260 
fxus61 kctp 221137 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
737 am EDT Monday Mar 22 2010 


Synopsis... 
low pressure will move into southwestern Pennsylvania by late 
afternoon and continue eastward to Long Island by Tuesday 
afternoon. High pressure will move in from the west for Wednesday 
and Thursday. A weak area of low pressure should pass to the south 
of the state late in the week. At the same time...a strong high 
pressure area will drop out of the Canadian plains into the 
northeastern states. 


&& 


Near term /until 11 am this morning/... 
moisture aloft continues to climb as Erly flow brings in Atlantic 
moisture. Dry air already wrapping into the upper low. One spoke of 
vorticity is rolling into southwestern PA...but forcing weaker to the 
east. Showers are already spreading nwrd across the southern tier and 
should expand and cover our forecast area this morning...so high probability of precipitation 
seem in order for the near term. Rainfall should be more- showery 
than constant rain...so some places may only get a few hundredths 
while southern/western areas could pick up to a quarter of an inch. Expect 
coverage and amounts to be better/higher in the west...and more- 
scattered and lighter in the east. As was the case during the 
long winter season...the local WRF run continues to impress with 
timing and quantitative precipitation forecast during the first 24 hours even as we move into the 
warm-season and transition to convective and liquid precipitation. 
Stability remains high with this first shot of showers...so will 
keep T out of the forecast for the near term. 


&& 


Short term /11 am this morning through Tuesday night/... 
dry air punch moving into the southern tier this afternoon/evening will help 
to bring Li/S to negative values aloft and very close to or just below 
zero from the surface during the afternoon. 800 mb winds will be 35kts from 
the south-southeast. So...will continue to mention chance T into the early 
evening in across all of the southern half. Arrival of the better 
forcing will be later in the afternoon/evening in the north...and surface 
temperatures will be lower there...so will cut off the mention of T for 
places north of unv. Precipitation through the event seems to get near an inch 
in the east...but only a half to three quarters of an inch in the 
west. While this will be a soaking...the recent dry stretch has 
allowed the waterways to drop well...and the lack of snow pack will 
help to make flooding a non-concern. 


Diurnal range today will be interesting to watch...as any sun in 
the S will poke those locations into the u60s. Most of the rest of 
the area will see temperatures only rise a few degrees from this morning/S 
balmy levels. 08z temperatures are about 10f greater than normal maxes 
this time of year. Ipt was 19 degrees above normal Sunday. We are 
certainly on-track for one of the very warmest marches on record 
for the entire region. 


Tonight...the low moves across the state from west-east and the showers 
will taper off in the southeast and then the east. The Western Hills will still 
have some rain showers to deal with all night...but they will be light and 
more-scattered than during the day. Mins may fall tonight -- but 
the clouds and the fact that the coldest 800 mb air slides under the 
state /over Virginia/ instead of over top of US will work against it. 
Will go for mins in the u30s north and M-u40s S/E. 


7h low passes just to the south of the state Tuesday as trough axis 
swings through. With cool air aloft and moisture wrapped around the upper 
low...will carry likely probability of precipitation area wide. Maxes will be closer to 
normals...but just a shade above. Moisture tapers off as subsidence 
inversion from wide-reaching high to the west squashes it lower and 
lower Tuesday night. Will continue to keep a mention of dz for the 
northern/western zones and possibly some wet snowflakes for the tops of 
the mountains Tuesday night. 


&& 


Long term /Wednesday through Sunday/... 
weak surface ridge pushes in Wednesday...guidance holds onto boundary layer 
moisture or p-cloudy conds Wednesday. Temperatures should rebound into the 50s 
northwest/60 across the southeast County warning forecast area. Oper solutions advertise a weak wave 
sliding across the Southern Plains Thursday...growing confidence in 
this scenario. 


An item to note is the developing high latitude block across the 
Atlantic begins to influence Greenland...which ultimately will allow 
the departing shortwave Tuesday to retrograde into Quebec and merge 
with a strengthening Hudson Bay vortex thur/Fri. This will play a 
role in the late periods of the extended Friday/Sat/sun in suggesting 
a return to sub-seasonal temperatures. Afternoon temperatures should be warm enough in 
those later periods to limit any precipitation to rain...can/T rule out 
some wet snow mixed in the nocturnal timeframe. 


&& 


Aviation /12z Monday through Friday/... 
conds will continue to deteriorate over the next couple of hours as 
scattered showers become more numerous and ceilings lower. Widespread 
IFR ceilings...with IFR to borderline MVFR visibilities will persist into 
Tuesday as the center of low pressure and its associated fronts 
tracks NE up the Ohio River valley and move right across central 
PA. 




Outlook... 
Monday...rain/IFR ceilings with MVFR to IFR visibilities. Scattered thunderstorms possible 
S/central Penn and the Laurel Highlands of southwestern Penn Monday 
afternoon and night. 


Tuesday...shra/IFR ceilings possible. 


Wed-Thu...no sig weather expected. 


Friday...MVFR ceilings and visibilities possible as weak low pressure tracks 
east from the Ohio Valley...and moves just south of Penn. 


&& 


Ctp watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...dangelo 
near term...dangelo 
short term...dangelo 
long term...beachler 
aviation...Lambert/gartner