981
FXUS61 KCTP 290031
AFDCTP

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

.SYNOPSIS...
*Heat and humidity spike fuels severe T-storm risk this weekend
*Refreshing/dry start to July; heat+T-storms return by the 4th

&&

.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/...
Roller coaster of conditions will continue in the long term.
After a comfortable summer day on Tuesday, temps and humidity
hit the big first hill climb. Risk of Heat Index values
eclipsing 100F is there for the SE/Lower Susq on Thurs. Air
temps should be >90F for each day Wed-Fri as big Bermuda high
noses all the way to the MS River. The return flow from the
GOMEX will make it soupy and min temps may not dip past 70F in
many places in the middle of the week. Model/WPC guidance hangs
a front up just to our N and keeps us in the warm sector. Daily
30-50 PoPs already in the forecast will be held onto. If you
like South Carolina in the summer, you`ll love the middle of
next week here.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Wind will stay up overnight out of the S/Se for most terminals.
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 and
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...Steinbugl
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...Dangelo
AVIATION...Dangelo
CLIMATE...Steinbugl