-- Discussion containing changed information from previous version are highlighted. --
327
FXUS61 KCTP 261930
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
330 PM EDT Sun May 26 2024

.SYNOPSIS...
Weak high pressure will reside overhead today. A warm front over
the Southwest corner of PA will lift across the much of the
state early tonight, but will likely stall its progress near or
just to the east of the Susquehanna Valley until later Monday.

Low pressure will pass over the Upper Great Lakes on Memorial
Day, dragging a cold front through late Monday/evening. An upper
level trough will build into the region for the remaining
portion of the week.

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...
Earlier clouds and morning fog hung tough in some areas until
around the noon hour, but now we see abundant sunshine, warm
temps and similar to Saturday, moderately high dewpoints in the
60s (making it feel a bit muggy) across Central and Southern PA.
Vertical mixing has tapped into an east/west band of much drier
air aloft (around the 900-850 mb level) and caused sfc
dewpoints to dip into the more comfortable mid 50s across the
Northern Mtns of PA.

Sfc warm front over SW PA at 18Z will push NE late this
afternoon and this evening ahead of a sharp/neg tilt mid level
trough. A few pulse type late afternoon TSRA could develop near
this boundary as a result of enhanced llvl convergence and high
level heating across the ridges of the Laurels.

A layer of slightly milder air from 8-12kft over the area and a
veil of cirrus spreading in from the west during the mid to
late afternoon should cap off deep convection elsewhere.

Max temps will reach the u70s on top the nrn mtns and the
Laurel mtns, but 80s elsewhere.

&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM MONDAY/...
-- Changed Discussion --
A tongue of moderately high CAPE (with 0-1km ML values of
1400-2000 j/kg near and to the south of I-80 in Central and
Western PA) just ahead of the aforementioned mid level trough
axis will combine with increasing low-level southerly flow to
support an area of potentially strong to SVR TSRA across mainly
the SW half of the CWA this evening.

POPS ramp up quickly to Likely-Categorical with this feature
this evening. Leading edge of the TSRA (moving NE from the
Middle Ohio River Valley at 42KTS) arrives across the Laurel
Highlands shortly before 00Z Monday and impacts the Central Mtns
of PA between 01-03Z.

Some fog may again form early tonight. But the invading and
thickening clouds and showers/storms due to the first of a few
pre-frontal troughs will probably preclude the fog from becoming
too thick or widespread, and the precip may actually bring the
visby back up if it does initially go down within any fleeting
clear spots.

The forcing tonight likely makes a long band of showers/storms
cross the area from SW-NE in the evening and first half of the
night. More nebulous forcing then exists for 3-6hrs before the
next wave of forcing moves in from the west.

The late night timing of the second batch of precip will be
associated with less thunder than the initial round, especially
as the LLVL jet and convergence along the initial trough
weakens slightly with the winds veering a bit to the SSW.

That precip will still be crossing the eastern half of the area
in the morning/daylight hours. This could stabilize things for
the first part of the afternoon there. But, the west will likely
have enough breaks in the clouds and moisture to be able to
cook up good CAPE for the early aftn, and TSRA will pop up.

This third batch of storms looks to be quite potent and
widespread and will likely to produce some severe wx.
Collaborated with SPC and surrounding WFOS adjacent to the
eastern half of our CWA to extend the SLGT risk north to the
PA/NY border as we see a highly anomalous southerly LLJ of 35-40
kts down to 2 KFT AGL (and close proximity of a sfc warm
frontal boundary to the east) fueling the storms with plenty of
deep layer shear for discrete super-cellular structure within a
low LCL environment. Given these factors (partly the result of
a sub 1000 mb low over SW Ontario) we`ll see 0-1 KM EHIs of 3-4
m2/s2 near and to the east of the Susq Valley and a SPC 5% TOR
risk, with CAPE peaking <=2000J. Main threat is wind, but 1"
hail also a threat.

PWAT goes above 1.5" (approaching 2") in the eastern half of
the area in the late morning and aftn hours. The repeated shots
of rain will lead to a risk of flash flooding over much of the
area on Monday, but mainly in the east in the aftn. The strong
surface low will move northeast across the Upper Great Lakes and
into ONT. Two pushes of drier air and a gradual veer to the
wind is expected in the evening and overnight.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Once any lingering showers/storms pull east of the area Monday
evening, drier air will begin to filter in behind the departing
front.

Medium range guidance continues to point to a period of cool
weather Tuesday through Thursday, as a deep upper level trough
pivots southeastward from the Great Lakes. Cold temps aloft
should support a daily chance of diurnally-driven
showers/storms, with the highest POPs across the elevated heat
source of the Allegheny Plateau. The best overall chance of
showers should come with the passage of a strong shortwave
on Wednesday.

We should see a transition to drier and warmer weather Friday
into Saturday, as the upper level trough axis shifts east of PA
and high pressure builds into the region. An approaching frontal
system could bring our next round of showers/storms by next
Sunday.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
Shrinking areas of IFR/MVFR in the Central Valleys and Middle
Susq Region late this morning will quickly transition to VFR
in all areas by 17Z with VFR conditions prevailing throughout
the rest of the daylight hours. Winds will be range from
5-10kts during the afternoon/early evening with gusts upwards
of 15kts along ridgetop locations.

Included a several hour or longer period of LLWS at all TAF
sites later this evening into at least the late morning hours
Monday.

Guidance suggests SHRA/TSRA entering the southwestern periphery
of the area near 00Z Monday and overspreading the entire area
through 12Z. Generally low-end VFR to high-end MVFR conds are
expected with some potential for localized restrictions.
Guidance has started to suggest some timing of localized
restrictions, but given low (~20%) confidence and little
temporal continuity in guidance runs, have opted to keep these
restrictions minimal in this TAF package.

Conds will continue to trend towards MVFR/IFR conds near and
after 06Z. There is some concern for a return to LIFR/IFR conds
overnight tomorrow night across eastern PA where some hints
towards enhanced low-level moisture, but have opted to keep
these concerns out of the TAFs until further model consistency
is achieved.

Outlook...

Mon... Persistent restrictions are expected in widespread
showers and thunderstorms.

Tue-Wed...Brief restrictions are possible in scattered showers,
but much of the time should be VFR.

Thu...Predominantly VFR.

&&

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

&&

$$

SYNOPSIS...Lambert/Dangelo
NEAR TERM...Lambert/Dangelo
SHORT TERM...Lambert/Dangelo
LONG TERM...Fitzgerald/Evanego
AVIATION...Lambert/NPB