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Area Forecast Discussion

FXUS62 KGSP 301837

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
237 PM EDT TUE AUG 30 2016

A weak tropical system will gradually move back off the North Carolina
Coast tonight and tomorrow. A cold front will approach the region from
the north tomorrow night with another tropical system emerging from the
Gulf of Mexico on Thursday. This system is expected to remain just to
our south and then east as it moves offshore over the weekend. A Canadian
air mass will build over the region in the low`s wake.


As of 230 PM...a few showers have developed over the Lakelands, so a
small precip chance will have to be nudged up a bit there. Temps
look good still. We could yet develop a few showers near the TN
border over the Smokies owing to some slightly better instability.
Otherwise, the surface ridge over the area will continue to support
a relatively low theta-E air mass, which combined with poor
mid-level lapse rates will yield little in the way of buoyancy
across the rest of the area this afternoon.

The next 24 hours look relatively benign across the western
Carolinas in spite of a pronounced weakness aloft in the subtropical
ridge across the southeastern United States. The short range models
actually further develop a weak upper low along the southeast coast
tonight and early Wednesday, with a surface reflection slowly
deepening and moving along the GA/SC coast thru Wednesday afternoon.
However, this feature will remain just out of our reach and any
precip associated with it will not reach this far N and W. The mtns
should see some instability on Wednesday afternoon so a chance of
showers and thunderstorms looks good there. In between the mtns and
the coast...the air mass will be plagued by poor lapse rates and
limited instability...along with weak subsidence. This suggests
little chance for precip across the Piedmont zones. Temps will
remain a few degrees above normal thru the period.


As of 215 PM Tuesday...A vigorous positively tilted trough will dig
across the Great Lakes as it approaches the Northeast States during
the Short Term. A cold front associate with the trough will cross
the Ohio Valley late Wednesday, and push across the CWFA on
Thursday. The front will have limited moisture and forcing to work
with, but should provide a band of showers and TSTMS Thursday
afternoon through Thursday evening. A model blend features a solid
chance PoP across the area, highest along the TN border. Temps will
be a couple categories above normal, Thursday.

On Friday, cooler and drier air will push in behind the front, as
high pressure builds in across the Midwest to the Mid-Atlantic. The
main feature to watch will be Tropical Depression 9, which will
likely be a tropical storm by the Short Term. The latest NHC track
takes this system from the eastern Gulf to the NE across northern FL
and then parallel to the SC coast, but just offshore. This system
will likely interact with the front and upper trough and may rapidly
strengthen into a post-tropical or extra-tropical storm. The 12z GFS
keeps the system close to the coast, but still has minimal effects
for our area, as we remain on the NW side. I went with Superblend
for Friday, which results in a dry forecast and near normal temps.


As of 220 PM EDT Tuesday, the medium range fcst picks up at 00Z on
Saturday with an upper trof axis moving off the New England Coast
while steep upper ridging spreads across the Mississippi River Valley
in the trof`s wake. At the same time, the upper low associated with
TD9 will likely be somewhere along the southeast coast by the start
of the period. Large discrepancies still exist between the individual
models wrt the track of this system throughout the medium range with
the latest 12Z GFS and CMC keeping the system right along the Atlantic
Coast thru early next week while the 00Z ECMWF moves the low well
offshore on Saturday. Either way, the period will end with the upper
ridge axis moving east of the CWFA by early next week.

At the sfc, the tropical low now currently known as TD9 will likely
be located somewhere along the Carolina Coast or just offshore of the
coast by early Saturday. The ECMWF remains faster, moving the low off
the NC coast on Saturday, while the GFS keeps the system near the
coastline into early next week. The Canadian model remains the farthest
west and slowest wrt the storm track. Regardless, by late Sat/early Sun
the GFS and ECMWF agree that the low will be well to our northeast and
Canadian high pressure will spread back over the region and persist thru
day 7. As for the sensible fcst, I have a dry fcst with essentially all
of the deeper tropical moisture remaining to our south and east. Temps
will start out slightly below climatology and slowly warm thru the period.
By early next week they should be near climo again.


At KCLT...VFR through the period. Not much going on near the surface
tonight and into Wednesday, so wind should remain fairly light...out
fo the NE through this evening, then going light SE overnight, and
NE again Wednesday morning. A few high based stratocu this afternoon
will dissipate with sunset. With a bit of heating after sunrise on
Wednesday, we should develop few/sct stratocu with a base around 035
to 040 similar to the past few days.

Elsewhere: the only concerns will be low stratus/fog in the mtn
valleys again early Wednesday morning. Have included an MVFR
restriction at KAVL beginning around 08Z with a TEMPO for IFR
conditions around daybreak, as has happened the last couple of
mornings. Otherwise, similar to KCLT.

Outlook: Scattered high terrain convection may return Wednesday
afternoon, while convective chances increase in all areas as a cold
front pushes through on Thu. AM mountain valley fog/low stratus will
remain possible through the week.

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%     Med   74%     High  94%
KHKY       High 100%     High 100%     Med   77%     High  94%
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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