619 
fxus61 krnk 231515 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
1015 am EST Monday Nov 23 2009 


Synopsis... 
low pressure along the Carolina coast will track northeast and 
offshore later this afternoon into Tuesday. Meanwhile...high 
pressure will build back into the area 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 /15z Monday through Friday/... 
rain will continue through the day...especially from 
Roanoke...east to Dan/lyh. The rain should lighten by midday which 
will bring ceilings down below 1kft. Ceilings will start in the IFR to 
LIFR range at blf/lwb at the start or soon. The light rain/drizzle 
will linger into tonight but end over southeast WV overnight. Looking at 
IFR or less conditions to last through this taf period at all 
sites. Dense fog is expected at lwb after midnight. 


Little change is expected perhaps into Tuesday night before next 
approaching short wave from the west allows surface winds to veer 
around into the southwest...gradually eroding the low level 
moisture and low clouds. Many of the mountain ridges may have 
prolonged LIFR conditions. 


The west slopes of the Appalachians may be the only area to 
experience any MVFR condition the next couple of days. 


Should see overall improvement of flight conditions back into VFR 
by Wednesday...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. 


&& 


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...ams/wp