Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
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FXUS61 KCTP 212050
Area Forecast Discussion
National Weather Service State College PA
350 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/...
Dense fog has largely dissipated but still plenty of low clouds
and 1-3SM visibility in the central and southeast valleys. Have
adjusted max T down a few degrees in these areas which will not
see the sun today. On the flip side, a spring-like day can be
found along and west of the Allegheny Front with 55-65 degree
readings over the western 1/3 of PA. Even a few cu noted on the
vis sat now being overrun by increasing high clouds from the SW.
Latest thinking is that low clouds and fog will expand/redevelop
tonight into Sunday morning particularly from the central ridge
and valley region into the Susq. valley. Later shifts may need
to issue another dense fog advisory. 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.
.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 /20Z SATURDAY THROUGH THURSDAY/...
VFR over the western 1/3 this aftn and eve should trend toward
MVFR tonight with IFR possible at KBFD. Vis satellite and obs
trends indicate some improvement in cigs/vis over the central
and eastern TAFs. However, expect widespread IFR-LIFR conditions
to continue/redevelop overnight with local cigs/vis AOB airfield
mins into Sunday morning.
Sun...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.