360
FXUS61 KCTP 050008
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
808 PM EDT Thu Jul 4 2024

.SYNOPSIS...
Warm and humid conditions will prevail through Saturday with
daily chances for showers and thunderstorms. A few storms could
produce strong winds and heavy rainfall this afternoon and
evening, especially in southern PA. Low pressure tracking north
of Pennsylvania will drag a cold front east of the state on
Saturday, ushering in drier and more comfortable conditions for
Sunday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Early evening update.

Area of showers and storms mainly east of our area now. Remains
of activity over eastern OH earlier now into western PA, but
weakening at this time.

Late afternoon update.

Two areas of showers and storms, one across the north dropping
southward, the other near the MD line. Updated weather grids
through 00Z. Very warm aloft and weak wind field, has resulted
in storms not being all that strong so far. Circulation center
over the Ohio Vly something to watch as we head into the
evening.

Earlier discussion below.

A weak, slow-moving and decaying cold front extending from the
Finger Lakes to the NW Mtns of PA will gradually drift south
through late this afternoon before washing out near or just to
the south of the Interstate 80 corridor tonight.

Latest mesoanalysis shows MU CAPE of around 2000 J/KG across
much of Central and Southern PA ahead of the front where SFC
temps have reached the upper 80s/low 90s and dewpoints were in
the upper 60s/low 70s.

Vertical shear is rather meager, so pulse storms or some multi-
cell clusters will be the primary storm mode/threat through this
evening.

Notable mid level capping with 700 mb temps in the 8.0-9.5C
range has challenged the updrafts from growing too strong/deep
so far and lightning has been virtually non-existent. Isolated
late day strong to SVR TSRA still appears possible given the
high CAPE values and local breaks through the aforementioned
where LLVL convergence is enhanced along the front, outflow
boundaries and terrain features.

The presence of +2-3SD pwats will bring the potential for
torrential downpours in some parts of Central and Southern PA
late this afternoon through about 01Z Friday.

The 00Z/12Z HREF indicates localized amounts to 3 inches are
possible across the southern tier, but dry ground in this part
of the state will limit the flash flood threat.

Passage of the shortwave with warm mid level air and nocturnal
cooling llvl cooling will result in dwindling convection by
later this evening. Slightly cooler air may work into the N
Mtns, as the front sags into the central part of the state.
Otherwise, expect a very warm and muggy night with min temps in
the upper 60s to low 70s. Patchy fog appears likely, especially
in locations that receive rainfall today.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Did cut POPS down for the morning hours, hard to see much
going on at this time of day, with warm mid levels.

Also did edge high temperature up a small amount, given the
airmass in place, and that I cut down the chc of showers and
storms in the morning hours.

Earlier discussion below.

High resolution guidance and the ensemble of its members shows
the potential for an area or two of heavy showers lifting NE
across the CWA within the warm sector late tonight into Friday
morning.

Leftover outflow boundaries, increasing/swrly deep layer shear
and healthy CAPE in the afternoon will set the stage for more
Showers/TSRA later in the day.

Previous...

The stalled front over Central PA is progged to return north as
a warm front Friday PM ahead of low pressure lifting across the
Great Lakes. Falling heights and surging pwats ahead of an
upstream shortwave and associated surface low lifting across the
Great Lakes should bring a round of showers/tsra in the latest
Friday PM to Saturday AM timeframe. Model shear/instability
profiles indicate strong to severe tsra can`t be ruled out Fri
PM. SPC expanded the previous DY2 MRGL risk area for SVR to
cover all but the far eastern parts of our CWA.

Current guidance suggests the mid level shortwave and bulk of
the large scale forcing will pass north of PA, leading to
unimpressive mean qpf in the ensemble plumes of 0.25 to 0.50
inches Fri PM to Saturday. However, locally heavier amounts will
accompany stronger convection. The Weather Prediction Center
has placed all of Pennsylvania in a Marginal Risk of Excessive
Rainfall for 8am Friday through 8am Saturday to account for
the multiple rounds of showers and potential for rainfall
amounts approaching 2 inches in a few spots. Flash flood
guidance across most of the region remains quite high (3" or
more in 3 hours), so most of this rainfall should be beneficial.

It is also worth noting that heat index values will approach
or briefly touch 100F on Friday afternoon in southeast PA.
Dewpoints in the low to mid 70s combined with high temperatures
approaching 90 will result in a very hot and humid afternoon.
With scattered convection in the forecast, there is not yet
enough confidence to warrant a heat advisory but one may need to
be considered if temps/dewpoints trend higher. Overnight lows
into Saturday will also be quite mild, ranging from the upper
60s in northwest PA to the middle 70s in the Lower Susquehanna
Valley.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
The aforementioned cold front is expected to mostly clear the
region by Saturday morning, but some lingering showers across
eastern Pennsylvania cannot be ruled out. Thunderstorms are
slightly less likely at this time given increased cloud cover
and lower instability of the early morning hours, but cannot
rule out a thunderstorm across far southeastern Pennsylvania
with some elevated instability. After the cold frontal passage,
cooler and less humid air will rush in by Sunday morning.

All medium range guidance supports fair weather and above
average temperatures Sunday into early next week with upper
level ridging indicated over the northeast. At the surface, high
pressure is progged to build over Pennsylvania Sunday, then
pass off of the east coast early next week. The return southerly
flow should result in an uptick in heat/humidity early next
week.

Diurnally driven showers and thunderstorms appear possible on
Monday based on recent GEFS plumes but guidance continues to
suggest a better chance of precipitation on Tuesday with the
arrival of a cold front during the afternoon hours. There is
still a fair amount of uncertainty with regards to the cold
front clearing eastern Pennsylvania later on Wednesday, so have
retained PoPs through this timeframe. Towards the end of the
period, deterministic guidance begins to outline high pressure
influence into the region; however, given so much uncertainty
earlier in the forecast period have opted not to deviate from
NBM PoPs at this time.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Showers and a few thunderstorms over the southeast will continue
to push off to the east into the late evening and will largely
be out of the area by 03Z. Another area of weakening showers is
moving in from the west ahead of an MCV located over western PA.
Most guidance indicates that a few showers will remain possible
across the northwest through the night.

Fog and low ceilings will likely develop across almost all of
Central PA overnight. The highest probabilities for IFR
visibilities are at BFD and IPT, and the highest probabilities
for IFR ceilings are at BFD, IPT, and JST. All other sites will
likely see MVFR conditions tonight with brief periods of IFR
possible.

Conditions will improve to VFR fairly quickly after sunrise
across most of the area, though it could take until late morning
for BFD and IPT to see the low ceilings improve. Scattered
showers and thunderstorms will be possible again Friday
afternoon, though coverage looks to be more limited than today.

Outlook...

Fri...Sct TSRA w/ possible impacts; Mainly PM w/ highest
coverage across the west.

Sat...Sct to Nmrs TSRA areawide, highest chances SE in PM.

Sun...AM fog possible; otherwise, no sig wx.

Mon...SHRA possible SE late PM; otherwise, no sig wx.

&&

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

&&

$$

SYNOPSIS...Lambert/Banghoff
NEAR TERM...Lambert/Banghoff/Martin
SHORT TERM...Lambert/Banghoff/Martin
LONG TERM...Fitzgerald/NPB
AVIATION...Bauco