661 
FXUS62 KGSP 210009
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
809 PM EDT Mon Aug 20 2018

.SYNOPSIS...
A warm and humid air mass will remain in place across the region
tonight as a cold front approaches from the west. The cold front is 
forecast to move across the region on Tuesday afternoon and evening 
with scattered to numerous thunderstorms expected. In the front's 
wake, drier high pressure will spread over the area for the latter 
half of the week.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 5pm EDT Monday:  Blended in CAM data to reduce POP in 
the southwest quadrant of the CWA as CAM guidance and 
radar/satellite trends have much less coverage in that area this 
evening. Showers with some thunderstorms will continue until 
after dark with further initiation expected over the mountains 
and some southeast movement into the foothills and piedmont 
areas.

Patchy areas of fog will be possible towards daybreak. With high 
temperatures ranging from the low to mid 80s this afternoon, expect 
temperatures tonight to drop into the low 70s, cooler across the 
mountains. 

Back to the west, a closed upper low pushing eastward from the 
Plains will gradually open up as it moves into the OH Valley 
overnight, as it's north to south oriented associated cold front 
slowly pushes through the MS Valley. Per latest guidance, anticipate 
the front to near the western portion of the FA towards the end of 
the near term forecast period. Thus, with the front to the west, 
persistent SW flow, and upper support from a few passing waves of 
energy, expect another round of scattered to numerous showers and 
thunderstorms on Tuesday. While more impressive shear values along 
with other severe weather parameters will remain well to the north, 
will note the potential for isolated severe thunderstorms, as noted 
in the Marginal Risk from the SPC Day 2 Convective Outlook. Primary 
threat will be damaging winds. High temperatures on Tuesday will be 
around, if not just a few degrees above, normal.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 205 PM EDT Monday: A sharp upper trough axis moves east of the 
area to be replaced by a more broad and weaker trough for Wednesday 
and Thursday. At the surface, a cold front moves east of the area 
Wednesday, but a weak lee trough remains over the area. Low level 
flow turns northwesterly behind the departing front with deep 
moisture moving east as well. There will be some lingering low level 
moisture, so scattered diurnal convection may develop across the 
mountains, with isolated convection possible near the lee trough. 
High pressure builds in from the northwest for Thursday. This turns 
the low level flow more northerly or northeasterly. The atmosphere 
looks to be too stable for any diurnal convection to develop. Highs 
will be near normal Wednesday then fall to nearly 5 degrees below 
normal on Thursday as the cooler air mass associated with the 
building high pressure moves in. Lows follow a similar pattern.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 200 PM EDT Monday: Surface high pressure will build down into 
the forecast area on Friday leading to a cooler than normal day. 
Dewpoints are expected in the 50s to lower 60s which will feel very 
comfortable for this time of year. The high will slowly move off the 
coast over the weekend with a gradual modification to more normal 
conditions. Mid level ridging is expected to develop for the early 
part of next week with hot and muggy conditions returning. Some 
scattered storms are expected early next week primarily in the 
mountains.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Showers and some thunder will linger for a couple more hours this 
evening, primarily over the mountains, with very sparse activity 
after 02Z.  Areas which saw significant rainfall today will be the 
ones most like to see restrictions due to fog Tuesday morning, 
particular the KAVL, KGSP, and KGMU aerodromes. 

On Tuesday, a major front will approach the region from the 
northwest, with the frontal position reaching KAVL by 0Z Tuesday 
evening.  Winds will remain southwesterly ahead of the front at 5 to 
15 kts, and will veer more northerly after 00Z when the front 
passes. Front will help to focus showers and thunderstorms on 
Tuesday, with significant activity expected along and ahead of the 
front.  Timing in TAFs for VCTS and PROB30 TS reflect expected 
progress of the front, with storms once again beginning over the 
mountains and spreading southeastward.

Outlook: Expect good coverage of diurnal showers and thunderstorms 
thru early Wednesday. After which, drier high pressure is expected 
to build in behind a passing cold front. Until then, restrictions 
are likely mainly during the morning as low clouds form, and then 
under any afternoon and evening showers and thunderstorms.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z 
KCLT       High 100%     High  82%     High  82%     High 100%     
KGSP       High  91%     Low   55%     Med   73%     High 100%     
KAVL       Low   57%     Low   37%     Med   71%     High 100%     
KHKY       Med   71%     Low   36%     Med   66%     High  94%     
KGMU       High  88%     Low   58%     Med   71%     High  82%     
KAND       High  92%     Low   55%     Med   74%     Med   67%     

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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...SW
NEAR TERM...SGL/WJM
SHORT TERM...RWH
LONG TERM...SW
AVIATION...WJM