Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
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FXUS61 KCTP 212220
Area Forecast Discussion
National Weather Service State College PA
520 PM EST Sat Jan 21 2017
Unseasonably mild weather will continue through the weekend.
A complex and dynamic storm system will bring the potential for
heavy rain, accumulating snow and strong winds to portions of
Central PA on Monday. The mild conditions will last into the
middle of next week before a pattern change brings colder air
and more seasonable temperatures to close out the month.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
-- Changed Discussion --Fog rapidly lowering/redeveloping this evening in areas where
inversion hung strong throughout the day. Already seeing M1/4sm
visibility pockets and the next few hours should see many more
with some very difficult travel at a time of day that usually
does not see dense fog. Issued Dense Fog Advisory for all most
areas east of the Allegheny Front until 03z...as mid to high
clouds spreading ENE with approaching upper trof should diminish
the extent and severity of fog by late evening...we think.
Otherwise, cloudy and unseasonably mild overnight with minimum
temperatures +20-30 degrees above normal for late January. There
could be some pockets of light rain/drizzle but generally kept
POPs below 20 percent. Rainfall associated with surface low
tracking northeast from GA/AL is fcst by the models to stay
southeast of the area.
-- End Changed Discussion --
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Closed mid-level low tracks from the ARKLATEX to western VA/NC
by 23/12z. Moisture and inflow will increase ahead of the mid-
level system and should support rainfall pivoting northward into
southern areas by the end of the period. Model QPFs indicate
the main rain axis stays to the south of the PA/MD line although
placement highly anomalous easterly flow of high PW air into e-w
frontal zone has me a bit concerned. One thing of note is an
increase in winds over the Lower Susq. valley with gusts over 40
mph possible by daybreak Monday. Temperatures stay very mild
and well-above normal for this time of year.
.LONG TERM /MONDAY THROUGH SATURDAY/...
All model data tracking closed upper low northeast across
Virginia Monday. Continue to maintain 100 pct POPs across the
entire region, given the strong upper lvl divergence, anomalous
easterly low lvl jet and associated PWATS. Latest GEFS/SREF
also both support the 100 POP forecast. Initially, model temp
profiles are warm enough everywhere for rain, but dynamic
cooling associated with the strongest forcing will likely
support a change to snow, at least temporarily, over the higher
terrain of central Pa. GEFS/SREF ptypes still strongly favor
rain, but based on operational model soundings and colder 12Z
ECMWF will maintain mention of snow over the central counties.
Best chance of accumulating snow based on soundings is across
the northern Mtns, where a few inches of accum appear probable
by Mon evening. Uncertainty too high to mention accums further
south, but the potential for a few inches of wet snow remains
from the Laurel Highlands into the Central Mtns.
Another area of concern is the potential for flooding. Target
area for the heaviest rain is across the south central part of
the state, where orographic forcing at nose of powerful easterly low
lvl jet will play a role. Mean QPF from both SREF and GEFS max
out around 1.5 inches in this region, while FFG/FFH is around 2
inches. However, locally higher amounts seem probable and are
hinted at by the higher resolution NAM, so will mention the
possibility of minor flooding in the HWO for this area late
Lastly, Bufkit soundings indicate wgusts in excess of 40kts are
possible across southeast Pa, as low lvl jet swings through
Monday. Per coordination with LWX/PHI, will hold off on an
advisory pending increased confidence from later models.
Precip will lift out of the region Monday night, as sfc low
passes off the NJ coast. Upper ridging will build into the
region later Tuesday into early Wed, bringing fair and mild wx.
A shortwave passing across the eastern Grt Lks will push a cold
front thru Pa late Wednesday, accompanied by sct showers, then a
shift toward colder wx is progged by all med range guidance for
the Thu-Sat time frame, as a deepening upper lvl trough forms
over eastern North America. Best chance of precip will be in the
form of lake effect snow showers across the NW Mtns during this
time, with dry weather likely elsewhere.
.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
Widespread IFR-LIFR over much of central and eastern airfields
early this evening. Areas in the western mountains have mixed
into the warm air, and are VFR with scattered to clear skies.
Expect IFR-LIFR conditions to persist/expand over the next
several hours. Approaching shortwave may bring a slight
improvement to conditions after 03z...but generally a low
cig/vsby night in store for most of the region.
Sun...IFR-LIFR early, some slight improvement to MVFR/IFR. Rain
spreads south-north into Sunday night.
Mon...Rain/low CIGs likely.
Tue...AM rain/snow and low CIGs possible.
Wed...Reduced CIGs/showers possible NW.
Thu...MVFR/IFR in rain/snow showers mainly west.
-- Changed Discussion --Dense Fog Advisory until 10 PM EST this evening for PAZ012-018-
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