179
FXUS61 KCTP 260856
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
456 AM EDT Wed Jun 26 2024

.SYNOPSIS...
A cold front will drift southeast across the Lower Great Lakes
late today and push across Pennsylvania tonight.

This front and the deep, rich moisture ahead of it will spark
numerous showers and scattered thunderstorms, some of which
could produce gusty to localized damaging wind gusts and heavy
rain.

High pressure will build into the region for Thursday and
Friday. A relatively zonal flow will remain in place through
early next week, with a cold front passage either late Saturday
or early Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...

Variable amounts of mainly cirrus and some alto cu (along with a
few areas of stratocu across the NW Mtns) and a light
southwesterly breeze helped to keep temps notably warmer than
Monday night/early Tuesday. Daybreak temps were in a fairly
tight range from the mid 60s to low 70s.

A cold front stretched from Northern Lower Michigan to near
Chicago at sunrise will push southeast and cross the
Commonwealth later tonight and early Thursday.

Preceding this front, a moderately strong southwesterly flow
in the low to mid levels of the atmosphere will transport
abundant moisture into the state. There will be more clouds
than sunshine today and afternoon highs ranging from near 80
across the highest terrain of the north and west, to the low
and mid 90s in the valleys of South-central and Southeastern
PA will be about 5 degrees above normal across the Alleghenies
and 8 to 10 degrees above normal elsewhere.

Weak jet forcing, the lack of a significant llvl boundary and a
fairly strong mid level cap (7.5 to 8.5 C at 700 mb) with
another isothermal layer between 500-400 MB.

Diurnal heating of an increasingly moist/unstable airmass,
combined with falling heights ahead of the upstream trough, will
result in developing convection later this afternoon.

Broader scale, deeper lift and cooling/increasing shear aloft
that will help to accentuate shower and thunderstorm development
won`t arrive until late this afternoon and tonight.

This will be the period of greatest areal coverage and
intensity of the thunderstorms that could bring locally over one
inch of rain in just a 20-30 minute period, and even
potentially higher amounts where separate storm cells train
over the same location.

NAM is the most juiced with respect to 0-1 KM EHI values, which
peak in the 1.5 to 2.5 M2/S2 across the Lower-Mid Susq Valley
around 00Z Thur. Although SPC did remove their 2 percent TOR
risk within the Broader SLGT risk area covering most of PA, the
timing and degree of LLVL shear ahead of a potential MCV moving
across the Ncent Mtns and Susq`s West Branch could lead to some
transient supercell structure across the eastern 1/3 to 1/2 of
the CWA in the 22Z Wed - 02Z Thu period.

Convection will weaken and decrease in coverage from northwest
to southeast later tonight, as the upper trough and associated
cold front works through the CWA. Lows tonight will vary from
the mid 50s over the NW Mtns to near 70F in the larger Metro
Areas of Scent and SE PA.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Large scale subsidence and the arrival of much drier air behind
the exiting cold front will lead to fair and seasonable
conditions Thursday. Surface high pressure building over the
region should result in fair and cool weather Thu night. Fair
and slightly warmer conditions are likely Friday, as low pwats
persist over PA and a return southerly flow develops as the
surface high passes off the coast.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Latest medium range guidance is showing an unusual lack of
spread among its members, all of which track a surface low
north of PA Saturday, with a trailing cold front coming through
Sat night into early Sunday. The lack of spread with regards to
timing of the front, combined with progged GEFS pwats of
+2-3SD, supports an increasing confidence in showers/tsra
Saturday. A leading warm front could produce showers/tsra as
early as Friday night and a slowing cold front could cause
convection to linger into Sunday, mainly over the southeast
counties. However, ensemble plumes indicate the most widespread
convection should occur Sat afternoon and evening.

There is some potential for severe wx Saturday PM, as decent
mid level flow overspreads an increasingly moist warm sector.
Ensemble plumes currently indicate moderate capes in the 1000
J/kg range and model 0-6km shear is in the 35-40kt range.
If the cold front slows enough, severe wx would also be possible
across the eastern edge of the forecast area Sunday PM.

Latest EPS and GEFS both support fair weather with near to
slightly below normal temps and low humidity early next week
associated with high pressure building east from the Grt Lks.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions are being observed across all of Central PA as of
05Z, but all guidance suggests that MVFR ceilings will develop
across the northwest by 09Z. These low clouds should dissipate
by mid morning and a period of VFR is expected area-wide through
at least the early afternoon.

Uncertainty begins to increase throughout the afternoon as there
are still questions about the timing of showers and
thunderstorms moving in ahead of a cold front. Showers are
likely to begin kicking up around 18Z in western PA before
overspreading to the east and strengthening through the
afternoon. A few of these storms could be strong to severe with
any impacted TAF site likely to see high wind gusts and briefly
lowered visibility. The best chance for strong storms will be
between 18Z Wednesday and 03Z Thursday. Have added broad periods
of VCTS at each TAF site, but this timing will have to be
refined with further forecast updates.

As the showers and thunderstorms exit to the east during the
late evening, guidance indicates the potential for low clouds to
stick around across a large portion of the area. The HREF shows
the highest probabilities of IFR ceilings (50-60%) at BFD and
JST, with lower probabilities of MVFR ceilings at all other
sites except MDT and LNS.

Outlook...

Thu-Fri...Generally VFR.

Sat-Sun...Thunderstorm impacts possible.

&&

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

&&

$$

SYNOPSIS...Lambert/Fitzgerald
NEAR TERM...Lambert/Fitzgerald
SHORT TERM...Lambert/Fitzgerald
LONG TERM...Fitzgerald
AVIATION...Bauco/Bowen