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NWS State College, PA Forecast Discussion

FXUS61 KCTP 261849

Area Forecast Discussion
National Weather Service State College PA
249 PM EDT Mon Jul 26 2021

Weak high pressure will maintain control through early Tuesday,
with rain free conditions. An upper level disturbance will bring
scattered showers and thunderstorms to the northern tier late
Tuesday into Tuesday evening, with isolated showers and
thunderstorms dotting the region again on Wednesday.


215 pm update... As expected, drier air has mixed down to the
boundary layer this afternoon, keeping the vast majority of the
convection south of the Mason-Dixon line.

Tonight should end up mainly clear, with patchy valley fog again
late at night over the northern tier and along the Allegheny
front. Lows by daybreak will range from the mid 50s over the
northern mountains, to the mid-upper 60s over most of the
Susquehanna Valley.


230 pm update... After a sunny start to the day Tuesday, model
guidance is pointing to the development of scattered afternoon
and early evening showers and thunderstorms up over the northern
tier (generally north of I-80), as the latest in a series of
northern stream short-waves dips into the northeastern U.S.
Although the overall instability profile looks marginal (ML
CAPE of 500-1500 j/kg), deep-layered shear should be increasing
ahead of the short-wave, with increasing low-level lapse rate
and DCAPE values as well. Thus, there appears to be a low end
threat for downburst producing storms for the northern tier.

It will be a very warm afternoon again, with highs ranging from
the 80s over much of central PA, to the lower 90s in some of the
southern and eastern valleys.

Residual evening convection should diminish with time Tuesday
night, with lows by daybreak ranging in the 60s.

As the core of the above mentioned short-wave exits on
Wednesday, large-scale forced ascent seems muted. However, with
a cyclonic flow pattern aloft still in place and a similarly
warm air mass, we`ve kept the mention of isolated showers and
thunderstorms in the forecast.


Overnight convection (late Wednesday night) in the Great Lakes
region should fade as it approaches Lake Erie by early Thursday
morning. This activity may influence storm chances and severe
risk on Thursday/D4.

A cold front is forecast to move southeastward across the lower
Great Lakes on Thursday. Instability should develop along and
ahead of the front Thursday afternoon with isolated severe
thunderstorm development possible across central Pennsylvania.
It is conceivable that SPC may introduce a categorical risk or
threat area with the new D3 outlook. PWs > 1.5 inches also
favors potential for locally heavy downpours. While the
progressive nature of storms will likely be a limiting factor,
much of the area has observed well above normal precip over the
past few weeks making soils more susceptible to flooding. We
would not be surprised to see a WPC D3 MRGL ERO by this time

The weather pattern from Friday through Sunday favors mainly
dry conditions as multiple shortwaves dig downstream from
western US ridge and help to carve out a mean upper trough over
the Midwest/Northeast. A weakening frontal boundary will bring a
low chance of showers and t-storms on Sunday. Below normal PWs
are a persistent feature with high pressure setting up some cool
nights and comfortable days heading into the first week of

The CTP medium range forecast grids did not deviate much from
NBM for this cycle with limited targets of opportunity.


VFR flying over just about the entire region. Some convection
across PA/MD border will move into MD by 20Z.


Tue...Patchy AM valley fog then isolated SHRA Northern Tier.

Wed...Mainly VFR. Isolated SHRA/TSRA possible.

Thu...Isolated PM TSRA impacts possible.

Fri...No sig wx expected.


It`s been a wet July in some parts of central PA. Through July
25th, the monthly precipitation at Harrisburg is 7.99 inches
which currently ranks 2021 as the 9th wettest July on record.




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

NWS CTP Office Area Forecast Discussion

Courtesy of the National Weather Service forecast office State College, Pennsylvania

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