Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 251617

Area Forecast Discussion
National Weather Service State College PA
1217 PM EDT Thu May 25 2017

The soaking rain earlier this morning will be showery through
this afternoon, with a few strong thunderstorms 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.


10Z: Band of heavier rain focusing over the western 1/2 of the
CWA early this morning. Highest rainfall totals in the past 12
hours are concentrated over this area with max rainfall amounts
around 1 inch over parts of the Laurel Highlands.

Previous: All near term HIRES guidance shows steady light to
moderate rain overspreading Central PA through 12z. Peak
rainfall intensity between 09 and 15z still looks good
coincident with max H85 mflux anoms and strong SE LLJ. Multi-
model derived QPF amounts between 0.50 and 1 inches expected
through midday with areas of 1"+ amounts in the southern
Alleghenies aided by orographics and robust dynamics. Negligible
instability will inhibit short-term rain rates resulting in a
soaking rain with no runoff issues anticipated. The steadier
rain should lift over the northern 1/2 of the area later this
morning with overall mode of precipitation becoming more showery
this afternoon with partial sunshine/cloud breaks expected in-
and- out of shower spells.

Occluded front pushes north of the Mason-Dixon line this
afternoon which should allow for at least modest destablization
with cloud breaks most likely across south-central PA. SPC has
expanded MRGL risk northward into this area with thinking that
thunderstorm development will concentrate near the frontal
boundary over south-central PA. Instability is not that great
but shear profiles are supportive of at least low risk severe
probs. There is also plenty of large scale forcing to work with
given strong height falls/negative tilt trough and favorable
left-exit region jet dynamics. Will include risk for isolated
strong/severe storms in HWO. Anticipate a gradual decrease in
shower activity tonight into early Friday morning with consensus
max POPs focused over the far NE and SW portions of the CWA.


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. 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 1/4 to 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.


Primary surface low pressure located over Ohio will rotate a few
disturbances northeast across Pennsylvania this afternoon and
evening with rounds of showers (and isolated-sct TSRA across the
SW third-half of the state after 19Z).

Widespread IFR/low MVFR cigs will continue across Central Pa and
the Susq Valley through the mid afternoon, with gradual
improvement across at least the western TAF sites as an
Occluded front lifts NE across that region with some drier air
aloft in its wake along with a gradual veering of the wind to
the southwest, then west at KJST,KAOO KUNV and KBFD late this
afternoon and this evening.

The drying aloft, and some breaks in the dual-multi layered
cloud deck, will help to create some MDT instability for the
chc of a TSRA. Mentioned VCTS at both KJST and KAOO, and may
need to include it at KUNV in the 18Z TAF package.

MVFR to IFR cigs will likely linger in many locations tonight
with vsbys dipping back to MVFR at most TAF sites.

Cooler air advecting in aloft, combined with deep moisture and
a favorable westerly upslope component over the Western Mtns
and Laurel Highlands will lead to periods of LIFR/VLIFR cigs and
IFR to ocnl LIFR vsbys at KJST and KBFD.

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


Fri...AM low cigs/showers likely BFD/JST.

Sat...AM fog possible BFD.

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

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




NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Steinbugl
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