799 
fxus61 krnk 221720 
afdrnk 


Area forecast discussion 
National Weather Service Blacksburg Virginia 
1220 PM EST Sat Nov 22 2008 


Synopsis... 
cold high pressure just west of the mountains will build east 
across the the area today and tonight before passing slowly 
offshore by Sunday night. Another cold front will move through 
Monday followed by cold northwest flow and mountain snow showers 
Monday night into Tuesday. High pressure should finally build in 
for middle and late next week. 


&& 


Near term /through tonight/... 
only minor changes were made to todays forecast. Brought down 
high temperatures a couple of degrees today as 15z readings are 
running below guidance forecast values and with middle/high level 
clouds currently moving into eastern Kentucky in advance of a dampening 
upper level shortwave...expect clouds to increase late this 
afternoon. 


12z upper air soundings indicated 30+ knots jet between 900 and 850 mb...so 
increased wind gusts for this afternoon. As surface ridge across Kentucky/Tennessee 
moves east later today...wind gusts should come down. 


For tonight...model relative humidity sections show cloud cover remaining 
overnight with clearing from northwest to southeast late as the vorticity passes. 
Just how fast any clearing takes place critical for low temperatures 
given ridge overhead and dry air. Since appears clearing wont 
happen most spots until very late...stayed closer to local scheme 
temperatures which remain a little above MOS...except northwest where earlier 
cloud exodus should spell colder middle/upper teens. 


&& 


Short term /Sunday through Monday night/... 
next significant upper trough begins to dig southeast toward the area by 
later Sunday preceded by short wave ridging and surface high exiting 
offshore. This should finally spell a period of warm advection 
aloft allowing all areas to recover back into the 40s to around 50 
southeast given return west-southwest flow and sunshine. 


Cold front approaches from the west late Sunday night and 
Monday...with frontal passage anticipated Monday evening. Models 
continue to be a bit slower with the precipitation...holding most spots 
off until Monday afternoon at this point per GFS/ensembles. 
However even with a slower scenario...dry air aloft/evaporative 
cooling may cause a start as snow/sleet espcly western zones 
before transitioning to all rain given such a strong 850 mb SW jet 
just ahead of the front. Otherwise slowing down precipitation arrival...but 
also boosting probability of precipitation to higher likelys/low end categorical west by 
afternoon...and good chance to low likelys east as decent slug of 
upward vertical velocity rolls through. 


After frontal passage Monday night...cold advection on strong 
winds races in changing rain to upslope snow showers with temperatures 
crashing back into the 20s and low 30s. 


&& 


Long term /Tuesday through Saturday/... 
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 /18z Saturday through Thursday/... 
VFR conditions are forecast to prevail through 18z Sunday...as 
gusty northwest winds midday Saturday subside later this afternoon as high 
pressure advances east into our region. An upper level area of 
low pressure will track southeast from the Missouri Valley this afternoon into 
the middle Atlantic tonight...which will bring middle and high level 
clouds this afternoon and tonight...but ceilings will be 10k feet 
or higher. 


Another cold front arrives Monday with chance of rain and snow 
showers into Monday night. Strong northwest flow will develop by Tuesday 
likely resulting in MVFR/IFR ceilings/visibilities at kblf/klwb in low 
clouds and snow showers. 


&& 


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


&& 


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