FXUS61 KCTP 240118

Area Forecast Discussion
National Weather Service State College PA
918 PM EDT Tue Oct 23 2018

A cold front will push east of the region by evening, delivering
windy and colder conditions. Scattered rain showers will change
to snow showers over the north this evening with a coating to an
inch of snow possible on the Northwest Mountain ridgetops later
tonight into Wednesday. Well below normal temperatures will
follow for Wednesday and Thursday, but will be softened on
Thursday by diminishing northwest wind as a large area of high
pressure slides southeast across the state. Fair conditions will
last into Friday, but unsettled conditions are expected by late
Friday as moisture returns. A soaking rain is likely Saturday
afternoon into Sunday.


Earlier rain showers generally north of Interstate 80 have
diminished to just isolated activity near the New York border.
Colder air will continue to work into the region, causing these
rain showers to mix with and change to snow showers. Still
think snow accumulations would max out on the order of an inch
over my lake effect northwest zones. 850 mb temps near -4 to -6C
overnight into Wednesday.

Winds will remain breezy overnight but lower than the 25 to 30
mph gusts of earlier today. Mins will range from near 30 across
the northwest to the upper 30s southeast.


Cold advection persists on brisk northwest winds on Wednesday
and additional scattered snow showers and flurries are expected
across the north, with perhaps scattered rain or snow shower
extending to the I80 corridor, but most will remain dry.
Considering the rather low subsidence inversion base of just
4-5 kft agl, the stratocu clouds will be mild and capable of
producing only spotty light rain/snow showers at most. Max temps
Wed will be between 50-53F across the Susquehanna valley and
just upper 30s to Low 40s across the higher terrain of the
Allegheny Plateau.


The extended will start off dry with the fair cool weather
lasting through Thursday into at least the first half of Friday.

Models continue to converge on some sort of east coast
cyclogenesis as the energy from still potent eastern Pacific
Hurricane Willa hops across Mexico and become involved with a
baroclinic zone over the northern Gulf of Mexico.

At least through the 84 hour timeframe, the 12Z NAM is faster
with the low and precip overspreading the region. The ECMWF and
Canadian are very similar from that point through about mid day
Saturday showing a surface low tracking up the Del Marva coast.
The GFS is the outlier being slower and more inland with a low
moving near Lancaster County, but not until 12Z Sunday. The GEFS
surface low is not as slow as the 12Z deterministic position,
but it is still slower than the EC and Can models.

I leaned closer to the two faster models showing a cold rain
overspreading the area Friday night and lasting through Saturday
morning, before becoming more showery in the afternoon. There's
still a chance for some wet snow over the higher elevations.
Plume forecasts show the area from Johnstown up and through the
northern mountains with about 30-50% of the members having snow
in them with mainly rain for the rest of the sample stations.
Overall I went a little higher than blended MOS POPs. As far as
snow, this time of year, snow is usually highly dependent on
elevation, time of day or night as well as precipitation rates
and so far this scenario doesn't look to deviate from that

After the main low passes NE of the area during the day Sunday,
the EC and Canadian models bring another chunk of shortwave
energy aloft through the forecast area Sunday night into Monday
morning. If the scenario plays out, that could actually be the
first coating of snow for many locations. The GFS is
significantly slower on this secondary shortwave, about 24 hours
slower in fact.

Overall the extended will see temperatures averaging well below
normal right into early next week.


A tight gradient between low pressure over southern New England
and high pressure over the Grt Lks will result in a breezy night
across central Pa with northwest winds close to 10kts. Moisture
flowing off of the Grt Lks is likely to result in mvfr cigs
across the high terrain of the Alleghenies from KBFD south
through KJST later tonight. Elsewhere, model soundings support a
high confidence of vfr conditions across southeast Pa and
likely vfr in the ridge/valley region from KAOO to KUNV.

Gusty northwest winds will be the main issue Wednesday. After a
late night lull in the winds, stronger flow aloft will begin
mixing to ground level by late morning and will last through
early Wednesday evening. Model soundings support gusts in the
15-25kt range, with the highest gusts across southeast Pa in
vicinity of KMDT/KLNS. SREF/HREF probability charts suggest MVFR
cigs over the Laurel Highlands will lift to vfr by afternoon.
However, they are likely to persist for most of the day across
the northwest mountains (KBFD).


Thu...AM valley fog possible western Pa.

Fri...Evening rain/low cigs possible, especially south.

Sat...Rain/low cigs possible.

Sun...Rain/low cigs possible, especially early.




NEAR TERM...DeVoir/Tyburski
LONG TERM...La Corte/Lambert
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