799
FXUS61 KCTP 190555
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
155 AM EDT Thu Jun 19 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 8 AM THIS MORNING/...
One wave of convection is exiting our eastern zones late this
evening and a second is knocking on the western doorstep.

First wave of convection supported by llvl convergence along a
lingering/dissipating quasi-stnry boundary beneath the right
entrance region of a moderately stg mid/upper level jetlet.

Second round of convection entering NW PA is being fueled by
increasing PWAT air being advected NEWD at the nose of a 40-45
KT LLJ. EHIs have increased back into the 1-1.5 M2/S2 range
between KPBZ and Interstate 80, and this increasing instability
and low-mid level shear/forcing will maintain (or even
strengthen slightly) the line of strong to svr tsra moving over
the PA/OH border.

In addition to the severe threat the tail end of this line may
very well become more parallel with the backing/swrly deep layer
shear vectors which could leading to training of +SHRA/TSRA and
increase the flooding threat over parts of the Western
Mtns during the predawn hours.

Much of the night across the eastern half of the CWA should stay
dry as the main push of deep layer forcing pushes NE into
upstate NY.

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.

&&

.SHORT TERM /8 AM THIS MORNING THROUGH 6 PM FRIDAY/...
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 ongoing 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 /FRIDAY NIGHT THROUGH WEDNESDAY/...
Heights aloft gradually rise as we head through the upcoming
weekend, culminating in an expansive 500 mb high centered over
the Ohio Valley and Central Appalachians by late Sunday.

Height anomalies at 500 mb and 250 mb will be in the 2-3 sigma
range. Furthermore, the axis of the upper level ridge appears to
give little chance of having some temporary cooling from ring of
fire convection dropping SE into PA from the Glakes.

A strong capping inversion (with mid level temps peaking in the
12-13C range over the weekend) will greatly limit and likely
negate any airmass/orographic shower/thunderstorm chances to
sub 15 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.

The heat only decreases slightly toward the middle of next week
with heights at the center of the upper level ridge falling by
about 50-60 decameters and GEFS Mean temps in the 925-850 mb
layer dipping by 1-2 deg C from Mon/Tue to Wed.

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 /06Z THURSDAY THROUGH MONDAY/...
A weakening line of convection moving in from the west will
bring a few showers and maybe a thunderstorm to BFD and JST
through 09Z. Most guidance suggests that these showers and
storms will struggle to make it any farther east than AOO and
UNV. A brief dry period is then expected into the early
morning. Fog has developed across much of the northern half of
PA, though it has largely stayed away from any of the TAF sites.
Model sounding suggest that the best chance for visibility
restrictions will be at IPT. Fog will quickly dissipate after
sunrise.

A 40 to 45 knot low-level jet will move into southwestern
Pennsylvania prior to sunrise, but the threat for LLWS appears
low as the strongest winds should remain above 2000 feet. The
threat completely goes away by mid morning as surface wind gusts
begin to increase into the 20 to 25 knot range.

The main concern for Thursday is an area of low pressure
tracking to our northwest which will bring renewed chances for
showers and storms. Scattered showers will first develop in the
14-15Z timeframe across the western mountains and will gradually
spread eastward into the afternoon. As the surface cold front
associated with the low pressure system enters the region during
the afternoon, expect additional showers and thunderstorms to
develop. Some of these storms will be strong to severe and may
produce strong wind gusts, particularly across southeast PA (MDT
and LNS).

Showers and thunderstorms will exit to the east after 00Z Friday
and winds will become west-northwesterly behind the departing
cold front. This will allow for MVFR ceilings to develop at BFD,
JST, UNV, and possibly IPT, while skies begin to clear out to
the southeast.


Outlook...

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

Sat-Mon...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...Lambert/Dangelo
NEAR TERM...Lambert/Dangelo
SHORT TERM...Lambert/Dangelo
LONG TERM...Lambert/Steinbugl/Martin
AVIATION...Bauco
CLIMATE...Steinbugl