706 
fxus61 kpbz 220205 
afdpbz 


Area forecast discussion 
National Weather Service Pittsburgh PA 
905 PM EST Friday Nov 21 2008 


Synopsis... 
with the cold winds off the Great Lakes having turned from 
northwest to west the remaining snow showers will be confined to 
western Pennsylvania areas north of Pittsburgh. Temperatures will 
be cold through much of next week. There may be another bout of 
snow starting Monday as a low pressure system moves through the 
Great Lakes. 


&& 


Near term /through Saturday/... 
judging from blend of recent radar data and sref model runs and 
NAM profiles...expect the remaining bands of lake effect snow 
showers to be confined to western Pennsylvania areas north of 
Pittsburgh the rest of tonight. This is because the surface layer 
winds have shifted into the west and surface layer instability 
is becoming capped below 8 kft above ground level. So have ended the winter 
storm warnings for the mountains...while continuing the lake 
effect Snow Advisory for the I-80 corridor into late Saturday. 
Forecasted temperatures lower than blend of GFS and NAM MOS due 
to radiative effects of recent snow cover. 


&& 


Short term /Saturday night through Sunday night/... 
recent sref model runs show high pressure will pass to the south 
Saturday evening into Sunday morning...bringing southwesterly flow 
and drier air. So Sunday will be dry and relatively cloud free. 
Forecasted temperatures could be a colder than NAM and GFS MOS 
values depending on extent of snow cover and its effect on radiative 
processes. 


&& 


Long term /Monday through Friday/... 
blend of recent gefs and European model (ecmwf) model runs have been consistent in 
showing upper level Pacific coast ridging next week that would keep 
a cold trough in the east. Hence expect temperatures to remain below 
normal as shown by GFS MOS and HPC guidance. Late week around Friday 
the upper flow may split so that the upper Ohio Valley may be more 
influenced by a not so chilly southern branch. 


Regarding precipitation prospects a Canadian low pressure system 
moving through the Great Lakes can bring another round of snow 
starting Monday. 


&& 


Aviation /02z Saturday through Wednesday/... 
based on recent trends in radar data and NAM profile wind 
directions...have amended tafs to no longer forecast tempo IFR 
conditions for sites south of the western Pennsylvania I-80 
corridor. Stratocumulus ceilings will be likewise intermittent and 
be mainly in the VFR range. Winds through Saturday will be mainly 
westerly at 7-10 kts. 


High pressure will build into our area for Saturday and 
Sunday...with mainly VFR conds expected. Next chance for IFR 
conditions will come with the passage of a low pressure system 
through the Great Lakes Monday into Wednesday. 


&& 


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


&& 


$$