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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
236 am EDT Wednesday Aug 20 2008 


Synopsis... 
high pressure will remain centered near New England for the next few 
days...while tropical cyclone Fay will stall over the NE coast of 
Florida...then move back to the west along the northern Golf coast 
over the weekend. It remains unclear if Fay will affect our weather 
early next week. 


&& 


Near term /through today/... 
another quiet day on tap...as upper heights build over the middle 
Atlantic...while Fay stalls in vicinity of the Florida Atlantic coast. A weak 
backdoor cold front pushes into the area this morning...then washes out 
by midday. The NAM tries to create a little instability along the 
boundary...with some showers/thunderstorms developing. Strong subsidence should 
maintain a capping inversion around 650 mb. So I keep the forecast dry 
(just expecting a few cumulus with cirrus ovrhead). Strengthening Ely low level 
flow will result in downsloping in the French Broad and other mountain 
valleys. So I went above MOS for temperatures in the valleys by a couple degree. 
Elsewhere...MOS consensus looks good...with maximum temperatures in the upper 80s north to 
lower 90s S (east of the mtns). 


Tonight...moisture under the inversion increases...with an upslope 
component to the flow along the Blue Ridge Escarpment. I increase cloud 
cover there...but keep the probability of precipitation dry...given no real support for 
convection. Min temperatures should be close to normal (50s to lower 60s mountains 
and middle to upper 60s piedmont). 


&& 


Short term /tonight through Saturday night/... 
as of 210 am Wednesday...the latest TPC track continues to take 
Fay farther and farther to the south as it boomerangs back to the 
west Thursday through Sat. What this means is our weather will be 
predominately controlled by a deep layer ridge of high pressure 
which is what will steer the tropical cyclone back to the west. 


For Thursday...dewpoints should mix into the u50s to l60s once 
again. They will probably be even lower than that in the mountains. 
The GFS mixed dewpoint tool implies that they could fall to around 
50 in the interior SW NC mountains...though I won't go that low on 
account of collaboration issues. With a strong subsidence inversion 
persisting across the forecast area...I/ll maintain the completely dry forecast 
for Thursday. 


Friday shows about the best increase in low level and layer relative humidity/S of any of 
the next several days. Clouds...both middle and high level...should be 
on the increase. However...the middle level ridge will remain strong 
and while there may finally be some upslope induced shower or thunderstorm 
activity...it won't be very widespread. Of course...if Fay were to 
move farther north once it moves inland...then this scenario would 
be quite different. The Canadian global model for example has quite 
a bit of precipitation over the western Carolinas and NE Georgia as it takes the 
remnants farther north. Alas...this model is an outlier...and dry 
will probably be the order of the day. On Saturday the 
ridge...both at the surface and aloft...will actually strengthen a 
little... resulting in more drying. This will probably suppress 
any convection...but I held on to the day shifts pop orientation 
and values - slight chance for the most part - as this seemed 
reasonable. 


&& 


Long term /Sunday through Tuesday/... 
as of 215 am Wednesday...I hate to sound like a broken record...but 
the extended forecast will be driven by the track of Fay and it/S 
remnant moisture. Heights fall over the NE and Middle-Atlantic States 
on Sunday...but the ridge over the southeast states is looking stronger on 
the latest GFS. In fact...the GFS stalls Fay over the northern gom 
and is very reluctant to take it northward into the ridge Sunday and 
Monday. The old ec was weaker with the ridge and allows Fay to start 
lifting north...though it wouldn/T be until around Tuesday that it 
reaches US. 


The previous extended had chance probability of precipitation over the southern half of the forecast area on 
Sunday and over the entire forecast area on Monday and Tuesday. I see nothing 
in the latest model runs to cause ME to want to deviate from this 
solution. I just hope the GFS is not a perfect forecast as that would be 
very bad news for the Gulf states and for the our region where we 
really need the rain. 


&& 


Aviation /07z Wednesday through Sunday/... 
VFR conditions for the next 24 hours...save for visibility restrictions at 
kavl and khky in hz/br. Middle level clouds continue over the central mountains 
and upper Savannah River valley. Elsewhere...a decent amount of cirrus continues to 
stream in from the west. Dewpt depressions are greater than last 
couple of nights...so I did not feel comfortable going any lower on 
visibilities. Later today...few to scattered deck of cumulus with bases around 7-8 kft is 
expected under a scattered to broken cirrus deck. Winds will increase out of the east 
this afternoon...as Fay moves a little closer to our area. Hi pressure aloft 
should keep the area free of rain showers/thunderstorms and rain activity. 


Outlook...high pressure will persist through at least late-week as 
Tropical Storm Fay wanders around near the Gulf Coast. It now 
appears that any effects that this system has on the weather across 
the western Carolinas are at least a week away. However...isolated 
to widely scattered afternoon/evening showers and thunderstorms will 
be possible over the weekend. 


&& 


Gsp watches/warnings/advisories... 
Georgia...none. 
NC...none. 
SC...none. 


&& 


$$ 
Synopsis...McAvoy 
near term...Arkansas 
short term...McAvoy 
long term...McAvoy 
aviation...Arkansas