559
FXUS61 KCTP 280249
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1049 PM EDT Thu Jun 27 2024

.SYNOPSIS...
*Seasonable end to the week with comfortable humidity
*Return of heat+humidity fuels T-storms this weekend
*Cooler & dry start to July; heat & T-storms by the 4th

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
645 pm update... The diurnal cumulus field is fading fast this
evening with the loss of daytime heating in a dry air mass. This
will lead to a clear and refreshingly cool night for late June.

As indicated in the previous discussion, good radiational
cooling conditions overnight should lead to the development of
river valley fog, especially across northern PA and across the
Alleghenies. Lows by daybreak will range from the mid 40s across
the northern tier, to the upper 50s over portions of south-
central PA.

Previous discussion... Cu will crumble this evening setting up
a refreshingly cool and mainly clear night across central PA.
Low pwats and favorable radiational cooling pattern supports
trending below the 50th percentile NBM with relatively chilly
min temps in the mid 40s across the northern tier. Beneath dome
of 1020mb high pressure, synoptic conditions support fog
formation late tonight into early Friday morning in the
river/stream valleys across the western and northern
Alleghenies.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
AM fog will dissipate quickly after sunrise Friday. Expect
partly cloudy and seasonably comfortable conditions with highs
75-85F.

An increasingly strong southerly llvl return flow develops into
Friday night as the aforementioned surface high shifts eastward
off the New England coast. Latest model data suggests 30-40kt
LLJ from the south-southwest will drive some showers and
elevated t-storms over west central PA late Friday night into
early Saturday morning.

The belt of strong 850mb flow will transport rich low level
moisture (dewpoints in the upper 60s to lower 70s) northeastward
along/ahead of a cold front this weekend. PWAT values are
forecast to reach 1.5-2.5 inches on Saturday or +2-3SD. The
anomalous deep layer moisture will support risk of heavy to
potentially excessive rainfall. WPC currently has a broad MRGL
risk, but the setup will likely yield an upgrade to SLGT risk
particularly where FFGs are reduced. Although mid lvl lapse
rates may remain weak, high dewpoints and diurnal heating should
fuel at least moderate buoyancy by mid/late afternoon. The
projected instability and deep shear profiles support a
conditional risk of strong to severe storms. SPC has most of the
area in a MRGL risk for D3, but their discussion suggests a
categorical upgrade/expansion of SLGT risk (just to the west) is
possible in subsequent outlooks. The influence of early day
clouds/waning overnight convection could be a limiting factor.
Convection should decrease in coverage and intensity into
Saturday night, which will be warm and muggy with lows 65-75.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
On the large-scale, a fairly zonal upper-level flow pattern
will stay in tact over the northern tier of states next week,
with energetic short-waves traversing this flow every 3-4 days
or so. Consequently, expansive summertime upper ridging will
largely stay south of PA, keeping excessive heat mainly out of
the forecast for the time being.

Looking at the daily sensible weather, as one of the above
mentioned short-waves presses through eastern Canada and New
England early next week, it will push a surface cold front well
to the southeast of the Commonwealth, bringing another stretch
of dry conditions and comfortable temperatures/humidity levels
for Monday and Tuesday. Confidence in this scenario is
relatively high.

By the middle of next week, as a surface high pushes offshore
and heights aloft begin to build, summertime heat and humidity
should at least temporarily make a run at PA. At the same time,
though, the next upstream surface cold front and upper-level
trough will be approaching from the northwest. The most likely
scenario here is for increasingly muggy conditions and higher
chances for showers and thunderstorms. Just how hot temperatures
are able to get, or robust convection becomes, is fairly
uncertain. Better knowledge of these factors will require
considerably more time and additional model runs to see how
atmospheric features resolve themselves during this time frame.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Late evening update.

Main change was to adjust winds to the north, based on current
obs and guidance.

Earlier discussion below.

For the 00Z TAF package, looking at mainly clear skies
overnight, as high pressure builds into the area.

As I mentioned on the late afternoon update, I added a TEMPO
group for fog at BFD late, as low temperatures drop to or just
below the expected dewpoint.

Friday looks like a dry day at this point, with a southerly
flow of air and just a few clouds.

More in the way of adverse weather for the weekend, as a warm
front lifts northward, followed by a cold front on Sunday.

Outlook...

Sat-Sun...Widespread showers and thunderstorm with impacts
possible.

Mon-Tue...Dry weather with VFR conditions.

&&

.CLIMATE...
Through 6/26, June ranks as tied for the second warmest on
record at Harrisburg.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Jurewicz/Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Jurewicz/Steinbugl
AVIATION...Martin
CLIMATE...Steinbugl