613 
fxus61 krnk 071755 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
1255 PM EST Wednesday Jan 7 2009 


Synopsis... 
high pressure wedged down the east side of the Blue Ridge will 
move out of the area today as a cold front moves through the 
region from west to east. A second cold front will swing through 
Thursday morning. 


&& 


Near term /through tonight/... 
12z soundings showed wedge this morning was 1000 to 3000 feet 
thick but it was quickly eroding from the west...with the higher 
wind gusts just above the inversion...in the 35 to 45 knot range 
starting to mix down to the surface. May expand Wind Advisory on 
the east and west sides before noon. As The Wedge breaks... 
temperatures are climbing into the upper 40s. 


May cut back chance of rain west of the Blue Ridge this afternoon 
as the forecast area gets in the dry slot. Not much precipitation 
was upstream in the Tennessee Valley. 


&& 


Short term /Thursday through Friday/... 
upslope relative humidity forecast to hang around longer than earlier thought on 
Thursday as will need to wait for a middle wave to pass through the trough and 
exit by Thursday night. With the flow turning a bit more northwest expect 
off/on -shsn to persist espcly northwest Thursday with clouds and perhaps 
flurries/sprinkles making it east of the Blue Ridge as vorticity tracks 
through. Will at least get some filling in of clouds east under 
increasing lapse rates so boosted clouds and lowered highs some 
across the region Thursday. Should finally clear out all areas Thursday 
night with upslope weakening and high pressure building in from 
the west...so only chance probability of precipitation early far west. Dewpoints in the 
teens and lighter winds will allow most to fall into the 20s Thursday 
night with some teens in the deeper valleys. 


Fast flow aloft should quickly push the ridge across and then southeast 
of the area Friday with some return flow warm advection developing 
in the afternoon. Very dry air under sunshine and weak SW flow 
will allow temperatures to return closer to more normal levels as the 
upper cold pool gives way later in the day. 


&& 


Long term /Friday night through Tuesday/... 
high pressure will slide off the southeast coast Friday night. 
Meanwhile...across the middle west and into the Ohio Valley...a surface 
low and associated cold front will be approaching from the west. At 
the moment...precipitation looks to hold off until 
Saturday...therefore I have back off on probability of precipitation. Model differences 
between the GFS and European model (ecmwf) making this weekends forecast a challenge. 
GFS is very fast and a lot colder than the European model (ecmwf) especially with 
ridging well to our west. Took HPC advice/guidance and leaned the 
extended towards the European model (ecmwf) with this weekends front coming through 
Saturday afternoon and evening. High pressure once again builds over 
the area to salvage at least a dry second half of the weekend. 
Despite the sunshine...cold temperatures in the 30s and windy 
conditions could make Sunday a little uncomfortable. For early part 
of next week...both models agree that the northern and southern 
streams are not in phase. Therefore chances of precipitation low but 
possible. 


There is no significant phasing within the global wind oscillation 
(gwo). However...the global atmospheric angular momentum anomaly 
(glaam) is showing a trend towards cooler temperatures next week. 


&& 


Aviation /18z Wednesday through Monday/... 
LIFR clouds and fog at lyh will scour out quickly this afternoon 
as wedge erodes and winds come around to the southwest with 
increasing wind speeds. Scattered showers will continue across the 
region this afternoon with MVFR ceilings and VFR to MVFR 
visibilities. Some snow may be mixed in with the rain...especially 
west of the Blue Ridge before 00z. 


Once the sun sets the precipitation will end east of the Blue 
Ridge and change over to snow in the west. Snow showers with MVFR 
to IFR ceilings and visibilities will continue at blf and lwb 
through at least 12z. After that the moisture becomes more 
shallow and the precipitation will end. 


Winds will stay gusty through the forecast period. On Thursday 
night and Friday high pressure over the area will result in much 
lighter winds. 


Another cold front comes through Sat which could bring brief MVFR 
conditions in light mixed winter precipitation on Sat. High 
pressure builds in on Sunday resulting in VFR conditions for the 
end of the weekend. 


&& 


Hydrology... 
Flood Watch for the Southwest Mountains through today...and the NC/Virginia 
foothills east along the Dan River basin through Thursday. 
Looking at another 1 inch possible...with the mountains getting 
the best slug of moisture this morning...and out east today main 
concern will be for small streams in the mountains and adjacent 
foothills flooding during the rain event...followed by main Stem 
flooding along the Dan River at the end of the rain event. 


&& 


Rnk watches/warnings/advisories... 
Virginia...Wind Advisory until 6 am EST Thursday for vaz007-009>020- 
022>024-032>035-043. 
Flood Watch through Thursday afternoon for vaz032-033-043-044- 
058. 
NC...Wind Advisory until 6 am EST Thursday for ncz001>003-018>020. 
Flood Watch through Thursday afternoon for ncz003-019. 
WV...Wind Advisory until 6 am EST Thursday for wvz042. 


&& 


$$ 
Synopsis...air mass 
near term...air mass 
short term...ams/jh 
long term...rcs 
aviation...jh 
hydrology...