855
FXUS61 KCTP 040959
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
559 AM 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 /THROUGH TONIGHT/...
Starting out the day with mostly cloudy skies and uncomfortable
humidity. Isolated showers are observed on radar this morning
and will continue this morning, primarily in the vicinity of a
decaying cold front over Northern PA. Convection will increase
in coverage by afternoon, as a weak shortwave approaches from
the Southern Great Lakes. Model RH profiles suggest mostly
cloudy skies are likely. However, even modest diurnal heating of
this high- pwat airmass should yield moderate capes of near
1000 J/kg south of the front.

Deep layer shear profiles are not especially impressive today,
but the combination of instability and shear yields decent
updraft helicity values across the southern tier of the state,
where isolated late day severe weather appears possible. The
combination of instability and +2-3SD pwats could yield
torrential downpours in some parts of Southern PA Thursday
afternoon. The 00Z 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. Highs
this afternoon will generally be in the 80s with a few spots
potentially reaching 90 degrees in the southeast before
convection arrives.

Passage of the shortwave and nocturnal cooling should result in
dwindling convection Thursday night. 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 /FRIDAY THROUGH SATURDAY NIGHT/...
Latest high resolution guidance indicates a slug of heavy
moderate showers could be present across northern PA on Friday
morning, helping set the stage for more rain later in the day. 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 Friday
PM to Saturday AM timeframe. Model shear/instability profiles
indicate strong to severe tsra can`t be ruled out Fri PM. The
trailing cold front should clear most of the region by Sat
morning, but could take until afternoon clear the southeast
counties, where the threat of a tsra will linger.

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. After the cold front sweeps through on Saturday, cooler
and less humid air will rush in by Sunday morning, with lows
progged in the middle 50s NW to near 70s SE.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
All medium range guidance supports fair weather and above
average temperatures Sunday into early next week with upper
level ridging indicated over the Northeast CONUS. At the
surface, high pressure is progged to build over PA 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. 18Z GEFS plumes suggest isolated PM convection is possible
Monday. However, the much better chance of showers/tsra will
come Tuesday PM with the arrival of a cold front.

There is some uncertainty with regards to how fast the cold
front clears Eastern PA Wednesday, so retaining the chance
showers that day. However, the latest ENS and GEFS currently
support a return to drier, more seasonable weather for midweek.

&&

.AVIATION /10Z THURSDAY THROUGH MONDAY/...
A few showers have developed across the northern tier and will
continue to push eastward over the next few hours. Showers and
thunderstorms are struggling to develop and are not as
widespread tonight as originally anticipated across the northern
tier of the state. It`s possible some early morning showers
could develop across the south as a local vorticity maxima moves
across southern PA.

Ceilings will gradually lower at BFD as throughout the overnight
and early morning hours. A period of MVFR ceilings is likely
after 06Z with IFR ceilings expected after 09Z. There is fairly
high confidence that the low clouds extend down to JST with the
HREF showing a 60-70% chance of MVFR ceilings there. Elsewhere,
VFR conditions are anticipated.

As the front progresses through the area during the afternoon
today, thunderstorms will become more focused across the south.
While all sites will likely see showers at some point during
the TAF period, the exact timing of thunder will have to be
adjusted in the forecast once we have a better idea of the exact
placement of storms. Brief visibility restrictions and gusty
winds will be possible in any of the stronger thunderstorms. A
majority of the convective activity will be out of the region by
03Z tomorrow.

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...Banghoff
NEAR TERM...Banghoff
SHORT TERM...Fitzgerald/Banghoff
LONG TERM...Fitzgerald
AVIATION...Bauco/Bowen