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fxus61 krnk 231703 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
1203 PM EST Monday Nov 23 2009 


Synopsis... 
low pressure along the Carolina coast will track northeast and 
offshore tonight into Tuesday. Meanwhile...high pressure will 
build back into the area later Tuesday followed by a storm system 
arriving around Thanksgiving. 
&& 


Near term /through tonight/... 
another damp and dreary afternoon in store as most of the ongoing 
-ra slowly tapers to drizzle across the region with cold air 
damming in place. 12z radiosonde observations depict this well with deep relative humidity to 
nearly 6h and a good veering profile above the inversion layer. 
This should keep at least some -dz going with any drying aloft 
behind the init short wave getting tempered by trapped low level moisture 
under the inversion. Latest RUC/WRF even show some redevelopment 
of -ra over the north/west in advance of the short wave currently over 
the middle miss valley per vapor loop...so wont be too fast to lower 
probability of precipitation despite the gradual exodus of most -ra acros the east at this time. 
Otherwise keeping Cat/likely probability of precipitation east until middle/late afternoon for at 
least patchy -ra/areas -dz and tapering to lower chance as you 
move west of the Blue Ridge for the most part. Given wedge and NE 
flow under clouds expect only a few degrees of temperature rise mainly SW 
tier where some thinning/breaks possible later on. 


The drizzle will persist into the overnight...especially over the 
Blue Ridge and points east. The next shortwave entering the middle 
Mississippi Valley may enhance some lift over southeast WV this evening 
so there could be some rain lingering there. 


Tonight...clouds linger...so lows will be similar and even a 
couple degrees warmer than this mornings. 


&& 


Short term /Tuesday through Thursday night/... 
as a coastal low moves into New England...high pressure will wedge 
back south into the middle Atlantic. With no mechanism to mix out 
low level moisture...clouds will hang tough with drizzle and light rain 
Tuesday night. Based upon wind direction...northwest NC and extreme SW Virginia 
are the favored locations for more widespread drizzle or 
measurable light rain...however low level moisture remains sufficient 
for the slight chance of light rain across the entire County Warning Area. More 
southerly component develops Wednesday...but again clouds 
remaining in place should keep temperatures similar Tuesday/Wednesday in the 50s. 
With low pressure moving into the Great Lakes...a cold front will 
cross Wednesday and Wednesday night...allowing showers to break 
out. Both European model (ecmwf)/GFS are bullish on a closed 500 mb low moving into the 
Ohio Valley...allowing 850 mb -5c temperatures to enter the region by Friday 
morning. Downsloping wind does develop behind the front...so 
limited the highest probability of precipitation to the upslope region of southeast West Virginia 
Thursday/Thursday night. Snow/rain showers may not be able to penetrate 
into the New River valley until the upper low moves to the 
Mason/Dixon line on Friday...if it arrives as deep and cold as 
models suggest. 


&& 


Long term /Friday through Sunday/... 
measurable snow will be possible in the preferred upslope snow 
regions of southeast West Virginia into Friday...coverage of 
precipitation will be about the same...but with warming 
temperatures the precipitation should transition back to scattered 
showers...with a trend towards decreasing coverage late. 


On Friday night...even colder temperatures are expected with 
similar...or even slightly stronger wind gusts...but precipitation 
coverage will be less. Isolated snow showers will be 
possible...primarily over southeast West Virginia...neighboring 
parts of southwest Virginia...and in the mountains of northwest 
North Carolina. 


On Saturday into Saturday night...the pressure gradient will begin 
to weaken so look for slower wind speeds and gusts as compared to 
Thursday night through Friday night. Also...even less moisture will 
result in only isolated rain/snow showers in the mountains. 


By Saturday night...we are expecting a dry forecast with the coldest 
night of the weekend. Middle to upper 20s will be common in the 
mountains...with most areas east of the Blue Ridge around 30 or in 
the lower 30s. 


On Sunday...winds take on a bit more of a southwest component ahead 
of our next approaching cold front. There is a slight chance of some 
showers in the southeast West Virginia mountains in association with 
this approaching front on Sunday. 


&& 


Aviation /18z Monday through Saturday/... 
rain will continue to taper off to drizzle this afternoon...with 
at least patchy -dz continuing at times espcly along/east of the 
Blue Ridge through the overnight. Any improvement in the 
widespread IFR/MVFR conditions into early this evening will be 
short lived with IFR/LIFR ceilings expected to fill back in at most 
taf sites into Tuesday morning. Overall visibilities to also bounce 
around between IFR/MVFR in fog/-ra/-dz through much of 
tonight...with more in the way of dense fog at klwb after 
midnight. Kblf may tend to improve some later tonight as moisture 
continues to shallow out but not confident enough to show higher 
ceilings at this time. 


Low level moisture will be slowly diminishing from west to east 
Tuesday but just how far east any clearing gets a bit iffy. 
Appears a scenario where the far west including kblf/klwb see 
things go VFR but likely not until the end of the taf period and 
beyond. Elsewhere expect IFR/MVFR conditions to persist through at least 
midday with a gradual improvement into the afternoon. 


Low clouds likely to fill back in at least east of the Blue Ridge 
Tuesday night before the next approaching short wave from the west 
allows surface winds to veer around into the southwest on Wednesday. 
This should allow erosion of the leftover low level moisture and 
low clouds. 


Should see improvement of flight conditions back into VFR by 
Wednesday afternoon...but arrival of strong cold front Thursday 
into Friday will likely bring a return to MVFR conditions in 
upslope areas west of the Blue Ridge...along with an increasing 
threat of some mountain rain or snow showers. Downsloping 
conditions east of the Blue Ridge should help to keep those areas 
mainly in VFR range during the late week period. Appears strong 
upslope flow will keep this scenario persisting Friday night into 
at least early Sat with MVFR/IFR across southeast wva and mainly VFR in 
downslope flow out east. 


&& 


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


&& 


$$ 
Synopsis...jh/wert/wp 
near term...jh/wp 
short term...km 
long term...ds 
aviation...jh/wp 

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