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fxus61 kpbz 220727 
afdpbz 


Area forecast discussion 
National Weather Service Pittsburgh PA 
227 am EST Sat Nov 22 2008 


Synopsis... 
snow showers mainly north of Pittsburgh will decrease by tonight 
as winds shift to the southwest. After a cold night tonight...high 
pressure will provide for dry and not as cold conditions for Sunday 
and Sunday night. Large low pressure will affect the area Monday 
through midweek...bringing scattered to numerous snow showers. 


&& 


Near term /through tonight/... 
radar continues to show bands of snow stretching from northern 
Allegheny County to southwestern New York...with significantly reduced 
visibility across areas north of I-80. Will continue the lake 
effect Snow Advisory for Forest...Venango and Mercer counties 
through this afternoon. Areas to the south will remain mainly dry...with 
perhaps a few morning flurries/isolated snow showers along a 
bvi/pit/lbe line. 


For Sat night...will go below model guidance for most areas as 
skies will become mostly clear overnight. Single digits are 
likely across the deepest snow cover areas across the ridges...with 
low teens north of I-80...and middle teens for the Ohio Valley. 


&& 


Short term /Sunday through Sunday night/... 
high pressure will cross the region with dry and mostly clear 
conditions. Winds will become S/SW...which will result in some 
modification of the air mass...but existing snow cover will be 
a limiting factor. Thus...will go under guidance...with low/middle 
30s north...to the lower 40s in the snow cover free south. 
Clouds will begin to increase Sunday night ahead of the next 
significant system...allowing for limited cooling...with lows 
mainly in the 20s. 


Long term /Monday through Friday/... 
models coming into general agreement for a rather stormy week. 
A frontal system will approach the area Monday...crossing the 
area Monday night. Precipitation will begin across eastern Ohio 
Monday morning...spreading east Monday afternoon. Given decent model 
agreement and run to run continuity...will increase probability of precipitation Monday 
afternoon/night to likely/categorical for all areas. Thermal profiles 
suggest initial precipitation across eastern Ohio Monday morning will 
likely be snow but then quickly change over to rain...with all 
liquid for SW PA/points south and east Monday. North of I-80...precipitation 
could mix at times with snow. Colder air will work back in behind 
the front Monday night...changing precipitation back to snow. For Tue/Wed... 
both GFS/European model (ecmwf) show the upper low stalling just to the NE...with 
significant moisture in northwest flow remaining over the area. Position 
of the low will be critical for snow potential...but for now will 
increase the north and ridges to likely Tue/Wed...with chance probability of precipitation 
further southwest. Precipitation will begin to diminish Thanksgiving day 
as the low is prognosticated to move into New England...with dry conditions 
for Friday. 


&& 


Aviation /07z Saturday through Wednesday/... 
as a northwest flow continues lake effect snow showers will persist 
across mainly northern terminals through this morning...reducing 
conditions to IFR at times. Meanwhile...high pressure will build in 
from the southwest for southern terminals. This high will bring an 
end to lake effect snow showers over area terminals this evening. 
This high will provide for VFR conditions through Sunday night. A 
low pressure system will develop and move east toward the region on 
Monday. This system has the potential to develop into a winter storm 
over the East Coast by middle week. Therefore precipitation...and 
reduced conditions will be possible anytime Monday afternoon through 
Wednesday. 


&& 


Pbz watches/warnings/advisories... 
Maryland...none. 
Ohio...none. 
PA...lake effect Snow Advisory until 6 PM EST this afternoon for 
paz007>009. 
WV...none. 


&& 


$$