Weather

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fxus61 krlx 052348 
afdrlx 


Area forecast discussion 
National Weather Service Charleston WV 
622 PM EST Monday Jan 5 2009 


Synopsis... 
large storm system impacts area tonight through Wednesday...which 
will include possible ice and water problems for portions of the 
area. Rain changes to snow into Wednesday night and Thursday. 


&& 


Near term /through Tuesday/... 
as expected...the large contrast in the outdoor environment is 
over our County Warning Area this Monday afternoon. From near zero visibility in 
fog to sunshine and Bone dry with dew points in the teens. 


Freezing rain is still a concern...but have shifted the main 
concern into interior southeast Ohio late tonight and Tuesday 
morning...rather than in our eastern counties. 


12z models a bit faster lifting deeper moisture back north into 
the colder air. Plus the coldest air that is pooling east of the 
mountains appears to be setting up from the Potomac Highlands on 
NE into PA...not as far south as the Greenbrier valley. 


In our County Warning Area...the air is the coldest and driest in southeast Ohio. Still 
thinking some freezing rain could develop over Randolph an Pocahontas with 
easterly flow developing...but not severe. So will likely have the 
watch lead to an advisory there...not a warning. 


Still developing our specific details for the late afternoon 
release...but will likely Post an advisory for late tonight and 
Tuesday morning across several of our western and northern 
counties...for the possibility of a brief of freezing rain...will 
hold the headline a bit longer north of Uni. 


Will likely hold off on any water headlines. We can handle any of 
the rain overnight and we still have time to monitor the developments 
this evening and overnight. 


&& 


Short term /Tuesday night through Wednesday/... 
relied mostly on GFS/sref for synoptic setup...as 12z NAM seemed 
like an outlier with handling of northern stream and surface 
reflections. Main issue Tuesday afternoon through Wednesday will switch from 
winter weather to excessive rainfall. Models have shifted a little south 
than previous runs with placement of deeper moist. 850 mb moist trans 
vec/mag within low level jet now depicted to pass mostly over 
Tennessee...western NC..and Virginia. As a result model quantitative precipitation forecast over area has 
decreased some. Even so...sref probability and GFS still show 2 inches 
across SW Virginia counties and southern WV mountains being somewhat removed 
from deepest moist...this quantitative precipitation forecast likely result of orographic enhancement 
on eastern slopes through strong ascent from easterly flow. Used HPC 
quantitative precipitation forecast which is very similar to those models. After looking at 
ffg/digesting sref probability contingency run from rfc/and coordination 
with mrx and rnk...decided to hold off on Flood Watch at this time...with 
bulk of quantitative precipitation forecast occurring Tuesday eve/night. Maintained mention in severe weather potential statement. 


Frontal passage looks to be around 18z on Wednesday...with decreasing probability of precipitation to high 
chance outside mountains/maintained Cat for mountains/ as backlash and beginning 
of impressive cold air advection commences. 


Ran a non diurnal throughout the period. Temperatures should be above freezing 
all places late Tuesday afternoon. Generally followed mav guidance...considering 
it was the model of choice. Temperatures will rise overnight Tuesday under 
strong warm air advection...and remain nearly steady until frontal passage Wednesday afternoon. Expect 
most places will fall into lower 30s by Wednesday evening...as strong cold air advection 
becomes realized. 


&& 


Long term /Wednesday night through Monday/... 
cold air dives into the region behind the cold front...dropping 
temperatures and causing any lingering rain showers to change to 
snow. Initially...may not see much snow shower activity early 
Wednesday night...but a strong shortwave...associated with an upper 
level low will swing across the region...deepening the moisture and 
also providing enhanced vertical motion. So expect that the snow 
shower will intensify after midnight and could even lead to some 
accumulations in The Lowlands. Right now the track would favor the 
best chance for accumulating snow across northern WV into the mountains. 


On Thursday into Thursday night...expect to see a good period of 
snow showers in the favored upslope regions as the moisture 
depth...especially on Thursday...is still up through 700 mb and the 
core of the 850 mb cold air is over the region. The snow showers 
will taper off Thursday night as high pressure finally builds into 
the region. 


High pressure maintains control Friday into Friday night...with some 
warm advection developing ahead of the next frontal system. The GFS 
continues to be faster with this front than the European model (ecmwf)...but the 12z 
run did slow down from previous runs and is getting closer to the 
European model (ecmwf) timing. So tried to bank on the highest probability of precipitation between about 9z 
Sat and 18z Sat. Did not go as high as HPC for two reasons...one 
being uncertainty on the timing...but also because of the track of 
the low going to the north...could see the best dynamic lift going 
to the north...which would be the focus for the precipitation. The 
other change with the precipitation was to make it all rain ahead of the 
front. Timing will be a big factor as to how cool it gets ahead of 
the front...but did feel that with the southerly flow...that cold 
air should not get trapped...except maybe east of the 
mountains...but with the slower timing...temperatures should be able 
to be above freezing everywhere when the precipitation arrives. 


Behind the front on Saturday night...the cold air again dives into 
the area...but the moisture depth behind this system is less so the 
chances for the accumulating snow showers will be lower. It will 
still be cold as both models show 850 mb temperatures again falling 
down to around -14c or colder. This will mean that Sunday will 
again be cold with some snow showers/flurries possible. At the 
surface high pressure will build into the area so expect a cold 
night Sunday night...especially if the sky clears. 


On Monday...the pattern begins again with warm advection again 
developing across the Ohio Valley as the next shortwave trough 
approaches. Both 12z model runs now develop a stronger surface 
cyclone with this next wave and the GFS even tries to phase the northern 
and southern stream to push more Gulf moisture northward. The 00z runs 
were less enhanced...but did bring a clipper type shortwave across 
Monday night. So have allowed for some low probability of precipitation late Monday and 
then began to increase them Monday night. 


For temperatures...generally ran with a blend of the 12 mex and the 
HPC guidance...taking into account the timing differences between 
the models. 


&& 


Aviation /00z Tuesday through Saturday/... 
big gradient across the region with LIFR conditions in southern 
counties and VFR conditions in the northwest. As a storm system 
moves toward the region overnight...ceilings will be lowering in the 
north. Freezing rain is possible in northern portions of the area 
later tonight. Expect widespread IFR/LIFR conditions on Tuesday with 
rain...and some freezing rain in the north. However...some locations 
on the immediate western slopes could see some improved conditions 
on Tuesday due to downsloping. 


Aviation outlook /beyond 00z Wednesday/... 
widespread IFR in ceilings and precipitation Tuesday night. 


&& 


Hydrology... 
rain may be heavy at times Tuesday and Tuesday night...possibly 
bringing flooding problems. If the flood threat increases...flood 
watches would be posted for the most vulnerable counties. Continue 
to have in hazardous weather outlook. 


&& 


Rlx watches/warnings/advisories... 
WV...Freezing Rain Advisory from 1 am to 12 PM EST Tuesday for 
wvz007>011-016>020-029>032-039-040-047. 
Freezing Rain Advisory from 1 am to 3 PM EST Tuesday for 
wvz046. 
Ohio...Freezing Rain Advisory from 1 am to 12 PM EST Tuesday for 
ohz076-083-085>087. 
Winter Weather Advisory from 4 am to 3 PM EST Tuesday for 
ohz066-067-075-084. 
Kentucky...Freezing Rain Advisory from 1 am to 12 PM EST Tuesday for 
kyz101-102. 
Virginia...none. 


&& 


$$ 
Synopsis...ktb 
near term...ktb 
short term...30 
long term...ess 
aviation...rpy 
hydrology... 

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