992
FXUS61 KCTP 261901
AFDCTP

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

.SYNOPSIS...
*Clusters of severe thunderstorms with heavy rainfall remain
 possible 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 /UNTIL 6 AM THURSDAY MORNING/...
300PM/19Z: Severe tstm watch #464 remains in effect for north
central PA until 9PM. Radar shows robust 50-60 dBZ cores
penetrating above the -20C level from Warren to Potter County
prompting severe tstm warnings with wind/hail threat across
portions of northwest and north central PA. Focus should trend
toward hydro concerns across the northern tier with increasing
pwats and saturated/narrow CAPE profiles. WoFS 90th percentile
run total QPF shows a stripe of 2-3" along llvl convergence zone
over the northern tier. Farther to the south/east, a dmg wind
threat may emerge through afternoon with steep mid level lapse
rates and higher DCAPEs with southern extent.

Hires models show rain and storms progressing from northwest to
southeast btwn 00-06Z with a general weakening trend expected
as BL stabilizes after sunset.

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.

&&

.SHORT TERM /6 AM THURSDAY MORNING 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 WEDNESDAY/...
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 /19Z 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