156
FXUS61 KCTP 261752
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
152 PM EDT Wed Jun 26 2024

.SYNOPSIS...
*Clusters of thunderstorms accompanied by potentially damaging
 wind gusts and heavy rainfall are possible later this afternoon
 through the evening
*Partly to mostly sunny and less humid Thursday and Friday
*Return of summertime heat+humidity will fuel thunderstorms for
 the last weekend of June; seasonably cooler & dry start to July

&&

.NEAR TERM /THROUGH TONIGHT/...
1230PM/1630Z: Noteworthy changes since the previous AFD update:

1) WPC upgraded to a SLGT risk ERO (level 2 out of 4) for the
northwest portion of central PA. There has been a growing
signal for upper level support during the afternoon/evening hours
to enhance forcing/lift over this region to boost rainfall
intensity, especially from eastern Ohio to northern Pennsylvania.
Training of storms in the west-east orientation along diffuse
sfc boundary will be capable of upwards of 3 inches per hour
rain rates that will more than likely reach or exceed the local
FFG. The 26/12Z HREF PMM and 3hr QPF neighborhood probs of >1"
& >3" highlight the heavy/excessive rain threat quite well.

2) There was some internal conversations about a possible SWO
upgrade from SLGT to ENH, but ultimately consensus was to
maintain the SLGT risk. Latest MCD#1426 just issued covering
most of north central PA indicates severe storm risk is ramping
up given strong heating with growing cu field south of the PA/NY
border. The expectation is for storm coverage and intensity to
increase mainly after 18Z with scattered damaging gusts most
likely within corridor of strongest deep layer mean winds/shear.
SPC also reintroduced a 2% tornado probability. Probability of
watch issuance...60 percent

1100AM/15Z: 13Z updated SPC SWO expanded the SLGT risk (level 2
out of 5) northward to include all of the CTP forecast area.
HWO was updated to reflect this change. We also included
damaging winds and heavy rain as potential severe t-storm
attributes. Latest hires models depict initial t-storms
developing across northwest PA by 4pm/20Z (where 15Z SPC RAP
mesoanalysis shows 2000 J/kg of SBCAPE with SBCIN eroded over
all but the far southeast zones) before increasing in coverage
spreading/evolving to the east and south through 8pm/00Z. QPF
signal appears to be focused across north central PA through 00Z
then shifting to the southeast half of the CWA between 00-06Z
as storms track from NW to SE. Increased POPs during the first
half of tonight based on the latest NBM 1 and 3hr PPIs. Max
temps still expected to peak between 80-95F this afternoon.

Previous Discussion Issued: 456 AM EDT Wed Jun 26 2024

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 (less
humid) 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
with valley fog formation likely given air/water spreads 20-30
degrees. Partly cloudy 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. Latest model data suggests some showers and storms may
develop Friday night over the western portion of the forecast
area.

&&

.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. A
seasonably cool and dry start to July!

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
VFR conditions across Central PA at midday, but thunderstorm
chances increase into the evening hours. 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.

Tstms already popping up over NW PA with convective impacts in
the vicinity of BFD and occasional impacts/reductions at the
airfield through around 21z. Convective activity picks up later
in the afternoon for the central mountains stretching from JST-
AOO-UNV-IPT. An isolated tstorm is poss in the vicinity through
21-22z, with likely impacts/reductions from tstms moving across
the airfields around 00z. Similar setup over the SE where an
isolated storm will be possible through 00z near MDT-LNS ahead
of better likelihood of impacts after 00z.

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.

Mon...Generally VFR.

&&

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

&&

$$

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