Weather

735 
fxus61 krnk 061404 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
1004 am EDT Monday Oct 6 2008 


Synopsis... 
a back door cold front will continue to slide south through the 
region today as cool high pressure builds across the middle Atlantic 
region tonight through Tuesday. The high should begin to weaken 
and slide offshore by midweek ahead of a complex low pressure 
system that will affect the area later Wednesday through Friday. 


&& 


Near term /until 6 PM this evening/... 
surface winds area beginning to pick up from the northeast and 
bring some stratus through central Virginia. Otherwise just middle 
and high clouds expected for the rest of the day in the northern 
County Warning Area. Made slight adjustments to highs today based 
on current observations and the latest lav guidance. 


&& 


Short term /6 PM this evening through Wednesday/... 
surface high begins to really wedge in overnight with east/NE onshore 
flow deepening/increasing. This should eventually lead to some low 
clouds along the eastern slopes late with deck spreading SW by Tuesday 
morning. However given the strong ridging...may just be enough dry 
air to limit strato-cumulus to just a scattered layer so didnt go as cloudy 
as the NAM across the County Warning Area. Otherwise stayed on the cooler side of MOS 
overnight espcly NE half where colder surface-850 mb air will 
reside. 


High should bridge down east of the Blue Ridge Tuesday with the 
low level flow turning more southeast under strong short wave ridging aloft. 
This combo with heating should support gradually mixing out any 
morning low clouds with only the far SW possibly holding a low 
deck into the afternoon. Airmass though is pretty cool and if 
clouds get stuck could be a rather chilly day similar to the quite 
cool met MOS. Since expecting more sun leaned temperatures toward the 
warmer mav MOS or similar to the ensembles given such a large 
spread in Tuesday highs. 


For Wednesday...upper low to the west will begin to push its warm 
advection/isentropic lift precipitation shield toward the area as ridging 
slips offshore. Models continue to take best lift around the 
leftover pocket of dry air over much of the region with mainly 
increasing clouds overtop a dryish boundary layer per forecast 
radiosonde observations. May be enough relative humidity transport to get some -ra to the ground 
far western zones but iffy elsewhere given wedge and mainly 
middle deck overtop a dry layer until late. Thus cut probability of precipitation back some 
east and only left in 20/30 probability of precipitation west for now. Under increasing 
clouds and east/southeast flow...kept temperatures in comp position between 
mav/met MOS...but cooler than the ensemble spread for now. 


&& 


Long term /Wednesday night through Sunday/... 
the main weather feature this period will be early on as the 
shortwave/closed low spins east through the area Wednesday night-Fri. 
May initially see some split in the precipitation Wednesday night given 
lingering dry air...lift passing by to the west and best 
instability well to the SW. Moisture then deepens as the upper low 
moves closer with the best chance of rain Thursday-Thursday night pending 
how much of this system works through or dampens out. Therefore 
since still some uncertainty playing chance probability of precipitation into late week 
with clearing taking place by the weekend as the models send this 
system to the coast by Friday night. High pressure sliding east into 
Great Lakes Saturday will bring cooler temperatures and drier weather. The 
flow will turn northeast/east by Sunday and could see some showers 
pushing toward the area and increased clouds. Raised highs some 
next weekend per temperatures aloft and a drier wedge...but below latest 
00z GFS MOS which was based on increasing SW flow ahead of the 
next front and building heights. 


&& 


Aviation /14z Monday through Friday/... 
high pressure over the area will maintain VFR conditions today with 
the exception of fog along area rivers early this morning. Again expect 
dense fog with a period of LIFR possible at klwb between 11-13z 
this morning. Patchy MVFR fog is also likely at Dan and possibly 
lyh. Otherwise some ac possible from klwb-klyh into this afternoon with 
only cirrus likely elsewhere today. 


A back door cold front comes through the area later today bringing 
the lower level winds briefly around to the north then northeast. 
The surface winds should remain below 10 knots but the winds just 
above the boundary layer increase up to 25 knots behind the front 
suggesting a period of low level wind shear possible tonight...but left out of the 
tafs at this time until more confident on outcome. 


With the return of a cooler airmass Tuesday and Wednesday...fog 
formation is again likely in the mountain valleys each 
morning...dissipating between 13-14z. Rain will be moving into 
the area by Thursday and then lingering into Friday. 


&& 


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


&& 


$$ 
Synopsis...jh/wp 
near term...air mass 
short term...jh/wp 
long term...jh/wp 
aviation...jh/PM