050
FXUS61 KCTP 071904
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
304 PM EDT Tue May 7 2024

.SYNOPSIS...
A warm front over Southwestern and South-central Pennsylvania
this afternoon will drift slowly to the northeast late today
and tonight while an area of low pressure along the front
passes north of the state early Wednesday.

Another, more significant, wave of low pressure will pass south
of PA Thursday.

An upper level trough will then pivot into the region late this
week into next weekend, cooling things down a bit with
temperatures near to slightly below normal.

&&

.NEAR TERM /THROUGH TONIGHT/...
Slow moving frontal boundary extended from near KBFD to KUNV and
KMDT at 1830Z and will continue to drift north through the rest
of today and early tonight.

RAP and analyzed sfc-based CAPE to the south of the aforementioned
front was between 500-1000 J/KG, but shouldn`t increase much
for the remainder of this afternoon as another deg or two C of
warming aloft and meager mid level lapse rates advect east over
the CWA. Expect just sparse, mainly isolated coverage/POPS for
showers across the southern third of PA late this afternoon and
evening where CAPE values were highest - around 1000 J/KG

Plenty of sunshine will persist across the northeastern half of
PA while variable amounts of dual layered cu and alto cu or
cirrus clouds occur near and to the southwest of the front.

Temps through the rest of today will be unusually uniform from
the higher terrain of northern PA to the typically warmer
valleys in Southern PA, with highs in the low to mid 70s and
roughly a 5 deg F or less spread. The temps will be 4-9F above
normal with the greatest departures seen over the northern tier
with much more sun there than in the South.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
Low pressure will move toward PA and wrn NY this evening,
crossing the area overnight. PWAT values will climb to between
1.2-1.6 inches 9+1-2 sigma) and CAPE will increase through the
middle of the night and numerous SHRA/TSRA are expected with the
greatest coverage and intensities over the W during the late
evening into the middle of the night as the nose of a moderately
strong, 35-45 KT LLJ approaches and aids in enhancing mesoscale
UVVEL in the warm sector.

Intense/near-severe storms shouldn`t get much farther east than
a BFD-UNV-AOO line. SPC has the SWrn corner of the CWA into the
MRGL risk for svr wx as a cold front plows thru late
tonight/early Wed. The period of showers and a few TSRA will
peak between about midnight and 5 AM across Central and Eastern
parts of the CWA.

Tonight should be very warm for early May due to the clouds and
mild southerly flow before the cold front passes later at night.
Mins in the L60s will cover most of the CWA.

Model guidance tracks the weak surface low north of PA Wednesday,
with a weak trailing cold front coming through during the morning
hours. Any morning showers should give way to increasing sunshine,
as drier air works in behind the front. Model 850mb temps near
15C support highs ranging from the mid and upper 70s over the N
Mtns, to the low and mid 80s in the valleys of Central/Southern
PA. Mixed in lower PWATs via the NBM 25 pctl values for Wed
afternoon as sfc dewpoints dive into the 40s (and possibly a few
u30s across the Northern Mtns).

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Unsettled weather will return Thursday, as an upstream trough
approaches from the Grt Lks. Latest guidance tracks the associated
surface low south of PA, resulting in a rainy/cool Thursday, with
elevated convection and a marginal risk of severe wx along the
southern tier counties. Will likely be undercutting NBM temp
guidance Thursday if current model trends hold. Raw operational
model surface temps struggle to reach 60F over parts of the
area Thursday. Latest ensemble plumes indicate most likely rain
totals Thursday of around a half inch.

A notable trend toward cooler conditions for late this week
through the coming weekend as a broad trough develops over the
Glakes and Eastern U.S. with several smaller scale shortwaves
moving southeast within the northern branch of the upper jet.

The surface low and deepest moisture is progged to shift east
of the area Thursday night. However, falling heights ahead of
the positive tilt upper trough (and cold 700 mb temps falling to
around -4C) will likely support scattered-numerous, mainly
diurnal showers Friday through Sunday. A low-topped tsra cannot
be ruled out Friday afternoon/early evening.

GEFS mean 850 mb temps slip to between +2 and +4C (or about -1
sigma) Friday night through Saturday, before rebounding a few
deg C Sunday into Monday. Mean 925 mb temps of just 8-10C later
Friday through Sat morning will likely top even cooler LLVL air
under cloudy conditions.

This cool airmass (with Canadian origin and trajectory over
Lake Erie waters still in the upper 40s to around 50F) will
combine with numerous late morning through early evening showers
across at least the Central and Northern part of the CWA Friday
to likely yield the coolest day we`ll see til this Autumn with
high temps staying in the U40s in some spots across the Northern
Mtns. Highs in the mid 50s to mid 60s will be common heading
southeast from the Allegheny Front.

Temps will still be 2-5 deg F below normal over the upcoming
weekend with mins at night near to a few deg F above normal due
to varying amounts of clouds and at least a light breeze, which
should limit any potential for frost to the patchy variety and
confine it to the Northern Mountains Sat, Sun and Mon mornings.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
Most or all of central PA will see VFR conds continuing through
early tonight with just some spotty, brief MVFR conditions in
isolated SHRA.

A warm front extending from KBFD to KUNV and KMDT at 1830Z will
lift northeast across the remainder of the region late
today/tonight. A potent upper level disturbance and sfc cold
front will push east from the Ohio Valley later tonight and
early Wed, preceded by a 4-6 hour period of LLWS late tonight
and early Wed morning. This southwesterly low level jet causing
the wind shear will also aid in the development of numerous
showers and a few thunderstorms and a higher frequency of MVFR
and brief IFR conditions, especially after 04z Wed.

Drier air will begin to work into the western airfields around
12z Wed, but sfc fog may develop prior to sunrise as the low
level moisture is slow to scour out.

Outlook...

Tue...AM low cigs/showers possible southern tier of PA.
Scattered evening tsra impacts possible W Mtns.

Wed...AM low cigs/tsra possible.

Thu...Periods of rain/low cigs likely. Scattered afternoon
TSRA.

Fri and Sat...Showers with periods of low cigs possible.

&&

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

&&

$$

SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert
LONG TERM...Martin
AVIATION...Lambert