016
FXUS61 KCTP 180216
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1016 PM EDT Tue Jun 17 2025

.SYNOPSIS...
* A mild and rather muggy night with diminishing showers and
  patchy fog then warmer and humid Wednesday with a few showers
  likely and scattered afternoon thunderstorms
* Strong to potentially severe thunderstorms possible Thursday
  afternoon
* First significant heat wave to the season expected Sunday into
  early week with Major Heat Risk forecast (level 3 of 4)

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Mixed Layer CAPE and the associated coverage and intensity of
showers was steadily waning over the past few hours and have
allowed the Flood Watch to expire on schedule at 02Z Wed.

We`ll see a relatively min in showers for the middle half of the
night with some patchy fog forming in any areas that see some
brief periods of clearing through the otherwise expansive
multi-layered cloud deck.

Better llvl jet energy/moisture transport and deep layer lift
moving back into our Western zones toward daybreak, helping to
expand both the coverage and intensity of SHRA and possible TSRA
for a several hour period, especially over the SW third of the
CWA.

Min temps will be mild and in the mid to upper 60s in most
places and around 70F in the Scent Valleys.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY NIGHT/...
Another midlevel shortwave trough is fcst to move through the
central Appalachians by 00Z Thu along the northwest periphery of
the upper level ridge off the Carolina coast.

Sfc warm front moves a bit more to the east across the CWA on
Wednesday, but should linger across the Susq Valley into the mid
afternoon hours providing the focus and llvl shear for some
robust convection as noted below in the previous disc.

Previous...

Rather strong heating of a moist environment will result in
moderate to strong buoyancy Wednesday afternoon particularly
across southeast PA. Scattered diurnal storm development will be
possible with guidance generally depicting a belt of 35-45 kt
midlevel flow across the region. This modest flow enhancement
could result in some storm organization, with large PW and
steepened low-level lapse rates resulting in a threat for at
least isolated damaging wind. The D2 MRGL risk SWO clips the
eastern portion of the lower Susquehanna Valley.

By Thursday, a seasonably deep 500mb trough will move across
the Great Lakes into the Northeast CONUS. With rich moisture
already in place, it won`t take much heating to drive
thunderstorm development Thursday afternoon ahead of and along
an approaching cold front. Timing of the cold front still varies
somewhat which adds an element of uncertainty to the severe
storm potential. That being said, SPC transitioned the D4 15%
severe prob to a D3 SLGT risk SWO which essentially covers the
southeastern 1/2 of CWA.

Higher confidence outcome is the front clears the area Thursday
night which will bring drier/less humid conditions to close out
the week an officially kick of astronomical summer (see climate
section).

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
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 /02Z WEDNESDAY THROUGH SUNDAY/...
As of 19z, MVFR to IFR cigs blanketed central PA, with satellite
imagery showing any improvement confined to Somerset County.
Showers and thunderstorms will become more numerous, with the
heaviest activity in the afternoon hours expected around JST.
The heaviest rain is expected prior to 02z Wed. Later tonight,
cigs are expected to lower across much of the area, with IFR to
LIFR conds expected for most airfields. The highest chance for
LIFR cigs (30-40 pct) will be across the southeast (MDT, LNS).
Conditions will generally improve into Wed afternoon, with most
sites improving to MVFR. Showers and thunderstorms are expected
again Wed afternoon.

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

&&

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

&&

$$

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