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fxus61 krnk 200642 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
242 am EDT Wednesday Aug 20 2008 


Synopsis... 
a weak cold front will drift south through the region today before 
dissipating over North Carolina tonight. High pressure behind the 
front will ridge south across the area Thursday through much of 
the weekend. Another weak cold front may slide southeast into the 
Appalachians by early next week. 


&& 


Near term /through tonight/... 
weak back door front continues to sag south into the region this 
morning with areas of ac/SC along the boundary across the north. 
Expect some of this cloudiness to linger espcly eastern slopes early 
this morning before dry easterly flow mixes things out this 
afternoon. Added column drying prevails this afternoon with only 
sheared cirrus and perhaps some cumulus despite mixing/weak instability. 
Leaned a bit more toward the warmer mav MOS highs per a warm start 
and more afternoon sun. 


Surface high takes on more of a wedge config along/east of the 
ridges overnight with more low level east/NE flow developing late. 
Nearly all model guidance pointing to enough relative humidity to support a period 
of low clouds along the Blue Ridge by morning with even some 
spotty -shra. Since that appears a bit overdone given shallow relative humidity 
and little support aloft wont include any probability of precipitation at this time but intro more 
clouds after midnight espcly central zones. Like slightly warmer 
met MOS lows tonight given possible low clouds late and a little 
more mixing. 
&& 


Short term /Thursday through Friday night/... 
an upper level ridge of high pressure builds over the region Thursday 
and perists through Friday night keeping overall dry conditions in 
place. However the associated surface high will be gradually 
sliding off the middle Atlantic coast with the flow becoming more southeast 
with time. Appears subsidence quite strong on Thursday with part of the 
surface high nearby so persistence mainly sunny/warm forecast on 
track after early clouds mix out. Guidance suggests that arm of 
deeper moisture will be working inland Friday as Fay pivots back 
to the west. This arc of rain showers may make a run across the south by 
afternoon per the latest GFS. Although this iffy given dry air in 
place aloft...appears low level upslope flow combo with increasing 
precipitable waters  could prompt a rain showers or two espcly northwest NC so adding 20 probability of precipitation 
south for now. Otherwise expect more clouds with deeper onshore flow 
Friday into Friday night with temperatures a little cooler Friday under 
a weak wedge scenario. 


&& 


Long term /Saturday through Tuesday/... 
as compared to this time yesterday...the influence of Fay on our 
weather for the weekend is looking a lot less. The latest official 
track of indicates a slower system that will turn west towards 
southern Alabama...rather than track north into North Carolina. 
So...have backed down considerably on precipitation chances and 
increasing cloud cover trends through Sunday. 


Past Sunday...if Fay tracks as planned...we may start to see some of 
its associated moisture get drawn out of the lower Tennessee Valley 
into the base of a northern stream trough that will be heading 
southeast into New England and the Middle-Atlantic States. Will be 
carrying scattered showers and storms Monday into Tuesday to account 
for this potential...but confidence is low given where Fays 
associated moisture will end up. Without Fay...the northern stream 
trough will be encountering the relatively drier air of the departing 
upper ridge...and precipitation with it would be limited. 


&& 


Aviation /06z Wednesday through Sunday/... 
backdoor front will move through the area during the period. With 
a dry atmosphere in place...front could move through the area 
virtually dry with only an increase in VFR clouds through the 
morning. Mixing during the day will help scour cloud deck in the 
afternoon. Easterly flow to bring in moisture under an inversion 
Wednesday night. This may bring MVFR clouds along and east of the 
Blue Ridge after 06z Thursday. 


Dry high and easterly flow will keep a persistent weather pattern 
over the region. VFR conditions expected during the day with some 
MVFR conditions possible along and east of the Blue Ridge at night 
through the weekend. 


This weekends forecast may linger into early next 
week...however...Fay will have the final say so. 


&& 


Rnk watches/warnings/advisories... 
Virginia...none. 
NC...none. 
WV...none. 


&& 


$$ 
Synopsis...jh 
near term...jh 
short term...ds/jh 
long term...ds 
aviation...rcs