263 
fxus61 krnk 220356 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
1056 PM EST Friday Nov 21 2008 


Synopsis... 
a large high over the middle Mississippi Valley will build into the 
area tonight into Sunday. Another cold front will move through 
Monday. 


&& 


Near term /until 6 am Saturday morning/... 
have lowered min temperatures a few more degrees in most areas based on current 
temperatures/dewpoints and expectation of winds slowly weakening. As a result 
we have a few isolated high spots with wind chills (or so called 
apparent temps) dropping to advisory levels of -5f. These will 
likely be confined to elevations above 3500 feet so will mention in 
the severe weather potential statement with no headline. 


&& 


Short term /6 am Saturday morning through Monday night/... 
high pressure at the surface will gradually build from the 
west...helping to relax the pressure gradient across the area. 
With 850mb winds still at 30+ kts for the first part of the 
day...breezy conditions are still expected. 


As for temperatures...an upper level shortwave across the western 
Dakotas this afternoon will move southeast into the Missouri Valley 
by Saturday evening. As this wave approaches...mid/high clouds will 
increase during the day. This increase in cloud cover along with the 
absence of warm air advection should keep highs Saturday below 
guidance...and brought temperatures down a couple of degrees. 


The aforementioned shortwave zips through southwest Virginia into 
central NC by 12z Sunday. Low levels of the atmosphere remain very 
dry...so no precipitation is anticipated with this feature...but middle and 
high level clouds will keep temperatures warmer than usual in this 
airmass. Went a degree or so above guidance for lows...but temperatures may 
make a quick drop right before dawn Sunday...as shortwave moves east 
of the area between 09-12z. 


For Sunday...leaned toward warmer GFS MOS numbers for highs with 
sunshine...west flow and warming 850mb temperatures. 


Next system of concern approaches from the west...with frontal 
passage anticipated late Monday. GFS is slightly faster than European model (ecmwf) 
and with ensembles leaning toward the ecmwf's slower solution. 
Timing of the arrival of precipitation will be key for precipitation type. 
If faster GFS verifies...BUFKIT soundings suggest precipitation may begin 
as snow or freezing rain...but strong southwest flow ahead of the 
front should warm temperatures quickly enough for a fast transition to rain. 


After frontal passage Monday night...temperatures drop and upslope snow 
machine begins again. 


&& 


Long term /Tuesday through Friday/... 
an occluded low will hover over the northeast USA Tuesday through 
Thursday then slides off the coast on Friday. A series of short 
waves will bring reinforcing shots of cold air into the region 
through Wednesday. With wrap-a-round moisture from the upper level 
low and a short wave digging into the Carolinas Tuesday and Tuesday 
night...expect snow showers across the mountains with possible spill 
over into the foothills. Wednesday into Thursday...northwest flow 
with trajectories from the Great Lakes will continue snow showers on 
western slopes with scattered flurries/snow bands to the Blue Ridge. 
High pressure will build into the region shutting down the snow on 
Friday. 


Besides the snow and below normal temperatures...winds will be 
increasing through the period. Inversion and cloud cover should keep 
stronger winds aloft Tuesday and Tuesday night. Skies to become 
mostly clear outside of western slopes Wednesday afternoon and with 
momentum Transfer increasing and maintaining through Thursday...windy 
and gusty conditions are expected. Models not displaying any 
significant pressure rises...therefore will keep winds below 
advisory criteria. 


&& 


Aviation /04z Saturday through Wednesday/... 
VFR through the next 48 hours with winds becoming light by late 
Saturday. 


Winds have weakened considerably across the area late 
this evening...however turbulence still an issue as pressure gradient 
remains tight coupled with 40 knots low level jet. Cross barrier 
winds above 3000 feet will run about 20 to 30 knots through midday 
Saturday. High pressure should be centered over the area by Saturday 
afternoon. 


A short wave will cross over the area Saturday night...spreading 
thick middle and high level clouds into the region during the afternoon 
Saturday. 


Another cold front arrives Monday with chance of rain and snow 
showers. 


&& 


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


&& 


$$ 
Synopsis...jh/kk 
near term...ams/js 
short term...ph 
long term...rcs 
aviation...js/rcs