Latest Area Forecast Discussion for Central PA

Here is the latest Area Forecast Discussion for Central PA

This text statement is the latest forecast reasoning from the NWS in State College, PA

See the links at the bottom of the page for previous issuances/versions of the statement as well as our other text statements.

844
FXUS61 KCTP 181850
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
250 PM EDT Mon May 18 2026

.WHAT HAS CHANGED...
* Day 2 SPC Outlook upgraded to a Slight Risk (Level 2 out of
5) for damaging winds in northwest PA.

&&

.KEY MESSAGES...
1) Hottest temperatures of the year so far forecast this
afternoon along with some scattered storms in south central PA.

2) More heat & humidity will produce scattered showers and
thunderstorms on Tuesday afternoon and evening, some of which
could be strong to severe, especially across northern PA.

2) A strong cold front to bring showers and thunderstorms with
the potential for severe weather on Wednesday followed by
colder temperatures.

&&

.DISCUSSION...
KEY MESSAGE 1: Hottest temperatures of the year so far forecast this
afternoon along with some scattered storms in south central PA.

An expansive deck of fair weather cumulus had developed across
the Commonwealth this afternoon with very warm temperature and
sticky-but-not-overly-humid dewpoints. Convection has begun to
fire in the West Virginia panhandle and will continue to extend
north-northeastward this afternoon and evening as temperatures
continue to rise under an anomalous upper level ridge. 500 mb
heights per the GEFS will rise to near 590mb this afternoon
across southeast PA, correlating to standardized anomalies of +2
sigma along the Mid Atlantic Coast through 18z Tuesday.

We collaborated with LWX and SPC to paint a MRGL risk for SVR
TSRA this afternoon from the Scent Mtns to the West Branch
Valley of the Susq. This corridor will be near the eastern edge
of somewhat stronger (35-40 kt) swrly mid level winds with MU
CAPE reaching near 2000 J/KG. Additionally, the eastern edge of
an elevated mixed layer (currently over the Middle Ohio River
Valley) will be tracking ENE at 15-20 kts and reach the western
edge of the MRGL Risk area around 22-23Z today helping to
enhance mid level lapse rates and updraft intensity. The primary
hazard with these pulse storms will be the potential for gusty
winds associated with the the clearly high- based convection
occurring within an inverted-V sounding.

Daily record highs could be challenged in some locations. See
the Climate section for more details. Manual adjustments were
made to lower NBM maxT by a few degrees today due to a known
systematic bias correction issue identified during the shoulder
seasons. This should also keep max heat indices under 100F,
precluding any need for Heat Advisories. Still, heat risk
impacts will continue to be monitored given the quick ramp-up in
heat and limited acclimation time.

Dewpoints over 60F for many will also feel more humid relative
the recent cool stretch we`ve had.

-------------------------------------------------------------

KEY MESSAGE 2: More heat & humidity will produce scattered
showers and thunderstorms on Tuesday afternoon and evening, some
of which could be strong to severe, especially across northern
PA.

By Tuesday, we`ll still be under the influence of the
anomalously strong ridge of high pressure, with broad
southwesterly flow continuing to pump warmer temperatures and
humid conditions into Pennsylvania. Highs on Tuesday should be
fairly comparable to today, though afternoon showers/storms in
the west could limit how warm it gets there.

At the surface, a deepening surface low will lift across the
Great Lakes with gradually sinking heights aloft impinging
northwest PA. Underneath this sprawling ridge, Pennsylvania
will be in a moist and unstable airmass with MUCAPE values
expected to reach 1000-1500J/kg. With marginal but sufficient
shear, this amount of instability could support a few stronger
storms will strong to damaging wind gusts. The SPC upgraded NW
PA to a Slight Risk (Level 2 out of 5) of severe weather Tuesday
afternoon. The Marginal Risk extends down to about halfway
between I-80 and I-76. Low level hodographs do exhibit some
spin and an isolated tornado cannot be ruled out in northwest PA
closer to the parent surface low pressure system. CAMs disagree
on the extent to which convection initiation will occur Tuesday
afternoon, but the heat and humidity will provide as much fuel
for storm development as we`ve seen yet this year.

