-- Discussion containing changed information from previous version are highlighted. --
266
FXUS61 KCTP 270605
AFDCTP

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

.SYNOPSIS...
A warm front will lift northeast into the state tonight, but
will likely stall its progress near or just to the east of the
Susquehanna Valley until later Monday.

Low pressure will pass over the Upper Great Lakes on Memorial
Day, dragging a cold front through late Monday/evening. An upper
level trough will build into the region for the remaining
portion of the week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
The focus this evening is on an approaching band of strong to
severe thunderstorms entering Southwest PA at the nose of a
strong southwesterly low level jet. Latest HRRR, which should
perform well in a strongly forced scenario as this, tracks the
band of convection northeast across the entire forecast area
between 00Z and 06Z. However, it will be running into a much
less unstable environment, so anticipate a diminishing severe
weather threat. The best chance of severe weather should be over
Somerset County, where the 22Z SPC mesoanalysis shows capes in
the 500-1000J/kg range. RAP 0-3km shear vectors are around 30kt
and perpendicular to the convection, so can`t totally rule out a
brief QLCS tornado in the vicinity of Somerset Co, but the
greater threat is to the west of our area.

The band of showers and embedded tsra should lift north and east
of the forecast area by about 08Z tonight, as the associated
shortwave/low level jet lift into NY State. Generally rain-
free weather is expected during the pre-dawn hours with breaks
in the overcast. However, model guidance indicates an upsloping
southeast flow will yield developing stratus across the higher
terrain of Northern and Eastern PA.

Surging low level moisture and cloud cover should result in a
significantly warmer night than those recently, with min temps
in the 60s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/...
Falling heights and surging pwats ahead of the next shortwave
lifting out of the Ohio Valley will spread numerous showers and
embedded tsra into the region later Monday morning. Initially,
low clouds and rainfall should hold temps and the severe wx
threat in check. However, breaks in the overcast/modest diurnal
heating, combined with favorable shear profiles, support
organized convection and a threat of severe weather during the
afternoon to early evening hours. The best chance of supercells
and an isolated tornado appears focused over the Susq Valley,
where low LCLs are anticipated and updraft helicity values from
at least one HREF member tops 150m2/s/2.

The most impressive pwats are progged to have shifted east of
the area during peak instability of the PM hours, so think any
flash flooding will be isolated at best. Ensemble mean qpf
between 0.25 and 0.50 inches appears the most likely rainfall
Monday for most of the area. However, HREF output supports
isolated totals near 2 inches associated with stronger tsra.

A seasonably strong surface low will track west of PA through
the Great Lakes Monday, dragging a trailing cold front through
the area Monday evening. The threat of showers/tsra will end
over most of Central PA with the passage of the front. However,
low level instability associated with a deepening trough over
the Grt Lks could result in late night showers over the NW Mtns.

&&

.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 /06Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
A line of SHRA continues moving across central PA early this
morning with generally VFR/MVFR conds. Some drops towards IFR in
the heaviest showers remain possible across E PA with locally
gusty winds at IPT in the next hour or two. Some uncertainty in
how low vsbys/cigs get overnight but generally expect VFR/MVFR
to continue with a light breeze overnight. LLWS appears likely
in the overnight across much of central PA, especially W PA into
sunrise hours.

Guidance continues to suggest IFR-to-MVFR cigs will continue
through much of Monday across E PA. Scattered TSRA are expected
to form in the afternoon and evening, perhaps forming into a
line of convection. Some of the strongest storms (especially
across E PA) could bring about localized gusty winds and an hour
of more restrictive conditions, but confidence remains too low
to include in this TAF package. Cigs will trend higher late in
the day outside of thunderstorms as drier air works in from the
west.

Outlook...

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

Thu-Fri...Predominantly VFR.
-- End Changed Discussion --

&&

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

&&

$$

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