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FXUS61 KCTP 141025

Area Forecast Discussion
National Weather Service State College PA
525 AM EST Sat Dec 14 2019

A potent shortwave will lift northeast across Pennsylvania
today, as the associated surface low tracks northward across 
upstate New York. An area of low pressure originating over the 
southern plains will track northeast into the Mid Atlantic 
region late Monday and early Tuesday. 


Dry slot has worked into eastern Pa this morning with little 
more than patchy drizzle falling across much of the forecast 
area at 10Z. However, potent shortwave lifting northeast from 
the Ohio Valley will spread rain back into the region later 

Model soundings become cold enough for a transition from rain 
to snow over the Allegheny Plateau this afternoon. Latest 
HREFV2 indicates a brief period of heavy snow is possible over 
the northwest mountains between 19Z-21Z in association with 
strong forcing ahead of upper trough axis. Will have to monitor 
this area for a possible short-fused advisory. However, marginal
surface temperatures will likely limit accumulations, especially
in valley locations. NBM data suggests spotty advisory level 
snow accumulations are likely on the ridgetops of Warren/Mckean/Potter
counties. However, countywide averages are likely to remain 
below advisory criteria.

As shortwave lifts north of the region this evening, expect snow
to diminish this evening over the Allegheny Plateau, and rain
showers to taper off elsewhere. A tightening gradient in wake of
intensifying low over upstate NY will result in increasingly
gusty west winds across the entire forecast area tonight. Bufkit
soundings indicate there will be frequent gusts to near 30kts. 

Downsloping subsidence should bring partial clearing tonight
east of the mountains. Over the Allegheny Plateau, orographic
forcing will keep clouds and scattered snow showers in the
forecast. Additional snow accumulations tonight should be
generally be an inch or less. 


Sunday should be a blustery day, as region will remain under the
influence of intense storm system lifting into Quebec. Model
soundings support gusts around 30kts through much of the day. 

Approach of high pressure and lowering inversion heights should
cause lake enhanced, orographic snow showers/flurries over the 
western mountains to gradually diminish Sunday. Any additional 
accumulation will be less than an inch. Subsidence to the lee of
the Appalachians should result in a decent amount of sunshine 
Sunday across the eastern half of the state. 

Mixing down model 850 temps between -10C and -5C yields expected 
max temps from around 30F over the high terrain of western Pa, 
to the low 40s across the Susq Valley. 


The bulk of medium range guidance tracks surface low associated
with southern stream wave along the Mason Dixon Line late Monday
into early Tuesday. NBM thermal profiles support an initial
period of snow, followed by a change to rain over much of
the area. However, temperatures may remain cold enough for a
wintry mix along the northern tier even as waa ramps up Monday
night. Although the surface low is not progged to be very deep,
this system will be drawing copious Gulf of Mexico moisture
northward. All guidance currently supports potential precip
totals of around 1 inch across southern Pa, the bulk of which
should fall as rain. 

The 00Z NAEFS supports below average temperatures and generally
dry weather the second half of the week, as upper trough swings
through the northeast conus. 


IFR cigs and vsbsys have formed across central PA with LIFR at 
most TAF sites. Expect these conditions to continue overnight 
and continue through early Saturday. Light rain, drizzle, mist, 
and fog will all contribute to poor flying conditions. 
Periods of VLIFR in 1/4 miles or less is possible at BFD between
09Z to 12Z. 

Conditions will slowly improve Saturday afternoon after 21Z.
MFVR will continue until around 00Z and improve West to East by


Sat...Rain/low cigs likely, especially early. Rain to snow
western 1/3 Saturday PM. Becoming windy late.

Sun...Gusty west wind. AM low cigs/snow showers possible W Mtns. 

Mon...PM low cigs/wintry mix possible.

Tue...Low cigs NW, improving conditions elsewhere.

Wed...Restrictions likely north/west with snow showers.





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