Rainfall amounts are not expected to be all that impressive with
this system, largely owing to unimpressive/relatively dry
moisture profiles with dewpoints in the upper 50s to low 60s.
The good news is that these lower dewpoints will keep our heat
index values below 100F and mitigate the need for Heat
Advisories across the area. Rainfall amounts will be highest
west of I-99 and locations farther east may not see much rain at
all before Wednesday.

--------------------------------------------------------------

KEY MESSAGE 3: A strong cold front to bring showers and
thunderstorms with the potential for severe weather on Wednesday
followed by colder temperatures.

A cold front (accompanied by more widespread and frequent
showers/t-storms) brings relief to the relatively short bout of
heat and moderate humidity Wednesday into Thursday. High
temperatures on Wednesday in northwest PA (behind the front)
will be nearly 20 degrees cooler than Monday/Tuesday. The Lower
Susquehanna Valley will squeak out another warm day with highs
in the upper to 80s to near 90F.

Ahead of and along the front, there will be a risk for severe
weather again on Wednesday. The magnitude & location of the
severe threat will be highly dependent on cold front passage
timing and amount of cloud cover in advance of the frontal
boundary. A Marginal Risk area covers locations south and east
of the I-80/I-99 corridor and highlights locations along and
downstream of the cold front between 12PM and 8PM on Wednesday.
A few of the hi-res models depict a slower cold front passage.
Such a solution would allow for more destabilization ahead of
the front and a higher threat for damaging straight line winds.
If the front ends up being faster than progged, clouds/rain in
the morning could limit instability and lead to an unimpressive
gusty shower event. Regardless, this system will feature
beneficial rainfall with rainfall amounts generally 0.10-0.25"
and locally higher totals possible in thunderstorms.

In the wake of the cold front, high pressure will build in for
a short time. Temperatures are forecast to cool down back to
historical/climo averages for late May for the end of next week.
Early indications show the aforementioned cold front stalling
out south of the Mason-Dixon line late in the week and lifting
back north across PA as a warm front into Memorial Day weekend.
The current outlook favors a cooler/wetter stretch through the
holiday weekend thanks to that warm front, but there is still
a lot of time for the forecast to trend in a more favorable and
optimistic direction for the holiday weekend that marks the
unofficial start of summer.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
Scattered cumulus clouds have been noted moving over the central
Pennsylvania air space. Flight conditions are expected to remain
VFR throughout the TAF period outside of a an isolated
thundershower this afternoon. Confidence is overall low on
thunderstorm development this afternoon. Forcing for storms is
weak despite the available energy in the atmosphere. Latest CAM
guidance would indicate a narrow window for convective storms to
develop after 22Z this afternoon. These storms will be very
isolated in nature, and PROB30 groups have been included at
airfields that may see one of these storms.

Overnight, a shortwave tracking across the Great Lakes may
result in a few showers/thundershowers across West-Central PA
(mainly KBFD), though flight restrictions appear unlikely with
this activity. After 12Z on Tuesday clouds will begin to scatter
out again and clear, with wind gusts up to 25kts possible again
on Tuesday throughout the afternoon.

Outlook...

Tue...Mainly VFR. Patchy A.M. fog possible. Isolated P.M.
shower or t-storm possible.

Wed...Restrictions probable through Wednesday night with
widespread showers/storms along CFROPA.

Thu...Lingering showers across S PA, restrictions possible.

Fri...Lingering showers across S PA, restrictions possible.

&&

.CLIMATE...
Daily record max temperature for May 18-19:

5/18 5/19
Harrisburg 94 in 1962 95 in 1962
Williamsport 95 in 1962 96 in 1996
Altoona 91 in 1962/1996/2017 92 in 1996
Bradford 85 in 1962 85 in 1962
State College 92 in 1962 92 in 1934/1996

Overnight low temperatures on Monday night into Tuesday are also
in jeopardy.

Please note: State College Co-operative observations are a
24-hour summary taken once per day around 7 AM (7AM-7AM).
Therefore, a max temp occurring in the daylight or late in the
day is usually reported in the _next_ day`s observation. Also,
the same min temp may be reported on two consecutive days if the
min occurs at observation time.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Air Quality Alert until midnight EDT tonight for PAZ057-059-
063-065-066.

&&

$$

WHAT HAS CHANGED...Banghoff
KEY MESSAGES...Banghoff/Ciampi
DISCUSSION...Banghoff/Ciampi
AVIATION...Bowen/Teare
CLIMATE...Dangelo/Steinbugl

Forecaster's
Discussion: