056 
fxus61 krlx 192006 
afdrlx 


Area forecast discussion 
National Weather Service Charleston WV 
305 PM EST Wednesday Nov 19 2008 


Synopsis... 
high pressure in control through early tonight. A warm front moves 
through overnight...followed by a cold front Thursday morning. 
Upslope snows follows into Friday. High pressure returns for the 
weekend. 


&& 


Near term /through Thursday/... 
skies are expected to clear from west to east this evening...as the 
high pressure still in control. Models show some warm advection at 
h850 as a warm front passes through overnight. Only and increase in 
clouds is expected with this feature. Then...a cold front passes 
through Thursday morning increasing chances for mixed precipitation western 
slopes or snow showers at higher elevations Thursday afternoon. 


Cold front move east of the Appalachians by Thursday afternoon. 
Then...northwest flow sets in providing the forcing for upslope snow 
showers to start...with less moisture and intensity than previous 
snow event. 


With clearing invading from west to east this evening...radiational 
cooling will take place dropping temperatures below all guidance 
tonight mainly west and southern sections...and over areas with snow 
cover. Areas with both conditions will be the coldest. 
Therefore...went generally colder than guidance although closer to 
met across the northeast mountains as clouds will linger longer 
there. 


H850 warm advection should bring highs to around 40f 
lowlands...ranging into the middle 20s Highlands. 


&& 


Short term /Thursday night through Saturday/... 
good cold air advection and northwest flow behind cold front...coupled with energy 
rotating around the upper trough and a brief period of good isentropic 
lift between 06z and 12z Friday...will set up a possible upslope 
snow event Thursday night into Friday. Moisture is limited...but may 
need a watch or an advisory for that time period. Again...the higher 
elevations should see the most snows lesser amounts elsewhere. The 
Lowlands could see less than in inch to a dusting. Limited moisture 
decreases on Friday and snow showers should diminish throughout the 
day on Friday. 


Temperatures will be below freezing at the surface...as 850 mb temperatures 
Thursday night are between -8 to -11 and will continue to decrease 
by Friday morning. -13 to -16 to start out the day Friday and will 
remain throughout on Friday. 


Ridging starts Friday night and Saturday as high pressure build in 
over the region. This will start to clear skies and cut off any 
snow shower activity. A gradual warming will start to take hold on 
Saturday with more sunshine. 










&& 


Long term /Saturday night through Wednesday/... 
while the overall trend of the models is pretty consistent in 
forecasting a shortwave ridge over the Ohio Valley on Sunday and 
then another strong trough/closed low scenario for Monday through 
Wednesday. But of course...there are many differences in timing 
along with movement of the closed low and trough. The 12z GFS has 
trended a little further south and slightly faster from its previous 
run with the movement of the closed low and shortwave trough. As a 
result...it is faster to get the front into the area on Monday...but 
still during the day on Monday. The 12z European model (ecmwf) is still faster than 
the GFS...but not quite as fast as the 00z run. So it appears that 
the models are starting to come to a consensus that the front will 
hold off until the day on Monday to push into the region. So as a 
result have slowed the progress of probability of precipitation on Sunday night...but do 
allow for at least slight chance probability of precipitation everywhere by 12z to account 
for timing difference. But the interesting item here is the precipitation 
type as both models show 850 mb temperatures above freezing so not 
expecting snow ahead of the front...but could potentially see some 
freezing rain in the sheltered valleys in the mountains...assuming 
the radiational cooling early in the night gets temperatures below 
freezing. At this stage did not go with freezing rain...but it is 
possible if the precipitation arrives early. 


Have raised probability of precipitation to around 50 percent on Monday with the front...and 
then behind the front...it may take a 6 to 12 hour lag behind the 
front for the cold air to arrive...but conditions again look good 
for upslope snow Monday night through Tuesday night as a long period 
of northwest flow...deep moisture and 850 mb temperatures between 
-8c and -10c move into the region. So have raised probability of precipitation through 
Tuesday night in the favored upslope regions to 40 percent. 


The upslope finally wanes on Wednesday as the upper low pulls away 
and the moisture depth decreases. So allow the probability of precipitation to taper off in 
the mountains with dry weather elsewhere. The models are struggling 
to handle the movement of the upper low beyond day 7 as the European model (ecmwf) 
tries to leave the closed low behind through day 10...but since the 
00z run had it off the NC coast and the 12z run has it over New 
England...not having much confidence in it at this point so have 
followed more with moving the trough east and allowed for dry 
weather into Thursday morning. 


For temperatures...raised values some on Sunday highs...but probably 
not enough. 12 mex is in the low 50s now and based upon the 850 mb 
temperatures those values are reasonable. Also...went a little milder on 
Sunday night with the SW flow ahead of the front. On Monday...the 
timing of the front will be the deciding factor on the highs so have 
blended between the mex numbers and the faster timing of the European model (ecmwf) 
which would hold temperatures down. 


For Monday night through Wednesday...went colder than the guidance 
for highs as the northwest flow...clouds and snow showers will hold temperatures 
down during the day...but held close to the numbers on the lows as 
the clouds should hold lows up a touch. 


&& 


Aviation /19z Wednesday through Monday/... 
VFR conditions will prevail at most sites through tonight. High 
pressure in control keeping dry and cold conditions. Upper level 
clouds will move through the area through this evening. Areas of 
clearing will affect heights...pkb...and crw this evening and could 
spread east to reach the central eastern mountains and perhaps bkw 
tonight. 


The southwest flow increases after 09z...and ceilings will start to 
lower to 5 kft or so from west to east...in response to the approach 
of a warm front...with MVFR ceilings possible near dawn Thursday. 


Aviation outlook /beyond 18z Thursday/...IFR conditions possible in 
the mountains in snow showers Thursday night into Friday. 


&& 


Rlx watches/warnings/advisories... 
WV...none. 
Ohio...none. 
Kentucky...none. 
Virginia...none. 


&& 


$$ 
Synopsis...arj/ess/js 
near term...arj 
short term...js 
long term...ess 
aviation...arj 

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