420
FXUS61 KCTP 050001
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
801 PM EDT Tue Jun 4 2024

.SYNOPSIS...
*Today is the warmest day of the week with a stray shower or
 thunderstorm possible across southern PA.
*Cloudy and humid with showers and thunderstorms Wednesday into
 Thursday capable of producing heavy downpours.
*Cooler/more comfortable stretch Fri-Sun with passing showers
 and storms each afternoon.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Mostly sunny and very warm today (warmest day of the week) with
highs in the 80-90F range or +5-15 degrees above early June
climo. Fair weather cumulus clouds are scattered around the
region today with tranquil conditions characteristic of high
pressure overhead. Sinking air underneath a persistent area of
high pressure has led to deteriorating air quality conditions
(near ground ozone) in southeast PA today. In collaboration with
the PA Department of Environmental Protection, we issued an Air
Quality Alert through 11PM for a few counties in the Lower
Susquehanna Valley to highlight reduced air quality and
encourage sensitive groups to avoid strenuous activity and
outdoor exercise.

The aforementioned ridge of high pressure over Central PA will
also help to maintain dry wx in most locations this afternoon
and evening. A few showers/storms have developed in extreme
southwest PA this afternoon and diurnal heating could help a few
additional storms break through the subsidence inversion across
portions of southern PA. Latest HREF suggests the best chance
of a stray pulse type shower/t-storm will be along the southern
tier ridges into WV/MD panhandle where pwats ramp to 1-1.3 in.

An increasingly moist (higher pwats & dewpoints) southeast flow
ahead of an upstream warm front over the Ohio Valley will send
POPs on a upward trend from late tonight into Wednesday morning.
Expect a muggy overnight with fairly uniform min temps in the
60-65F range (+10-15F above climo) with low stratus and patchy
fog developing over the majority of CPA/east of the Allegheny
Front by daybreak.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Latest suite of hi-resolution guidance expands coverage of
showers Wednesday morning through Wednesday afternoon with max
POPs occurring Wednesday night into early Thursday morning.
Multiple rounds of showers and storms appear likely with this
system. The best chance for severe weather should be confined to
northwest PA where the best combination of ingredients exist,
while farther southeast, persistent southeast flow sets up a
classic "cool" air damming scenario that should limit
instability for much of the day. Persistent low clouds and
southeast wind favor cooler max temps Wednesday (5-10 deg lower
than today) with highs in the 70-80F range.

The bigger threat with this system may end up being the
potential for heavy rainfall and some flash flooding. PWs climb
to 1.25-2.00 inches by 00Z Thu, which favors potential for
locally heavy rainfall. 12Z HREF paints some spot amounts of
2-3" in southern PA while the mean is closer to 0.75-1.5". WPC
upgraded the MRGL Excessive Rainfall outlook to a SLGT for
portions of West Virginia, Maryland, and southwest PA, which
includes Somerset County. Farther east, 3-hr flash flood
guidance in southern PA is 4"+, which would indicate that
flooding is rather unlikely there. The MRGL in effect for the
rest of our area covers the potential for locally heavy
downpours and isolated ponding on roadways in the strongest
showers and storms.

Model consensus shows QPF max shifting to the east Thursday
morning as the frontal system moves across PA. The remainder of
Thursday should feature scattered showers/PM t-storm as upper
low and cooler temps aloft begin to impinge on the area. Most of
this activity will be diurnally driven with little to no precip
expected Thursday night. Post frontal westerly/downslope flow
along with breaks of sun in the dry slot should push temps back
up on Thursday with highs peaking in the mid 80s in the Lower
Susq Valley.

By Friday, the upper low parks overhead and will stick around
into the weekend. Cold temperatures aloft will support
sufficient instability for diurnally driven showers and storms
that are scattered in nature. Dewpoints in the low 50s and
temperatures in the mid 60s to near 80 will feel great after a
very brief glimpse of summer.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
The main weather feature for Central PA through next weekend
will be a slow-moving upper low, tracking from the eastern
Great Lakes across southern Ontario and Quebec. As a result, at
least hit and miss showers and possible thunderstorms are
expected on a daily basis, with diurnally more numerous coverage
anticipated in the afternoon and early evening hours,
particularly for the northern tier of the Commonwealth.

Current indications are that by the end of the weekend into
early next week, the upper tough becomes positively tilted and
the low may retrograde slightly and stall over the great lakes
region. This will continue the unsettled pattern of diurnally
driven showers and thunderstorms through at least Monday
afternoon. Long range ensembles currently show the trough
lifting after Tuesday morning with fewer showers expected as a
result.

Temperatures are likely to average somewhat below climatology
for early to mid-June, with daily highs in the upper 60s and
70s, and overnight lows in the 50s to lower 60s.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
Widespread VFR conditions and light winds are expected the rest
of the evening. However, a moistening southeast flow off of the
Atlantic Ocean will result in developing stratus late tonight
across Central PA. Latest ensemble prob charts indicate the low
cigs will develop between 06Z-11Z with the highest probability
of IFR/LIFR (~70pct) over the Lower Susq Valley (MDT/LNS) and a
lower probability (~50pct) further north and west.

Diurnal heating/mixing is likely to result in rising cigs during
the daylight hours of Wednesday, with mainly MVFR to low IFR
cigs by afternoon based on model soundings. A warm front
lifting out of the Ohio Valley will spread showers and
thunderstorms into the area during the afternoon and evening,
potentially resulting in a brief dip to IFR vsby in a few spots.

The arrival of the warm front Wed evening may result in
improving cigs Wed evening over Southern PA, where predominantly
VFR conditions are likely. However, latest guidance indicates an
upsloping southerly flow ahead of the warm front will likely
result in cigs falling back to IFR over the N Mtns.

Outlook...

Thu...AM showers/low cigs possible, mainly N Mtns. Isolated PM
tsra impacts possible Southeast PA.

Fri...Slight chance of a brief PM shower/vis reduction, mainly
NW Mtns.

Sat...AM low cigs possible NW Mtns. Slight chance of PM
shower/vis reduction NW Mtns.

Sun...Slight chance of a brief PM shower/vis reduction, mainly
NW Mtns.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Air Quality Alert until 11 PM EDT this evening for PAZ057-059-
063-065-066.

&&

$$

SYNOPSIS...Banghoff
NEAR TERM...Banghoff
SHORT TERM...Steinbugl/Banghoff
LONG TERM...Fitzgerald/Bowen
AVIATION...Fitzgerald