Saturday, December 16, 2017, 9:30 PM EST
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Area Forecast Discussion
Valid At
Wed, Dec 31, 7:00pm EST
FXUS61 KCTP 162128

Area Forecast Discussion
National Weather Service State College PA
428 PM EST Sat Dec 16 2017

High pressure is moving in for tonight and last into Sunday. A
weakening wave of low pressure will move in from the midwest 
late Sunday. Scattered snow showers will be in store for the 
west during first part of the week. Fast west to east flow aloft
will keep the weather unsettled.


Clouds will likely hold on all night in the NErn half to 1/3rd
of the the area with warm advection and lift just above the
blyr. However, the moisture will be decreasing through the
evening, and the light snow should dwindle to flurries by
midnight and little should be left after that. Mins are tricky
with clearing in the south but the light SW wind will try to
keep temps up a little. Locations to the east of the Susq will
likely fall the hardest with snow on the ground.


Clouds in the NE half/third should begin to break up, but just
in time for a new batch of warm advection to ride in from the 
west later in the day. So, there will likely be an increase in 
clouds over the SW, and a waffle from clouds to no clouds and
back again in the central/NE. We are expecting some light 
precip to break out in the SW/SC counties by nightfall. The
temps will get into the 40s in the south with sun. without much
sun in the NE, it will likely stay below 35F.

The low pressure over the mid-MS valley will fall apart as it
goes into the OH valley and a loss of moisture will kill much of
the precip as the feature fills over us and moves eastward Sun
night. The clouds will likely hang low and thick, keeping temps
up. Many places should stay above freezing.


Fast westerly zonal flow will turn a bit more SW by Friday as a
trough digs over the upper Plains. 

A western trough kicks a strong shortwave out across the Plains
Sunday into Monday. The associated low center will move 
northeast across the Great Lakes staying to our north. This 
system will drag in some warmer air in southwest flow ahead of 
it. However, we may be cold air dammed near the surface so the 
+1 to -2C air at 850 hPa may not translate to a warm boundary 
layer. The warm advection should bring snow and snow to rain in 
the south but QPF amounts are light. Will have to watch for 
potential for some ice also Sunday night. 

Then through much of the week, we move to fast moving pattern 
of weak shortwaves and chances for precipitation (mainly over 
the northern mountains) through the week. As a northern stream 
wave zips by to our north by Monday night, it will bring cold 
air back into the region Tuesday into Wednesday. The northwest 
flow triggers snow in relatively high POPS in NW PA due to LES. 
This cold surge should be relatively fleeting and high pressure 
and a potential surge of relatively warmer air follows Thursday.

The warm advection and approaching cold front will likely 
produce increased potential for snow/ice in the west Thursday 
night into early Friday. As precip works in on Friday, 
precipitation looks to transition through mixed to light rain.
Temps could fall below guidance over the east Thu night if skies
remain clear as exiting surface high pressure will leave a dry
airmass in place.

A strong frontal boundary will likely push another surge of 
cold air into the region Friday into Saturday as the eastern
long wave trough tries to re-establish itself. GFS and ECMWF
diverge by this time, with the EC moving surface low slower and
thus forecasting higher pops than GFS.



Mon...Mainly VFR. Spotty SHSN poss W. 

Tue...Mainly VFR, but possible restrictions in thewestern and 
northern mountains in snow showers.

Wed-Thu...No sig wx.




NEAR TERM...Dangelo
SHORT TERM...Dangelo

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