540
FXUS61 KCTP 290325
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1125 PM EDT Fri Jun 28 2024

.SYNOPSIS...
Low pressure will track north of Pennsylvania this weekend, with
the attendant warm front lifting through the state Saturday and
the trailing cold front coming through Sunday. A large high
pressure system will build into the region early next week,
then a dying cold front will likely push in from the Great
Lakes and stall out over the area late next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A building low amplitude upper ridge over the Mid Atlantic
region should provide most of Central PA with dry and mild
conditions overnight. However, a weak shortwave approaching from
the Upper Midwest will bring the chance of late night showers
across the northwest part of the forecast area. A developing
southwesterly low level jet and surging pwats ahead of the
shortwave will overrun a slow-moving warm front over Western PA,
bringing the best chance of showers and a slight chance of tsra
to the N Mtns between 06Z-10Z.

High pressure passing off of the New England coast will result
in an increasingly moist low level southeast flow across the
region overnight, likely resulting in developing stratus,
especially where the flow is forced to ascend the higher terrain
of Central PA. The increasing cloud cover/low level moisture,
combined with an active south-southeast breeze, will result in
much warmer conditions than last night with min temps in the
60s.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
A low amplitude upper trough will approach from the Grt Lks
this weekend, with the associated surface low passing well north
of PA through Southern Ontario/Quebec. The attendant warm front
is progged to lift through Central PA Sat PM and the trailing
cold front should slice southeast across the forecast area
during the daylight hours of Sunday.

GEFS pwats surge to +3SD above climo Saturday, as the warm front
works into the region. Diurnal heating of the moist and
increasingly unstable airmass along and west of the advancing
warm front, combined with a belt of 50kt mid level flow across
Northern PA, should set the stage for the potential of strong to
severe thunderstorms during the afternoon and evening hours.
Convection-allowing model guidance indicates the focus of the
showers/tsra will be across the NW Mtns during the morning and
early afternoon, then expand into the southeast part of the
forecast area during the PM hours, as the upper trough and plume
of highest pwats shifts east.

Model soundings indicate there will be a good deal of
cloudiness Saturday, especially over the north-central
mountains, where model RH profiles indicate stratus could linger
into the early afternoon ahead of the approaching warm front.
However, even modest diurnal heating should yield capes in the
neighborhood of 1000 J/kg Sat afternoon per latest ensemble
output. The moderate instability, combined with progged 0-6km
shear of 40-50kts, is more than sufficient to support organized
strong/severe convection Sat PM with a few supercells and an
isolated tornado possible, especially across the northwest half
of the forecast area, where HREF UHEL values are highest and STP
values peak near 2.

The unstable environment,paired with anomalous pwats, suggests
locally excessive rainfall/flash flooding is also possible Sat
PM. The area of most concern is across the N Mtns, where FFG
values are lowest and where latest HREF supports localized
amounts of 3-4 inches. If 00Z guidance remains bullish over
Northern PA, a short fused FF watch may be needed. Much higher
FFGs will be a limiting factor to reduce the flood risk farther
to the south and east across the CWA (where D0 and D1 drought
conditions exist).

Latest model guidance indicates the bulk of the convection will
shift east of the region late Sat night, as the lead shortwave
and plume of highest pwats exit the state. However, passage of
the surface cold front will bring the chance for another round
of convection Sunday. Locations most likely to see potential
strong/svr t-storms are over the southeastern part of the CWA
due to a fropa coinciding with peak heating of the late afternoon.

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/...
A fair and cool Monday night looks likely as high pressure and
associated dry airmass build directly over PA, resulting in
efficient radiational cooling and min temps several degrees
below normal. Fair and warmer weather is expected Tuesday into
at least the first half of Wednesday, as upper level ridging
builds over the state and surface high drifts offshore.

All medium range guidance tracks a weakening shortwave well
north of PA late Wednesday into Thursday. The dying cold front
is likely to sag into the state Thursday and stall out in the
vicinity of PA through Friday. Falling heights/surging low level
moisture ahead of the front could support scattered convection
as early as Wednesday afternoon over the northwest half of PA.
However, a better chance of showers/tsra areawide will come
with the arrival of the front Thu into Friday. Early best guess
of late week rainfall based on ensemble plumes ranges from 0.25
to 0.75 inches, with the highest amounts over the N Mtns and
least in the south.

Heat and humidity should peak ahead of the front Wed-Thu.
Ensemble mean 850mb temps surging to near 20C indicate max temps
could reach the low to perhaps mid 90s in the Lower Susq Valley
Thursday, with high humidity pushing heat indices into the mid
and upper 90s. Ensemble plumes suggest slightly cooler daytime
temps late week, due to more clouds/showers. However, high pwats
in the vicinity of the stalling front should result in muggy
nights and above normal min temps the entire second half of next
week.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Wind will stay up overnight out of the S/SE for most terminals
with increasing low-level flow. The LLJet of 40-45KTs rolls up
from S to N over the Alleghenies. 40+KT of LLWS is certain for
BFD and JST. The ceilings will lower to IFR over the east (80pct
chc) as the SE flow brings in very high Atlantic moisture. Over
the west, a warm front should be on the doorstep at 12Z and a
few -SHRA or just plain -RA will start to fall over the NW
third/half of the Central PA airspace after midnight and make
the nrn tier damp/wet by sunrise. Cigs look like they should be
a little higher over the W than E overnight according to MOS and
HREF vsby potential progs.

The low stratus is expected to lift and become broken to
scattered in the morning over the S, and gradually work
northward a bit in the mid-day and aftn. Numerous TS/SHRA will
be popping up over the NWrn third of PA in the morning and
stronger thunderstorms develop later on Saturday. High moisture
will make the potential for very heavy rain and very low vsbys
in the TSRA. TSRA will continue pressing SE thru the evening and
first half of the night Sat night. The chance for showers and
storms will linger across the southeast Sunday as a cold front
drags it`s feet moving through the area. There could be fog Sat
night in the NW (BFD), but that will depend on the amt of
clearing. IFR from overnight/AM fog (Sun morning) at BFD is only
a 40pct chc at this point, and lower elsewhere as not much
clearing is expected elsewhere.

Outlook...

Mon-Tue...Dry weather with VFR conditions except perhaps some AM
valley fog N.

Wed...PM TSRA moving across from W-E.

&&

.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...Fitzgerald
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...Fitzgerald
AVIATION...Dangelo/RXR
CLIMATE...Steinbugl