073
FXUS61 KCTP 041559
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1159 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/...
A weak, slow-moving and decaying cold front extending from the
Finger Lakes to the NW Mtns of PA will gradually drift south
through this afternoon. HREF indicates that MU CAPE will climb
to between 1000-1500 J/KG across the southern half of PA though
the latest RAP shows pockets of 1800-2300 J/KG sfc-based CAPE
values coincident with areas of more significant clearing late
this morning.

Vertical shear remains quite weak and some layered mid level
clouds will be increasing from the west and overspreading the
NW Mtns and Laurel Highlands this afternoon.

The Central and Lower Susq Valley appears to destabilize the
best today and stand the best chance of SHRA/TSRA, though the
eastward progression of a MCV from the Ohio Valley will also
spread late afternoon/evening showers/embedded TSRA across the
Western Mtns.

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

Still, the combination of instability and marginal shear yields
decent updraft helicity values across the southern tier of the
state, where isolated late day severe weather appears possible.
The presence of +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 /16Z THURSDAY THROUGH MONDAY/...
CIGS have rebounded into the VFR range across all of Central PA
late this morning.

A weak and slow moving cfront draped along a line from near
KELZ to KBFD to KFKL will progress south 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, with the most
likely timing expected to be from the morning to early afternoon
across the north and the mid to late afternoon across the south
east. 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 Friday.
Expect patchy fog to develop across the region overnight tonight
with reductions to visby and cigs likely Friday morning.

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