947 
fxus61 krnk 240736 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
336 am EDT Thursday Jul 24 2008 


Synopsis... 
a weak surface high pressure system will build into the Middle Atlantic 
States from the west through Friday...bringing mild and dry 
weather for the next couple of days. This system is expected to 
drift offshore Friday into Saturday...allowing a series of weather 
disturbances to move back into the area over the weekend into 
early next week. 


&& 


Near term /through tonight/... 
surface high pressure will approach the area from the west 
today...and move overhead tonight...bringing slightly cooler 
temperatures and significantly lower dew points into the region 
through the period. Afternoon high temperatures today should range 
from the lower and middle 70s across the higher elevations...with 80s 
common elsewhere. 


Clear skies and light winds should support a good radiational 
cooling event tonight...with overnight low temperatures likely to 
fall into the 50s across most areas. Some patchy early morning fog 
may develop in some of the mountain and river valleys. Forecast 
guidance for high and low temperatures through the period is very 
similar and was generally accepted with little adjustments needed. 


&& 


Short term /Friday through Saturday/... 
surface ridge of high pressure is expected to drift offshore 
Friday afternoon into Friday night. Winds on backside of departing 
high will gradually veer around into the southeast...beginning a 
slow increase in dew points. Although subsidence inversion is 
expected to persist over most areas through the day...weak 
increasing upslope flow and differential heating may be sufficient 
to break cap and support an isolated to widely scattered shower or 
thunderstorm across the western mountains by middle-late afternoon. 


Threat of showers and thunderstorms will gradually increase on 
Saturday as first in another series of short wave troughs moves east 
through the area. Lead disturbance...currently over Colorado... 
expected to arrive in the area late Friday night into Saturday. 
Weak isentropic lift/forcing associated with this feature will 
support mainly diurnally driven scattered to widely scattered 
precipitation into the first part of the upcoming weekend. 


&& 


Long term /Saturday night through Wednesday/... 
mean broad upper trough over the northeastern portion of the nation 
is expected to amplify late in the weekend into early next week 
as a second and more significant wave...currently moving through 
northern Washington state...moves east across southern Canada and 
then dives southeast through the Great Lake region on backside of 
eastern upper trough. Approach of this wave and associated cool 
front will maintain threat of showers and thunderstorms over the 
middle Atlantic region on Sunday. There is the possibility that this 
front will then stall over/near the middle Atlantic region until a 
third wave transits the area Monday or Tuesday. With this in 
mind...will continue with threat of mainly diurnally driven 
thunderstorms through the period...or at least until passage of 
final wave can be better determined. 


With mean upper trough likely to persist over the middle Atlantic 
region throughout the middle and long term period...temperatures 
should remain close to seasonable normals. Temperature guidance 
appears reasonable and was generally accepted with little 
modification. 


&& 


Aviation /07z Thursday through Monday/... 
dew point front slow to move through the area overnight and with 
clearing skies and saturated ground...fog development is likely in 
mountain valleys and Piedmont sites. MVFR fog could be widespread 
across the area with IFR/LIFR conditions in mountain 
valleys...particularly lwb. VFR conditions are expected after 
sunrise with northwesterly wind...possibly as high as 10 knots. 


Series of short wave troughs are expected to pass east through the 
southern middle Atlantic region later Friday and into the 
weekend...each of which will reintroduce the threat of widely 
scattered showers or thunderstorms along with localized mainly MVFR 
restrictions to visibility and/or ceiling. 


Otherwise...expect to see general VFR conditions to prevail for most 
of the time at all terminal forecast sites from today through the 
upcoming weekend. 


&& 


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


&& 


$$ 
Synopsis...wert 
near term...wert 
short term...wert 
long term...wert 
aviation...rcs