Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 260045
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
845 PM EDT Thu May 25 2017

.SYNOPSIS...
Mostly cloudy skies with scattered showers and isolated
thunderstorms will persist into the evening hours. A few strong
thunderstorms are possible, mainly across south- central and
southwestern PA. Scattered showers will linger into Friday
followed by a period of mainly dry conditions Friday night into
Saturday. Showers and thunderstorms will likely impact the area
Sunday into Memorial Day. Today will be the coolest day this
week with temperatures rebounding through the holiday weekend.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Back end of double barreled surface low pressure system will
lift north through the area overnight. Sfc cyclonic flow under
cold upper core aloft will support scattered rain showers and
isolated thunderstorms into the early overnight, especially
western sections early this evening. Some areas of heavy rain
this evening will decrease by late evening. Srn third to half
of the CWA remains in a Marginal outlook for severe
thunderstorms through this evening...with local heavy rain
threat being monitored as well through late evening.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
Broad cyclonic/west-northwest flow on southern end of exiting
upper trough will support terrain-enhanced showers on Friday
before precip winds down Friday night/AM Saturday.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
A lower-amplitude but moderately strong westerly (zonal) mid
level flow will set up in the wake of the departing upper trough
with modest height rises/weak will ridging aloft into the
weekend. A warm front is progged to extend east from surface low
in the western Ohio Valley to the mid-Atlantic coast on
Saturday.

Central PA should reside on the north/east fringe of high
instability convective corridor/MCS type pattern expected to
evolve from the central and southern Plains to the southern mid-
Atlantic coast into Saturday night. The greatest risk for
scattered thunderstorms remains over the SW 1/3 of the CWA
which is consistent with previous fcsts. SPC has introduced a
MRGL risk into this area for D3. The remainder of the area
should see a mainly dry start to the holiday weekend but will
maintain slight chance POPs.

The large scale pattern will evolve into a broadly cyclonic
flow regime by Monday with upper trough parked over the Great
Lakes and southeast Canada into midweek. The aforementioned warm
front will lift north across the area on Sunday followed by a
series of weaker cold front associated with shortwave trough
rotating around parent upper low centered to the south of Hudson
Bay. Ensemble blend still supports max POPs on Sunday/Sunday
night into Monday with some additional shower opportunities into
midweek as series of shortwaves rotate around mean upper
trough. Temps should average pretty close to normal/seasonal to
close out the month of May.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...

Meso anal shows 2 surface lows, one over NW PA and another down
over the northern Chesapeake. The water vapor loop shows a
potent shortwave rotating around the parent upper low which is
near the MD/WV panhandles. Modest instability that had
developed over southern areas is now fading with the loss of
heating. There is still some potent shear over the far SE of the
forecast area so the storms rotating up out of MD need to be
watched for the potential of a strong wind gust and/or a
downpour, but the trend will be the severe threat to fade and
the heavy rain threat to shift east as the evening progresses.

A second line of convection has formed and extends from northern
Cambria country down to about Bedford and southward. AOO looks
the most vulnerable over the next hour to see brief
restrictions as these showers and storms move east through the
terminal.

The bigger picture shows most terminals VFR, but with the upper
low expected to pivot over the state during the evening and
overnight, widespread MVFR/IFR can be expected to redevelop.

Cooler air advecting in aloft, combined with deep moisture and
a favorable westerly upslope component over the Western higher
elevations will lead to IFR/LIFR conditions at KJST and KBFD.

Across eastern Pa, light wind, wet ground and light winds could
result in areas of forming late tonight.

After some areas of low cigs and fog early in the day Friday,
the afternoon will feature mainly VFR with brief MVFR/IFR in
isolated-scattered showers...mainly after 16Z. Moist WNW upslope
flow will continue across the western mountains with the best
potential for lingering reduced conditions and scattered
showers.

.OUTLOOK...

Sat...AM fog possible BFD.

Sun...Showers/reduced cigs possible, esp Sun night.

Mon and Tue...AM low cigs poss west. Sct PM tsra impacts poss
east.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Gartner
NEAR TERM...DeVoir/Gartner
SHORT TERM...Steinbugl
LONG TERM...RXR/Steinbugl
AVIATION...La Corte


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