has supported some isolated fog development
for southwest mountain valleys. This should continue to fill in to
these areas with an outside chance of seeing brief patchy fog across
other mountain valleys.

Increasing moisture across the region today due to a weak
disturbance to our west combined with steep lapse rates is expected
to support diurnally driven isolated to widely scattered showers and
thunderstorms across the mountains with some very isolated activity
also possible east of the mountains, especially along and south of
the I-40 corridor. SPC has us in general thunder which seems
appropriate given a relative lack of moisture and a forcing
mechanism. However, can`t rule out a couple of stronger pulse type
thunderstorms across the mountains given weak shear, moderate
instability, and steep lapse rates with damaging wind being the main
threat. Without significant forcing in place, convection will
quickly weaken around sunset. Outside of scattered cu forming due to
afternoon heating, some high clouds will continue to stream
overhead, limiting highs to the mid 80s mountain valleys to near 90
east of the mountains. High clouds are expected to linger overnight
limiting lows to the mid 60s to near 70.


As of 310 am EDT Thursday: A closed upper low or trough over the
Mississippi Valley on Friday will continue to retrograde westward,
with upper heights and surface high pressure building over the
southeast U.S. Southeasterly low-level flow off the Atlantic should
allow boundary layer moisture to steadily recover and permit an
uptick in diurnal PoPs. The southeast ridge will then persist on
Saturday as a rex blocking pattern develops from the desert
southwest to the midwest, while heights fall from Quebec to New
England. Anticipate mainly scattered diurnal convection to continue,
especially over the mountains. Maximum temperatures will climb from
one category above climo Friday to around two categories above climo
on Saturday afternoon.


As of 315 am EDT Thursday: The ongoing rex block ridge will extend
across the Ohio Valley and into the Appalachians on Sunday, as a 500
mb low pressure system moves offshore from New England. Isolated to
scattered mountain convection will continue across the southeast
through the afternoon and evening, and a more prominent lee trough
could contribute to isolated piedmont activity as well late in the
day. It now seems more likely that any surface cold front running
southward from the mid-Atlantic late in the weekend will dissipate
as it reaches the northern fringes of the forecast area Sunday night
into Monday morning.

A reasonably strong ridge will continue over the southeast Monday
through Wednesday, with hot temperatures developing. It is possible
that weak vorticity lobes topping the ridge could batter it down
slightly from time to time, with northern tier convection becoming a
bit more likely each day, but that is highly uncertain in the days 5
to 7 timeframe and PoPs will be confined to the chance category. The
heat and humidity seem much more certain, with plenty of near 100 or
better heat index values across the southeast half of the forecast
area, especially on Tuesday. Minimum temperatures in the lower 70s
in many areas will provide little respite from the heat. Currently,
it seems that only the extreme southern piedmont should flirt with
105 values, so will hold off on an HWO mention for another day.


At KCLT and elsewhere: VFR cigs/vsbys and light winds expected to
prevail through the period. There is a 30 percent chance of MVFR br
at KAVL between 09-12Z. There is also a 10 percent chance of showers
or thunderstorms sometime between 20Z and 03Z at KCLT and and KHKY,
with a 20 percent chance at other TAF sites. Sct to bkn low VFR cigs
are likely at all TAF sites during this time period.

Outlook: Isolated to scattered convection will be through the
weekend across the forecast area, with morning fog/stratus possible
each day as well, for mainly the mountain valleys.

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  86%     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 and ensemble forecasts
are available at the following link:




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