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284
FXUS61 KCTP 271502
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1102 AM EDT Mon May 27 2024

.SYNOPSIS...
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Severe weather is likely today, mainly over the eastern half of
the state as a low pressure area passes over the Upper Great
Lakes and drags a cold front through by late evening. An upper
level trough will build into the region for the remaining
portion of the week. Occasional showers and a few thunderstorms
are expected Tuesday and Wednesday. The week will end dry and
the dry forecast should last through Sunday.
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&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...
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Widespread cloud cover so far has limited significant
destabilization of the warm and moist airmass across the region
with the warm sector.

First round of convection (almost exclusively in the form of
SHRA) late this morning covered the central third of the state
and will gradually deepen into embedded low topped TSRA early
this afternoon across the Central Mtns and Susq Valley where the
best LLVL theta-E convergence, 0-1 KM shear and upper level
diffluence will be found.

MU CAPE is nearing 1000 J/KG across much of the Lower Susq
Valley this midday hour with values around 500 J/KG across the
Central and NE Mtns of the state where thicker cloud cover and
showers were prevalent.

SPC SLGT risk area across the Eastern Half of PA looks in good
shape at this point. Some concern about a second line of
convection developing along the cold front across our far
western zones late this afternoon and early this evening, but
that area will be competing with slowly decreasing deep layer
moisture and the loss of deep-layer shear beneath the
unfavorable and departing left entrance region of the
Southwesterly upper level jet.

Previous...

The arrival of the better forcing this afternoon coupled with
the heating/destabilized llvls should put all the threats into
play for much of the area. The organization/storm-mode is rather
a toss-up at this point with many factors giving different
hints. MLCAPE in the 1000-1200 range are not super. WBZ is low-
ish, sitting at or just below 10kft in most places for some part
of their respective unstable period. The progged hodographs for
this aftn are not too compelling, either, but an SPC 5% tornado
risk is a fairly rare thing for PA (a couple times/yr). Will
play up the wording for tornadoes a little more than usual in
the HWO and IDSS briefings.

As the afternoon progresses, the western tier of counties should
get into more-stable air, and by 6-7PM, only the SErn quarter of
the area will still be in their most-unstable period. Sct SHRA
will occur along the real cfront in the evening, but they will
be going over much more stable ground.

Heavy precip is more likely in the east as in the west, as PWATs
reach near 2" in the Lower Susq by noon. But, the storms should
be moving along at 30 MPH. The multiple shots at
thunderstorms/heavy rain, and the wet ground from the rain we`ve
had over the past 12 hrs will be the main reasons for FF threat.
The threat is not high enough at this point to post a FF Watch
for any of our area. The east is where the PWATs do climb high
and where the highest chcs of having 2-3 TSRA in 6-8 hrs lie.
So, that is where WPC has painted the SLGT risk of excessive
rainfall.

Maxes today will hold in the 70s for almost everyone.
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&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM TUESDAY/...
As the cfront moves through in the evening, some drier air comes
in. The wind stays up in the 5-10KT range, so fog may occur, but
won`t put it in the wx grids at this point. Low clouds under the
digging longwave trough will come back into the NW quickly.
There could be a few SHRA there, but these should not push too
far into the CWA, maybe just 3-4 counties overnight. Mins in the
50s and lower 60s are still well above normal.

Upper energy under the trough should spark some SHRA and a few
TSRA on Tuesday. But, daytime temps stay near normal in the SE,
and fall short of normal by 5-6F in the NW. Didn`t want to take
the 30 PoPs any farther SE than an AOO-SEG line for Tuesday, but
isold convection is expected in the SE. In fact, at least one
HREF member pops things along the srn border (S of the lower
clouds) and rides them into the Lower Susq. Thin CAPEs and short
storms will keep the threat of SVR down to very low, if any risk
at all. But, there is high 0-6km shear (40-50KT), generally
before the SHRA/TSRA arrive.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Medium range guidance continues to point to a period of cool
weather Tuesday through Thursday, as a deep upper level trough
pivots southeastward from the Great Lakes. Cold temps aloft
should support diurnally-driven showers/storms Tue and Wed,
with the highest POPs across the elevated heat source of the
Allegheny Plateau. The best overall chance of showers should
come with the passage of a strong shortwave on Wednesday.

PoPs will fall to slight chance on Thursday as drier air moves
in on the back side of the upper trough. This will begin a trend
toward drier and warmer weather Friday into Saturday, as the
upper level trough axis shifts east of PA and high pressure
builds into the region. An approaching frontal system could
bring our next round of showers/storms by next Sunday.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
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An area of slowly intensifying showers with periods of MVFR will
impact KUNV and KIPT through 17-18Z before becoming concentrated
and deepen into an area of heavier rain with embedded TSRA near
and to the east of a KIPT to KSEG and KMDT line.

The best threat for IFR with strong downburst TSRA wind gusts
over 40 KTS will be focused across the Susq Valley and points
east this afternoon.

Over the Central and Western Mtns, a likely period of VFR conds
is expected to occur from about 17-20Z before the next round of
precipitation approaches from Wrn PA along and in advance of a
cold front.

After 20Z, probs of TSRA increase for the western airfields
although there is some uncertainty on the exact extent of where
TSRA will impact airfields. Guidance suggests MVFR restrictions
at this time, but localized IFR restrictions are possible. There
is low confidence on the direct impacts at airfields, so have
left VCTS mentions at this time. Cigs will trend higher later
in the day outside of thunderstorms as drier air works in from
the west with a light breeze continuing into the overnight
hours.

Outlook...

Tue-Wed...Brief restrictions are possible in scattered showers,
but much of the time should be VFR.

Thu-Fri...Predominantly VFR.
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&&

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

&&

$$

SYNOPSIS...Lambert/Dangelo
NEAR TERM...Lambert/Dangelo
SHORT TERM...Lambert/Dangelo
LONG TERM...Evanego/Colbert
AVIATION...Lambert/NPB