Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 220224

Area Forecast Discussion
National Weather Service State College PA
1024 PM EDT Fri Jul 21 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.


A boundary dropping southward through PIT is firing off
convection. Dewpoints on one side are in the m60s, and KPIT is
76F. Don`t see that too often in PA. Some of this convection
could slide into the Laurels shortly, but HRRR & RAP - which, to
their credit, do have it there - die it off. Have just mentioned
a shower there through 2-3AM. Dewpoints are high, sky only
partly cloudy, and the air is calm. Fog already in fcst for some
places, and have added fog to the rest of the area, mainly in
the valleys. All the rest of the forecast is in great shape. It
was a dark and muggy night...

Convection all but dead. Just a hint of taller cu in the far srn
tier, and the 20 POPs there will expire in an hour or so - right
on time. Other than the high clouds in the N, clearing should
come to much of the area shortly.

Weakening MCS traversing WV and approaching the WV and MD
panhandles at mid afternoon. PW pooling around 2" along the
Mason Dixon line and slowly lifting northward should bring
isolated to scattered coverage of showers and thunderstorms
through this evening across my southern tier counties (Laurel
Highlands and South Central Mountains), with mainly dry
conditions expected elsewhere.

remnants of aforementioned MCS track off the mid Atlantic
coastline later this evening, and any diurnally-driven
showers or storms along the southern tier should die out around
sunset. Weak surface ridge passes over PA tonight bringing fair
weather and mins ranging from the upper 50s north to around 70


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. Warm front pushing into the region on
Saturday will also tend to favor lower LCLs and sufficient shear
for rotating updrafts. Farther north, extensive cloud cover
associated with the warm front will likely result in limited
CAPE Saturday as the 00Z GEFS shows.


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...Dangelo/DeVoir
LONG TERM...Fitzgerald/Gartner
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