787 
fxus61 krnk 040545 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
145 am EDT Friday Jul 4 2008 


Synopsis... 
a cold front will slowly approach...and then stall across the 
eastern parts of the area as the Holiday weekend progresses. 
Precipitation chances will maximize on Saturday afternoon. Past 
the weekend...high pressure will briefly return to the area before 
another cold front approaches mid-week. 


&& 


Near term /through today/... 
baroclinic zone and surface front extend from middle Mississippi Valley 
northeast across the Ohio Valley. The front and better lift from 
short waves and upper jet streaks drift southeast tonight and 
Friday. Current radar trends indicate showers moving through West 
Virginia will likely push into far northwest portions of the 
County Warning Area...so have updated to add chance probability of precipitation to that area. Activity 
likely to diminish as it moves east into much drier air so did not 
carry probability of precipitation much beyond the western slopes. 


Expect middle and high clouds to spill into the northern County 
Warning Area overnight. This cloud cover should keep temperatures up 
enough to limit any valley fog. Models keep low levels dry and 
surface dew points in the 50s...especially in the southwest part of 
the forecast area until Friday. Low level moisture and dew points 
increase on Friday. A weak Lee trough will develop by afternoon. Have 
increased chance of rain with likely probability in the 
northwest...tapering off to slight chance in the southeast. 


Have lowered minimum temperatures in the New River valley and far 
southwest counties since surface dew points will still be in the 50s 
tonight and there will be some rapid radiational cooling in the 
evening before any high clouds come in...if they are even opaque 
enough to block radiational cooling that far south. Guidance has 
also been too warm for bcb past few night. 


&& 


Short term /tonight through Sunday/... 
the cold front will advance closer to the area with a good fetch of 
moisture advecting into the area in advance of it. While the loss of 
sunshine Friday evening may briefly reduce coverage of the 
convection...a shortwave trough rotating through the Ohio Valley 
after midnight should allow for increased development..especially in 
the west...by Saturday morning. During the day Saturday the front 
will slowly inch its way into the eastern part of the area. Have 
bumped the chance of precipitation up in most areas by 5 to 10 
percent above the previous forecast to reflect greater confidence. 
Slowly Saturday night into Sunday...the front itself will wash out 
to a poorly defined low pressure trough. This trough is prognosticated to 
make its way east of the forecast area by Sunday afternoon. Because 
of this we will see the focus for the best coverage of precipitation 
to also shift to the eastern parts of the area. Enhance cloud cover 
and precipitation will allow for a cooler day Saturday and Sunday as 
compared to Friday. 


&& 


Long term /Sunday night through Thursday/... 
for the most part...the area will stay in a weather pattern that 
will provide for periodic waves of energy rounding the base of a 
persistent trough across the Great Lakes...along with associated 
surface cold fronts approaching or making it into the region. The 
exception may be on Monday into Tuesday when the Bermuda high makes 
an attempt to retrograde towards the coast. But even with this...our 
low level moisture will remain on the high side...and typical 
summertime convection will allow for a continuation of isolated to 
scattered showers and storms on these days. Coverage of 
precipitation will increase by Wednesday with the approach...and 
then stalling of our next cold front. 


&& 


Aviation /06z Friday through Tuesday/... 
a few light showers are possible early this morning in the 
Greenbrier Valley. High clouds will hinder fog develop this morning. 


Moisture will continue to increase and scattered thunderstorms are 
expected this afternoon...mainly after 16z. The best chance for 
thunderstorms will be at blf and lwb with the chance tapering off 
further east and south. Some of the thunderstorms this afternoon and 
evening may contain damaging wind and large hail. 


Similar conditions are expected again Saturday and Sunday. The rain showers/thunderstorms and rain 
threat will continue into next week as frontal boundary stalls to 
our north. 


&& 


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


&& 


$$ 
Synopsis...ds 
near term...ams/js 
short term...ds 
long term...ds 
aviation...kk/km