004
FXUS61 KCTP 281758
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
158 PM EDT Fri Jun 28 2024

.SYNOPSIS...
*Seasonably warm and pleasant today; increasing clouds tonight
*Heat and humidity spike fuels severe T-storm risk this weekend
*Refreshing/dry start to July; heat+T-storms return by the 4th

&&

.NEAR TERM /THROUGH TONIGHT/...
Mostly sunny to partly cloudy and pleasant wx conditions across
central PA for the last Friday of June. Highs temperatures this
afternoon will range from 75-85F which is quite seasonable for
this time of year or within +/- 2 to 4 degrees of the historical
average for late June.

Increasing clouds expected tonight as warm air and moisture
advection ramps up across the area. There is a strong signal
for low clouds to develop/expand late tonight into early
Saturday morning particularly east of the Allegheny spine.

Still can`t rule out a couple of showers/elevated convection
over the far NW mtns prior to 12Z; however hires guidance
appears to be focusing in on a period of heavy rain in the
following 6hr pd.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
Latest HREF now shows 40-50kt LLJ from the south southwest
driving 2+ inch pwats into NW PA Saturday morning. The QPF
response is noteworthy with both 3/6hr PMM indicating 1-2
inches during the period ending 18Z Sat. If this signal remains
bullish with later hires ensembles, a short fused FF watch may
be needed given reduced FFGs over the NW/N-central zones
fostering increased vulnerability to short duration flooding.

The early morning low clouds forecast across the central mtns
into the Susquehanna Valley, along with the potential heavy
rainfall evolving across NW PA Saturday morning both complicate
the convective forecast for later Saturday afternoon and
evening. There is a conditional element now in play which hinges
on amount of instability/destablization that can be realized.

That being said, very little change to the SPC SWO for tomorrow
with the 1730Z update. 5% tornado risk remains largely unchanged
and hail probs were removed.

The belt of strong 850mb flow will transport rich low level
moisture (dewpoints in the upper 60s to lower 70s) northeastward
along/ahead of a cold front this weekend. PWAT values are
forecast to reach 2-2.5 inches on Saturday or +2-3SD. The
anomalous, deep-layer moisture will support risk of heavy to
potentially excessive rainfall with point amounts of 3 inches
possible in places experiencing multiple TSRA.

WPC added a SLGT risk across NW PA overnight which looks good
given increasing confidence in an initial round of +RA over that
area prior to 18Z. They may even expand the SLGT risk area a bit
with the next update later this afternoon/20Z. Storm motions and
much higher FFGs (due to lack of rainfall) will be limiting
factors to reduce flood risk farther to the south and east
across the CWA (where D0 and D1 drought conditions exist).

Convection/heavy downpours should be sustained after 00Z and
probably not exit the area until after midnight/06Z Sunday.

Guidance continues to show some variability with the timing of
the main frontal passage on Sunday. Locations most likely to see
potential strong/svr t-storms are over the southeastern part of
the CWA which is included in the D3 SLGT risk SWO.

Once the cold front clears, the door will be open for another
seasonably cool/dry airmass to invade the Commonwealth. This
will result in a less humid and comfortably dry start to July on
Monday.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
On the large-scale, a fairly zonal upper-level flow pattern
will stay in tact over the northern tier of states next week,
with energetic short-waves traversing this flow every 3-4 days
or so. Consequently, expansive summertime upper ridging will
largely stay south of PA, keeping excessive heat mainly out of
the forecast for the time being.

Looking at the daily sensible weather, as one of the above
mentioned short-waves presses through eastern Canada and New
England early next week, it will push a surface cold front well
to the southeast of the Commonwealth, bringing another stretch
of dry conditions and comfortable temperatures/humidity levels
for Monday and Tuesday. Confidence in this scenario is
relatively high.

By the middle of next week, as a surface high pushes offshore
and heights aloft begin to build, summertime heat and humidity
should at least temporarily make a run at PA. At the same time,
though, the next upstream surface cold front and upper-level
trough will be approaching from the northwest. The most likely
scenario here is for increasingly muggy conditions and higher
chances for showers and thunderstorms. Just how hot temperatures
are able to get, or robust convection becomes, is fairly
uncertain. Better knowledge of these factors will require
considerably more time and additional model runs to see how
atmospheric features resolve themselves during this time frame.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
VFR conds will prevail through Friday with primarily high
cirrus and fair weather cu expected. The exception will be
patchy valley fog in the northern Alleghenies early this
morning. Winds will start the day light and variable, then veer
to become S to SE later in the day on Friday with gusts
generally less than 20 kts.

As a warm front approaches late Fri night into Saturday,
southeast flow will bring increasing moisture and the potential
for low stratus across southern and eastern PA. Confidence is
relatively high in restrictions after 06z Sat for airfields from
UNV eastward, with a 25-50 percent chance of IFR conditions at
MDT and LNS. Overnight rain and some thunder is possible
especially in the north, mainly after 06z. Some marginal LLWS
is also possible mainly in the north.

The low stratus is expected to lift and become broken to
scattered before more numerous showers and thunderstorms
develop later on Saturday. The chance for showers and storms
will linger across the southeast into Sunday as a cold front
swings through the area.

Outlook...

Mon-Tue...Dry weather with VFR conditions.

&&

.CLIMATE...
Through 6/27, June ranks as the second warmest on record at
Harrisburg with an average monthly temperature of 76 degrees or
+3.8 degrees above normal.

&&

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

&&

$$

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