549 
fxus61 krnk 231114 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
614 am EST sun Nov 23 2008 


Synopsis... 
high pressure will slide slowly east of the area today and 
offshore overnight. A cold front will approach from the west 
Monday and pass through the region Monday evening. Cold northwest 
will follow the front later Monday night through Wednesday 
resulting in more mountain snow showers...as well as below normal 
temperatures into midweek. 


&& 


Near term /through tonight/... 
middle level wave seen on water vapor will slide southeast of the area this 
morning taking current swath of middle clouds out of the region 
around daybreak. Brief short wave ridging and good subsidence following 
this feature should result in mainly sunny skies today along with 
warming temperatures per developing 850 mb warm advection espcly this 
afternoon. Since mixing looks rather light given the surface ridge 
nearby wont go too much above MOS which has been warm of late. 
Thus going mainly 40s southeast wva over residual snow cover to 46-51 
elsewhere west...to the low/middle 50s east. 


Warm advection will increase overnight ahead of the next upstream 
short wave trough and associated cold front prognosticated along the miss river by 
morning. Expect some increase in high clouds west late but 
appears any low level relative humidity should stay just west so going without 
probability of precipitation overnight. Lows temperatures will be tricky with more mixing at 
elevation and better rad cooling east/valleys espcly early on 
under clear skies. Looks like a good 10-15 degree range possible 
between ridges/valleys so lowered temperatures below MOS western valleys 
and boosted at elevation across the SW. 


&& 


Short term /Monday through Tuesday night/... 
insentropic lift increases across the forecast area early Monday 
morning as a warm front lifts north across the area in advance of 
the approaching cold front. Very dry air will be in place when 
moisture associated with this warm front begins to fall...and the 
timing of the onset of the precipitation in the west will still be 
when surface temperatures are at or below freezing. Because of this 
and the expected wet-bulbing to below freezing aloft...there should 
be a few spots in the mountains early Monday morning with some sleet 
or freezing rain. By middle-day Monday...all areas will be warm enough 
for rain showers to be falling. 


The cold front will sweep through the area Monday evening...and with 
it increasing winds...initially primarily from the west. As colder 
air enters the region...expect a transition from rain to snow in the 
mountains...and precipitation to end east of the Blue Ridge. With a 
westerly wind...upslope conditions will not yet be maximized...and 
with a rain to snow transition in most locations occurring after 
midnight...not expecting notable snowfall during this period. 


Temperatures will probably stay under freezing in the mountains in 
most locations Tuesday allowing for snow showers to continue. 850 mb 
winds will slowly veer to west-northwest during the day and increase 
to near 40 kts...and by the evening...to northwest. From the late 
afternoon Tuesday into Tuesday night will be when we will start to 
see upslope snows begin to maximize. East of the Blue Ridge...this 
region will be dominated by downslope conditions with limited cloud 
cover and milder temperatures in the 40s on Tuesday. 


&& 


Long term /Wednesday through Saturday/... 
12z GFS and CMC plus 00z ec model all show deep upper vortex 
centered over New England or upstate New York at the outset of the 
extended period. Models all drift the upper low very slowly NE 
into southern cananda. A major Thanksgiving snowstorm likely for 
somwehere in the northeast...possibly western New York. Main effect here 
will be persistent northwest flow with snow showers continuing into Wednesday 
in the favored locations of the western County Warning Area. Temperatures to 
remain very chilly through Thursday with some amelioration on Friday 
as short-wave ridging occurs ahead of the next complex trough 
digging into the middle-Mississippi Valley Friday. GFS shows surface 
low development in association with this feature tracking into the 
Ohio Valley by Saturday. This would put the County Warning Area in the warm sector 
of the cylcone over the weekend but way too early to do anything 
but broad brush increasing clouds in the grids. 


&& 


Aviation /11z Sunday through Thursday/... 
VFR conditions are forecast to prevail through at least 12z 
Monday...as high pressure lingers just east of the area. Expect 
some increase in middle/high clouds western sites late tonight well 
in advance of a cold front...otherwise mainly clear today into the 
overnight. 


Cold front arrives Monday with a chance of mainly daytime rain 
showers most spots...and a changeover to snow showers southeast wva sites 
Monday night. Dry low levels Monday may also delay sub-VFR ceilings 
and visibilities until midday or afternoon. Then strong northwest flow develops 
Monday night and Tuesday resulting in MVFR/IFR ceilings/visibilities at 
kblf/klwb in low clouds and oncl heavy snow showers into Wednesday. High 
pressure should finally build in on Thursday with a return to VFR 
conditions. 


&& 


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


&& 


$$ 
Synopsis...jh/ph 
near term...jh 
short term...ds 
long term...pc 
aviation...jh/js/ph