Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 220612

Area Forecast Discussion
National Weather Service State College PA
212 AM EDT Sat Jul 22 2017

Pennsylvania will be on the northern periphery of a subtropical
ridge passing across the southern states through the weekend.
A few rounds of showers and thunderstorms are expected both
Saturday and Sunday, and some could produce gusty winds, hail
and heavy downpours. Another cold front will push through the
area early next week.


Quasi-stationary front draped across south central Pa early this
morning. SPC 05Z mesoanalysis showing around 1000 j/kg of CAPE
along this boundary over the Laurel Highlands. Thus, will
maintain a slight chance of a shower/storm through dawn across
the Laurels and south central mountains. Satellite loop at 05Z
is showing some valley fog development across the north
mountains, but arrival of cirrus shield will likely limit
coverage of fog later tonight.

Temps on track to bottom out from the low 60s north of the
quasi-stationary front over the northern mountains, to the mid
70s south of the boundary over the Lower Susq Valley.


Large MCS forms upstream overnight and approaches eastern OH in
the pre dawn hours Saturday morning. This feature will be the
main player for potential severe weather on Saturday, as strong
moisture flux and increasing boundary layer convergence point
increase the likelihood of strong to severe storms over PA by
late morning and afternoon.

CAMs differ on timing and strength of MCS evolution ranging from
as early as late morning into my western zones to as late as mid
to late afternoon. Think the former is more likely...given quick
moisture return late tonight and Saturday ahead of the
approaching complex. Severe weather threat will be along and
south of warm front, which is progged to reach to near I-80.
Not much of a severe weather threat over northern Pa, where very
little CAPE progged by latest model data.


A second round of convection is possible Sat night as strong
low level jet and plume of anomalous PWATs works through the
area. Convection associated with this feature could potentially
evolve into another MCS with potential for overnight severe
weather in central PA into Sunday morning.

Favorable scenario for additional severe weather across central
Pa during the daylight hours Sunday as the region will be
within warm sector south of anomalous surface low tracking
eastward along the PA/NY border. Moderate CAPES and moderate
westerly flow aloft, combined with large scale forcing ahead of
approaching upper trough, should support widespread convection
by afternoon.

Some uncertainty continues with regards to timing of upper
trough passage early next week, but additional showers/storms
appear possible. A period of dry and cooler weather appears very
likely by midweek, as upper trough axis finally passes east of
Pa and surface high builds into the area.


Quiet night tonight, with most locales remaining VFR, though the
usual spiderweb of valley fog will settle into the western and
northern mtns. The warm air and high dewpoints will allow for
fog formation early, which will mean IFC cigs will form between
04Z to 08Z. Expect them to continue until 12Z to 13Z. Mainly
partly sunny skies with increasing clouds through the day with
CIGS dropping to MVFR between 18Z to 21Z with showers and
thunderstorms in the vicinity of TAF sites after 18Z progressing
west to east as a warm front pushes into the region.
 This will be followed by an upper trough on Sun, which will
keep numerous showers and thunderstorms around over the weekend.


Sat...AM valley fog possible. TSRA/SHRA likely with
intermittent impacts.

Sun...AM valley fog likely. Cig restrictions likely north.
TSRA/SHRA likely with intermittent impacts.

Sun night...Cig restrictions likely. Scattered TSRA/SHRA.

Mon...AM restrictions likely. Scattered TSRA.

Tue-Wed...Patchy AM fog. Otherwise no sig wx.




NEAR TERM...Fitzgerald
SHORT TERM...DeVoir/Fitzgerald
LONG TERM...Fitzgerald/Gartner
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