Severe Thunderstorm Warning 103, NWS State College, PA

Area Forecast Discussion
National Weather Service State College PA
325 PM EDT Wed Jun 18 2025

.SYNOPSIS...
* Strong to potentially severe thunderstorms remain possible
  Thursday afternoon (risk level 2 out of 5) as a cold front
  moves in and through PA.
* The first significant heat wave of the season is expected from
  Sunday into early week, with Major Heat Risk forecast (level 3
  out of 4).

&&

.NEAR TERM /UNTIL 11 PM THIS EVENING/...
Plenty of boundaries around now with sct/nrms SHRA/TSRA
surrounding the CWA with the very first TSRA of the day now into
Clearfield Co. Earlier +RA in nrn Clearfield Co has tapered off,
but additional SHRA/TSRA to the west may move into that wet
area. SVR watch covering the SE 3 Cos is where it makes the most
sense. The CAPE is biggest there and shear of 35KT is not too
shabby. But, thus far, only relatively short storms have
developed N of the MD border. Earlier lake breeze convection has
stayed away for the most part, but what started on the OH
stretch of the lake is now sliding into NWrn PA. Thus, there are
multiple reasons to keep PoPs very high across the area. The
only negative is that the SHRA/TSRA are rather scattered about.
So, coverage being low, but having multiple chcs at rain yields
PoPs in the 60-90pct range for the rest of the daylight hrs.

&&

.SHORT TERM /11 PM THIS EVENING THROUGH 6 PM THURSDAY/...
As the sun sets and we start to stabilize, the best forcing
will also slide to the east. So, the first part of the night
should be quiet/rain-free over most of the area. There will
still be a few more shots of forcing move into the west. So, we
can't rule out additional SHRA/TSRA overnight in the western
highlands. Temps will dip only slightly and hit the dewpoint in
lots of places. There could be areas of fog form over the
eastern half or so of the CWA tonight, but, the wind expected in
the higher elevations will probably keep fog from getting bad
enough to notice in the west/north. Of course, places that have
had rain and little/no time to dry out before sunset will be
the most likely places for fog to form. Mins 65-70F are real
summer values as we get close to the longest day of the year.

The approach of a long wave trough aloft will put us in the
favorable right entrance region of a jet streak moving poleward
on Thursday. The cold front associated with this trough will be
arriving in Central PA in peak heating/mid-day and shear also
increases to 40+KT over most of the area. Expect SHRA and
perhaps a TSRA or two to be onging in the AM over wrn PA and
fire up over the CTP CWA in the late morning and aftn. As the
day continues, the CAPEs in the SE get back into the 1500-2000J
range in the E. The SPC SLGT risk of severe remains in place for
good reasons. Flooding should be much less of a concern Thurs vs
Wed with storm motions much quicker despite PWAT values of
1.5-2" (highest E). Still a MRGL risk of excessive rain, though,
as repeated cells could make for localized problems. Not enough
of a risk nor confidence to post a FF Watch at this point.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Main change to the package was minor adjustments to the
Saturday, as convection can drop southeast across the top
of the upper level ridge into our area. Still looks hot
as we head into the start of the week, but always a chance
for convection to drop into area, given the type of airmass
in place, and the wet ground from recent rains.

Earlier discussion below.

As upper ridging builds in, a strong capping inversion (with mid
level temps peaking in the 12-13C range over the weekend) will
greatly limit any shower/thunderstorm chances to sub 20 pct for
Sat-Mon.

By Sunday, highs in the low to mid 90s are becoming more likely
as a very strong ridge of high pressure with 500mb heights
approaching 600dm builds overhead. NAEFS guidance depicts a ~72
hour period of anomalous 500mb heights, 700mb temperatures, and
850/925mb specific humidity values (>99th percentile for this
time of year). If such a forecast materializes, we could be
looking at a several day stretch of extreme heat and humidity
across the region. Monday looks to be the hottest day of the
stretch, with highs currently forecast in the 90s for most of
the area. Dewpoints in the mid 70s would push heat index values
over 100F for most locations east of I-99 and south of I-80,
with values approaching 105+ in the Lower Susquehanna Valley.
Although this forecast is still several days out and uncertainty
remains, the fact that we have been in a stretch of relatively
cool conditions means the quick switch into significant heat and
humidity could exacerbate the risk for heat-related impacts.

In addition to warm afternoon temperatures and heat index
values, overnight lows will provide little to no relief from the
heat. With the expected stretch of hot and humid conditions, those
with heightened susceptibility to heat, such as young children,
older adults, people with chronic medical conditions, and
pregnant women, should prepare to limit time outdoors, wear
light clothing, and drink plenty of water later this weekend
and early next week.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Looking at some pop up showers and storms this afternoon, as
the airmass heats up.

Will continue to adjust fcst as needed.

Earlier discussion below.

A few strong t-storms are possible particularly in the vicinity
of KMDT and KLNS and have included PROB30s with the 18/06Z TAF
cycle. Overall convective coverage does not appear to be as
widespread as yesterday with mainly dry wx probable for the
central and eastern airspace overnight. Latest guidance
supported adding LLWS to the western and central airfields as
LLJ increasing from ~240 degrees into early Thursday morning.

Outlook...

Thu...Predominantly VFR, although strong PM t-storms are
possible with a cold frontal passage.

Fri...Predominantly VFR, with a slight chance of a rain shower
north.

Sat-Sun...Mainly VFR. Hot.

&&

.CLIMATE...
A daily record rainfall of 1.72" was set at Altoona yesterday
6/17. This broke the previous record of 1.22" set in 1978.

Astronomical Summer (solstice) officially arrives on Friday,
June 20, at 10:42 p.m.

&&

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

&&

SYNOPSIS...Dangelo
NEAR TERM...Dangelo
SHORT TERM...Dangelo
LONG TERM...Steinbugl/Martin
AVIATION...Steinbugl/Martin
CLIMATE...Steinbugl

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