309
FXUS61 KPBZ 112323
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
723 PM EDT Mon May 11 2026

.WHAT HAS CHANGED...
There is a bit less confidence in the development of frost south
of I-70 and away from the terrain tonight. Frost/freeze
headlines have been issued in other locations. Potential for
strong to severe thunderstorms on Wednesday has increased
slightly.

&&

.KEY MESSAGES...
1) Widespread frost/freeze conditions are expected north of I-70
tonight, with spottier frost to the south.

2) Rain chances persist Wednesday morning through Thursday, with
a low-end potential for severe storms Wednesday afternoon. Low
rain/storm chances return for the weekend.

&&

.DISCUSSION...
KEY MESSAGE 1...
Afternoon cumulus are forecast to largely collapse by sunset.
Surface high pressure tracking just north of the region, across
the eastern Great Lakes, will result in light wind and mostly
clear conditions initially this evening. However, overnight,
some mid-level warm advection and moisture may lead to at
least patchy clouds crossing overnight, especially south of
I-70. This reduces confidence in the development of anything
beyond patchy frost in this area. To the north, there remains
relatively higher confidence of frost/freeze conditions. The
HREF shows 50% or greater chance of temps 36 degrees or colder
north of I-70 and in the deeper valleys to the east, with
generally 40 to 60 percent chance of freezing temperatures in
the Freeze Watch area. Thus, have converted the Watch to a
Freeze Warning, and have added a Frost Advisory generally south
to I-70. Patchy frost is still possible in areas without
headlines, and the coolest drainages and small valleys even
carry the lower-end chance of a hard freeze.

KEY MESSAGE 2...
Models are in good agreement on dropping the next shortwave
trough axis across the central Great Lakes by 12Z Wednesday, and
then moving it across the Upper Ohio Valley on Thursday. An
associated occluding surface low will accompany this system. A
closed 500mb low is then likely to develop and drift across the
northeast CONUS. Cluster analysis shows some minor disagreement
on how quickly this upper low departs as it moves off of the New
England coast either Friday or Friday night.

Rain returns first to eastern Ohio Wednesday morning as earlier
convection to the west continues to decay. This general area of
rain should then pull east across the region during the morning.
After a brief, narrow warm sector, some additional convective
development is expected ahead of the afternoon cold frontal
passage. Despite copious lift provided by the shortwave and
front, precipitable water values will likely top out in the 0.9
to 1.1 inch range (25th/75th ensemble percentiles). This will
keep a cap on heavy rain potential, even in the more vigorous
afternoon convection scenarios. Probabilities of 48-hour
rainfall totals (through 00Z Friday) of an inch or more top out
in the 30 to 40 percent range north of I-80. Most-likely total
QPF across the area ranges from 0.40 to 0.80 inch. Thus,
flooding threats are inconsequential.

The main question then becomes the potential for severe
thunderstorms Wednesday as that narrow warm sector passes. The
amount of clearing of clouds and rain will be key to the amount
of destabilization that can occur. In the event of a "dirtier"
warm sector, MUCAPE of 500 J/kg or less would be likely, keeping
the severe threat lower. More clearing/a bit of sunshine could
lead to 1000+ J/kg of buoyancy that would lead to better severe
chances. Isolated damaging wind gusts would be most likely in
this latter scenario. NCAR convective machine-learning guidance
matches well with the SPC day 3 marginal (level 1 of 5) risk for
severe thunderstorms south of US-422. CSU guidance suggests the
main risk east of the Laurels, which would be reasonable in the
lower CAPE scenario. Additional clarity on severe potential
should occur when the event enters the window of CAM guidance.

Showers are likely to linger at least through Thursday with the
crossing upper low, but the end time of these will depend on the
uncertainty noted above regarding the low`s departure. A slower
departure would lead to a slower warmup Friday and into early
next week, while a more progressive solution would bring a
quicker return of showers (as early as Friday night) as well as
a faster above-normal temperature trend. In any case, there is
increasing confidence in an overall, lasting pattern flip
towards above-normal temperatures as we progress through May.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
High confidence VFR prevails through the 30hr extended TAF
window. Gusts are expected to abate here over the next hour,
yielding light and variable winds.

High pressure centered across the region tomorrow promotes
light SSWerly winds with largely clear skies. Mid-level clouds
increase in coverage late Tuesday ahead of our next low pressure
system.

Outlook...
Restrictions return with showers Tuesday night through Wednesday
night with crossing low pressure. VFR returns Thursday and Friday
under high pressure.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Frost Advisory from midnight tonight to 8 AM EDT Tuesday for
     PAZ020-021-029-073>076.
     Freeze Warning from midnight tonight to 8 AM EDT Tuesday for
     PAZ007>009-013>016-022-077-078.
OH...Frost Advisory from midnight tonight to 8 AM EDT Tuesday for
     OHZ039>041-048>050.
WV...Frost Advisory from midnight tonight to 8 AM EDT Tuesday for
     WVZ001>003-510>513.
     Freeze Warning from midnight tonight to 8 AM EDT Tuesday for
     WVZ514.

&&

$$

DISCUSSION...CL
AVIATION...Lupo/AK