423 
fxus61 krnk 092051 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
351 PM EST Friday Jan 9 2009 


Synopsis... 
high pressure slides to the Outer Banks tonight as a warm front 
lifts through the Ohio Valley on Saturday. An area of low pressure 
will track into southwestern Pennsylvania late Saturday...as a 
cold front is shoved across the Blue Ridge Sunday morning. High 
pressure again covers much of the middle Atlantic on Monday 
before another cold front enters Tuesday. 


&& 


Near term /through Saturday/... 
next wave with upper system coming out of The Rockies will head 
NE into the middle miss valley late tonight as high pressure weakens. 
Main warm frontal lift should slide north overnight in response to 
increasing SW jet aloft while channel of deeper relative humidity with surface low 
shifts toward the Ohio Valley after midnight. Expect moisture to be 
far enough west to allow for clear skies much of the night...so 
took MOS temperatures down a bit. 


Trailing frontal type precipitation band will approach very late. Latest 
models continue to come in line with a slower arrival of best 
lift. This would alleviate nearly all of the late night and early 
morning icing concern west. Continued to trim back coverage by a few 
hours in the west but still left in slight chance -fzra early Sat 
morning across Greenbrier valley / I-64 corridor. Otherwise increasing 
clouds west late on the leading edge of the upward vertical velocity while remaining 
mostly clear out east. Temperatures steady or rising into the middle/upper 30s 
on the ridges late under strong warm advection aloft...while the 
valleys and east likely fall off into the middle/upper 20s before any 
clouds arrive. 


Isentropic lift with associated moisture increases from west to 
east across the region on Saturday as a warm front lifts north 
across the region. Saturday afternoon a cold front will sweep 
through the region. Expect very good coverage of showers along the 
front with colder air moving into to the region behind it. 


&& 


Short term /Saturday night through Monday night/... 
good amount of dry air will be in place as swath of rain shws 
cross the County Warning Area Saturday night. Although model quantitative precipitation forecast estimates may be 
high...open gom should allow for precipitation to survive its battle with 
the dry air and westerly winds. Will hold onto low likely probability of precipitation for 
now. Storm moving through Pennsylvania should lead to better 
delivery of cold air than usual around here...however the air isnt 
that cold for Jan...with the typical coldest GFS solution 
struggling to -10c. MOS numbers look a little low considering the 
above Sunday morning...and with clouds/winds holding up part of the 
temperature fall will be more due to wetbulbing than an actual diurnal 
trend. Expect a change to snow late and perhaps not until after 12z 
Sunday in the favored western upslope areas...and a quick light 
accumulation could occur in those spots. Downsloping will take the 
edge off of the cold air along the lower territory. Op GFS seems 
to be an outlier with the speed of the front and clipper prognosticated 
for next Tuesday in comparison to the sref...so slowed down probability of precipitation 
into 12z Tuesday and lowered temperatures a bit considering some 
Southside spots may be able to decouple that night. 


&& 


Long term /Tuesday through Friday/... 
a cold front is expected to slide across the region Tuesday morning 
with mountain snow showers possible into Tuesday evening. There is 
some brief Great Lakes connection to have accumulating snow on 
western slopes of around an inch or two. Will also leave chance 
probability of precipitation in the east during the morning...just in case timing of system 
slows down. Overnight Tuesday...a high pressure will be centered 
over the southeast US with all snow showers ending by midnight. 
After midnight Wednesday...a warm front track to the North. Place of 
the isentropic zone is along the Mason-Dixon line to not have any 
measure precipitation in the area. Trace amounts are possible and it could 
fall as a winter mix...therefore will keep a mention of probability of precipitation across 
the mountains. Through the day Wednesday...the area should remain in 
the warm sector with a cold front arriving late. Upslope snow 
showers will again plaque the western slopes through Thursday 
morning. A strong Arctic high pressure system will move from the 
central US to the East Coast starting Friday. The region will remain 
cold and dry through the weekend. 


&& 


Aviation /21z Friday through Wednesday/... 
looking at VFR conds across the region with light winds through 
tonight. Clouds lower during the morning hours tmrw...but think 
MVFR conds and precipitation will hold off until afternoon...just a very small 
chance of seeing precipitation before noon on the western slopes. And if it 
comes in early enough may encounter some temperatures near freezing...but again 
an outside chance. 


Expect widespread showers Sat afternoon...then with upslope 
rain/snow showers developing will likely keep low ceilings/visibilities at 
kblf/klwb Sat night before drier air works in by Sunday morning. 
High pressure builds in on Sunday resulting in VFR conditions for 
the end of the weekend into early next week. 


&& 


Hydrology... 
Flood Warning continues for the Dan River at South Boston. 


&& 


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


&& 


$$ 
Synopsis...km 
near term...jh/js 
short term...km 
long term...rcs 
aviation...jh/js 
hydrology...