113
FXUS61 KCTP 170531
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
131 AM EDT Tue Jun 17 2025

.SYNOPSIS...
* Heavy rainfall may produced scattered to numerous instances of
  flash flooding across west central PA on Tuesday as a warm
  front lifts through the region.
* Moderating temperatures and scattered showers/thunderstorms on
  Wednesday will precede a risk for severe thunderstorms on
  Thursday ahead of and along an approaching cold front.
* Sunshine finally returns for Friday and Saturday before a
  strong ridge of high pressure ushers in a several day stretch
  of very hot and humid weather Sunday into early next week.

&&

.NEAR TERM /THROUGH TODAY/...
More of the same tonight into Tuesday morning with low clouds,
scattered light showers/drizzle, and southeast flow. Ridge
shrouding fog is a sure bet overnight with overcast skies and
the saturated airmass ensuring temperatures only drop a couple
degrees. Lows by daybreak Tuesday will be within a few degrees
of 60F (upper 50s north and lower 60s south).

The weather pattern on Tuesday looks particularly concerning for
flash flooding, especially across the western 2/3 of our
forecast area. Deep southwest flow along with an approaching
warm front will combine with anomalous PWAT values to generate
multiple rounds of training storms. Antecedent soil moisture
values are already quite high thanks to significant rainfall
over the past week (200% of normal along much of I-80). 35-45kts
of bulk shear will support convective development Tuesday
afternoon and locally enhanced rainfall rates over 1" per hour.

Showers and storms will develop across western PA during the
early afternoon and continue eastward with multiple rounds of
showers and storms affecting the region into the evening (and
perhaps overnight). A large area of 1-2" rainfall amounts
appears likely across much of Central PA (lower amounts
southeast of I-83 and north of US-6), with isolated amounts in
excess off 3" possible. WPC expanded the Slight Risk eastward
to US-15 with their Monday afternoon update, outlining the
threat for scattered flash floods. Locations along I-80 that are
most vulnerable to additional rainfall are progged to receive
the heaviest/most rain Tuesday afternoon. If current model
trends continue to paint the potential for multiple rounds of
showers and thunderstorms in west central PA and localized
amounts over 3", a Moderate Risk of flash flooding could be
issued. In addition, a Flood Watch will be needed for some or
most of Central PA Tuesday afternoon and evening.

Showers and storms should weaken overnight Tuesday with the loss
of daytime heating, thus reducing the threat for significant
flash flooding. Lingering showers will remain possible through
daybreak Wednesday, which could locally exacerbate any ongoing
flooding. If widespread, higher-end rainfall amounts are
observed, river flooding will be observed as well. Smaller
streams and creeks may need River Flood Warnings, with the most
likely basins affected being the West Branch Susquehanna
tributaries and Juniata Basin.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
PWAT values remain high on Wednesday under a prevailing upper
trough with winds finally turning southwesterly in the wake of a
warm front. This will support a bit more in the way of sunshine
by Wednesday afternoon along with some diurnally driven
thunderstorms. A surface low will pass just southeast of the
Commonwealth Wednesday afternoon, providing a bit of added shear
and lift for increased thunderstorm potential there. SPC and
WPC have included locations southeast of I-83 in a MRGL risk for
severe weather and flash flooding, though the threat appears
somewhat limited at this time. Highs Wednesday afternoon will be
noticeably warmer compared to recent days ranging from the mid
70s in the north to upper 80s in the Lower Susquehanna Valley.
Mild again Wednesday night with lows in the mid 60s to low 70s.

By Thursday, a mid-level trough will move across the Great Lakes
into the northeast, leaving Pennsylvania in a favorable
diffluent pattern aloft. Partly cloudy skies and increasingly
moist southwesterly flow should support scattered convective
development Thursday afternoon ahead of and along an approaching
cold front. 1500-2500 J/kg of MLCAPE, 30 to 40kts of bulk shear,
and steep low level lapse rates will support a considerable threat
for severe weather Thursday afternoon with the primary threat
being damaging winds. A Day 4 15% severe weather risk area from
SPC should convert to at least a Slight Risk for the Day 3
update overnight, with a future upgrade to an Enhanced Risk for
some portion of the Eastern Seaboard possible.

Highs Thursday afternoon will range from the mid 70s in the
northwest, where an early frontal passage will limit afternoon
temperatures, to near 90 in the southeast, where the front will
not cross until later in the day. The main fly in the ointment
for Thursday will be the timing of the front. A faster cold
frontal passage would limit the severe threat to eastern PA and
reduce the threat for Pennsylvania (lower afternoon high
temperatures as well). A slower progression of the front would
allow for more of the area to destabilize ahead of the front and
lead to an expanded risk of severe weather.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
The upper-level trough will gradually drift eastward on Friday
with slightly lower dewpoints and temperatures filtering in
behind the cold front. As upper ridging builds in, northwest
flow aloft will prevail through Saturday an Saturday night,
which will lead to continued diurnal shower/thunderstorm chances
through Saturday.

By Sunday, there is increasing confidence in a very strong ridge
of high pressure with 500mb heights approaching 600dm. 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 110F in the Lower
Susquehanna Valley. Although this forecast is still 7 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 TUESDAY THROUGH SATURDAY/...
06Z TAFS sent.

Main issue today into early Wednesday will be low CIGS.
Visibilities will low at times, mainy at night and in and
near showers and storms.

Chance for thunder will be a bit limited, unless low clouds
can break, and the airmass heated by the strong mid June
sun this aft.

No real change in the coming days.

Outlook...

Wed...VFR/MVFR with showers and thunderstorms possible, as warm
front pulls north of area.

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

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

&&

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

&&

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

&&

$$

SYNOPSIS...Banghoff
NEAR TERM...Banghoff
SHORT TERM...Banghoff
LONG TERM...Banghoff/NPB
AVIATION...Martin
CLIMATE...Steinbugl