688 
fxus61 krlx 201011 
afdrlx 


Area forecast discussion 
National Weather Service Charleston WV 
611 am EDT Sat Mar 20 2010 


Synopsis... 
high pressure remains in control through tonight. Low pressure 
system passes Sunday night and Monday...with showers lingering 
Monday night into Tuesday. Warmer and drier Wednesday. 


&& 


Near term /through tonight/... 
high pressure will move eastward today. Still enough ridging to 
keep skies mostly sunny today. Some high clouds will will be 
scattered around out ahead of a storm system over central U.S. As 
the high continues to move eastward...moisture increases as well 
as clouds tonight. Blended guidance today for highs...keeping 
cooler temperatures in the mountains with some snow still on the ground 
above 3000 feet and slightly cooler west with more high clouds 
around. Lows tonight will generally be warmer than previous nights 
with increasing clouds. 


&& 


Short term /Sunday through Tuesday night/... 
short wave trough digging southeastward through southwestern states early this morning closes 
off tonight...then passes S of the area as it rolls across the Tennessee 
Valley sun nt...the Carolinas Monday and Monday nt...and then off the 
middle Atlantic Seaboard Tuesday nt. This puts the forecast area in the 
diffluent area NE of the upper low with good upper divergence much of the 
time Sun afternoon through Monday. This is coupled with intense qvec con 
and frontogenetic forcing late sun nt through Monday. 


This forcing is accompanied by sharp low level Theta-E ridge ahead 
of negative tilt occlusion that passes NE through the area Monday. 
Inserted thunder Monday with this. Otherwise...limited thunder to a 
small chance over S half of area sun evening with timing getting too 
slow to take advantage of diurnal heating Sunday. Gusty winds and a 
sharp though not large drop in temperature should follow the 
occlusion as the tropopause drops to middle levels just S of the area behind 
the occlusion Monday afternoon. 


Using a blend of guidance...came up with one half inch to an inch 
total quantitative precipitation forecast with this system...mostly sun nt and Monday but also 
including another shot behind the then exiting system Monday nt into 
early Tuesday. While this itself should not convert to excessive 
rainfall...would not be surprised to see higher quantitative precipitation forecast output in future 
runs given vigorous upper low passing S of the area and the 
coalescence of forcing parameters. If that pans out...up to a foot 
remaining snow / up to three inches water equivalent / over the 
higher terrain is available for release. The combination could 
warrant a Flood Watch for the northern mountains. As we saw from 
the system of a week ago...the key is 
location...location...location. The Rex block that played a crucial 
role in keeping the precipitation suppressed to the S for a critical 
time period during the last system is notably absent with this one. 
The slower and slower timing on this system with each passing day is 
also a bit unnerving. 


With the slower timing...preferred higher end of guidance for highs 
sun. Beyond that...used low level temperature fields from the nam12 
sun nt through Monday night with the baroclinic zone associated with 
the occlusion...together with cloud cover and 
precipitation...trumping diurnal trends. Did smooth out the tight 
gradient for Monday on account of timing uncertainty from this 
distance...even though a sharp gradient is likely. Blended in the 
European model (ecmwf) for highs Tuesday and the adjmex for highs Wednesday to lower in both 
cases to reflect slower exodus of the early week system. Lows Tuesday 
nt needed only minor adjusting...mainly to lower a bit over the 
higher terrain. Even with that...model soundings and low level 
temperature fields suggest any snow should be limited to the higher 
terrain Monday and Tuesday nights...with the precipitation winding down the 
latter night. 


&& 


Long term /Wednesday through Friday/... 
the upper level low continues to slowly track eastward...with the 
surface low moving through the Ohio River valley and will be east 
of our area by Tuesday morning. Higher probability of precipitation linger over the eastern 
high terrain in WV through Monday night. 


Given the previous model disagreement over the large pattern...the 
models have a surprisingly moderate level of agreement with the 
large pattern throughout the remainder of the extended 
forecast...therefore the extended forecast was equally influenced by 
the European model (ecmwf)...GFS...and HPC guidance. High pressure will begin to 
settle in Tuesday...and it will bring warmer daytime temperatures 
and drier conditions with it. Skies will be clearing as the system 
approaches...daytime highs will reach above 60...except in the 
higher elevations where daytime highs will be in the lower to middle 
50s. Skies will clear at night and radiational cooling will cause 
nighttime lows to be in the upper 30s and lower 40s. 


The chance of precipitation will return late in the week with the 
approach of the next shortwave trough...the most likely chance of 
precipitation will occur Friday afternoon. 


&& 


Aviation /12z Saturday through Wednesday/... 
12z Saturday to 12z Sunday... 
high pressure in control...with VFR conditions throughout. 
Scattered cirrus today. After 00z...increase in high to middle deck 
clouds towards 06z and broken 5000 to 8000 towards 12z...as next system 
moves towards the region. 


After 12z Sunday... 
brief IFR possible in showers/isolated thunderstorms Sunday 
afternoon and night. 


&& 


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


&& 


$$ 
Synopsis...trm/js 
near term...js 
short term...trm 
long term...mdp/jem 
aviation...js