Altoona, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

197
FXUS61 KCTP 042330
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
730 PM EDT Sat Jul 4 2026

.WHAT HAS CHANGED...
* Added more details for the severe thunderstorm potential this
  afternoon and evening, with a mesoscale update.
* Increasing confidence in heavy rainfall signal across
  portions of central Pennsylvania, with highest uncertainty in
  the exact placement of this heavy rainfall.

&&

.KEY MESSAGES...
1) Hot and humid conditions for Independence Day will bring
another round of strong-to-severe thunderstorms with an
increased risk for damaging winds.

2) Chances of showers and storms become more widespread on
Sunday and Monday, bringing both severe and flooding concerns
for the end of the weekend and into the first of next week.

&&

.DISCUSSION...
KEY MESSAGE 1: Hot and humid conditions for Independence Day
will bring another round of strong-to-severe thunderstorms with
an increased risk for damaging winds. A Severe Thunderstorm
Watch is in effect for portions of western Pennsylvania.

Current heat index values in the upper 80s to lower 100s across
central Pennsylvania are currently being observed as of 1PM,
which jives well with out current heat products (see NPWCTP) in
effect through 8PM this evening. In short, very few changes to
the temperature/dewpoint forecasts with the main changes in
near-term dewpoints with the NBM pushing two to three degree to
warm and pushing heat index values higher than could be expected
across portions of northwestern Pennsylvania. At this time,
products look good to be dropped this evening with no heat
products expected to be issued for tomorrow. It will still be
warm and humid; however, with heat index values still reaching
into the mid-to-upper 90s across the Lower Susquehanna Valley,
so still good to continue precautions for heat-realted illnesses
given the duration of this heat wave.

In terms of severe threat, today`s set-up looks fairly similar
to yesterday`s in the fact that we are looking at an ample
amount of instability and not the most favorable shear profiles
across central Pennsylvania. We`ll likely see some initial cells
starting to pop-up over the next couple of hours both across
northwestern Pennsylvania and southwestern Pennsylvania. These
cells could initially struggle and have more of a pulse
thunderstorm nature at first given the lack of favorable bulk
shear; however, generally expectations are for some stronger-
to-severe thunderstorms to begin to form and sustain themselves
into the late afternoon and evening hours. Recent SPC
Mesoanalysis outlines extremely favorable DCAPE values, in the
1200-1400 J/kg range across portions of southern Pennsylvania as
of 17Z/1PM EDT. This indicates that while coverage of storms
remains uncertain moving into the afternoon hours, damaging wind
potential within storms will be extremely plausible given
favorable DCAPE values and higher LCLs that would promote
downburst potential. For thunderstorm development across
northwestern Pennsylvania, DCAPE values are not as impressive,
but still soar fairly well into the 900-1000 J/kg range which
will still be sufficient for some downburst potential,
especially with *slightly* more shear up that way. MCD#1492 from
SPC generally mirrors those thoughts. This threat will
gradually shift towards eastern Pennsylvania later this evening,
where similar sentiments with regards to if there is a
thunderstorm, damaging winds are plausible continue.

Storms today will likely bring some locally heavier downpours
with storm motion likely between 25-40 knots, thus while we
cannot rule out some localized flash flooding, this would be
limited to areas that receive multiple rounds of stronger
thunderstorms. Ample low-level moisture overnight will bring
some potential for locally dense fog across the ridges of
central Pennsylvania with could make travel tonight into Sunday
morning hazardous for those driving to/from locations with
Independence Day activities.

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

KEY MESSAGE 2: Chances of showers and storms become more
widespread on Sunday and Monday, bringing both severe and
flooding concerns for the end of the weekend and into the first
of next week.

Recent HREF ensemble guidance and hi-res model guidance
indicate some precipitation around the area late Sunday morning
into the early afternoon hours before a general increase across
the board on shower/thunderstorm coverage. The air mass across
central Pennsylvania will be fairly moist, with HREF guidance
indicating PWATs approaching in the 1.50-1.75" range across N/W
PA with some locations in SE PA approaching 1.75-2.00" PWATs by
the afternoon and evening hours. For reference to climatology
if this solution pans out, this would be in the 90th to 95th
percentile for PWATs for the beginning of July. Recent NBM QPF
forecast brings 1.50-2.00" of rainfall into portions of SE PA on
Sunday, with heaviest rain expected in the afternoon and
evening hours with some heavier rain considering overnight into
Monday morning. This heavy rain signal is matched in recent HREF
ensemble guidance, with 24 hour LPMMs outlining some spot
amounts between 3-4" for this same timeframe. This signal for
heavy rain will bring some flooding concerns to the more
urbanized corridors of SE PA, which is matched in the Slight
Risk for Excessive Rainfall from WPC. The main thing that would
preclude flooding concerns would be the fact that this area is
in Severe (D2) Drought based on the most recent Drought Monitor;
however, heavy rain will still very well cause instances of
flash flooding. This heavy rain signal will be in place on
Monday; however, slightly less rainfall forecast on Monday and
will have to see what rainfall this evening though Sunday brings
to the region before reading too much into this threat. There
also will be some severe threat stationed across southern
Pennsylvania, mainly south of the I-80 corridor with damaging
winds being the main concern given ample instability in place.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Back to aviation after brief break from earlier aviation duties.

Main change was to adjust fcst to current obs and radar. Severe
storms in the MDT area and just a few minutes away from LNS.

Earlier information below.

For the 18Z TAF package, main change is to slow down the start
time of showers and storms. This based on a similar pattern
to what we had yesterday. Also lower dewpoints and more of a NW
wind so far today. Yesterday storms fired up across the north
during the early to mid afternoon hours, and stayed northeast of
MDT and LNS.

Another set of storms moved eastward into central PA toward UNV
by late evening.

The airmass so far today has dewpoints lower than the last few
days. Maybe not a huge factor for humans, but storms are happy
with the more humid airmass, thus a slight change in moisture
can lead to large changes in the outcome.

The other change was to add more detail later tonight into
Sunday, where some fog and lower CIGS possible, mainly in
spots like BFD and IPT and in areas that get some rain.

Lower CIGS Sunday could occur and linger behind the front if
widespread showers form early enough, before heating takes hold.
Poor conditions could occur from time to time right into Tue,
before some improvement by mid week.

Outlook...

Mon-Tue...Restrictions possible in A.M. fog and P.M. T-storms.
Wed-Thu...Improving conditions expected.

&&

.CLIMATE...
Williamsport tied their record max 7/3/26 (100F in 1966).

Record maxes for the next few days:

Station/Date...07/04...07/05
MDT.............104.....102
IPT.............100.....100
AOO............. 97......94
JST.............100.....101
BFD..............91......91

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT this evening for PAZ019-025>028-
034-045-046-049>053-058.
Extreme Heat Warning until 8 PM EDT this evening for PAZ035-
036-056-057-059-063>066.

&&

$$

WHAT HAS CHANGED...Beaty
KEY MESSAGES...Beaty
DISCUSSION...Beaty
AVIATION...Martin
CLIMATE...Steinbugl