473
FXUS61 KPBZ 111202
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
802 AM EDT Mon May 11 2026

.WHAT HAS CHANGED...
Frost/freeze headlines continue.

&&

.KEY MESSAGES...
1) Frost chances continue through daybreak north of Pittsburgh.
A widespread frost/freeze likely tonight.

2) Rain chances persist Wednesday morning through Thursday. Low
rain/storm chances return for the weekend.

&&

.DISCUSSION...
KEY MESSAGE 1...
High clouds continue to stream across the area, departing from
east to west this morning. While these may slightly limit
radiative cooling in the early morning hours, calm conditions
may still be enough to allow for patchy frost this morning north
of Pittsburgh, most likely in the I-80 corridor (>50%). Should
temperatures preform towards the lower end of HREF guidance
(10th percentile), there is a low probability of an areal frost
as far south as US-22, and a freeze possible for the I-80
corridor. But, in reality, much of the temperatures will be
terrain driven, with sheltered non- river valleys performing
towards the 10th percentile with cold air drainage, while other
areas will be closer to the 25th to 50th percentile
temperatures. Nonetheless, the frost advisory attempted to
capture areas where an areal frost is "most likely", though
temperatures may vary.

Tonight, there is high confidence in even clearer and calmer
conditions right under high pressure which will lend to even
more effective radiative cooling. This maintains a >50% chance
of a frost area-wide, with a freeze "most likely" (>50%) for
areas within the freeze watch along the I-80 corridor and
eastern Tucker County. However, there it at least a >25% chance
of a freeze anywhere. The coolest drainages and small valleys
even carry the lower-end chance of a hard freeze, so
agricultural partners should be advised. In summary, freeze
conditions will have to be monitored through today to see how
the frost advisories and freeze warnings actually pan out.
Additionally, in coordination with neighboring offices, the
watch was held as to not have multiple headlines in effect with
different information and calls to action. Tonight`s threat will
be assessed after the frost advisory expires.

KEY MESSAGE 2...
Despite perhaps a low-end chance of a isolated shower in
shallow daytime cumulus today, the next chance for rain will
come Tuesday night into Wednesday. Ensemble cluster have come
into more agreement with a deeper, passing longwave trough.
This, in turn, develops an occluding surface low over the Great
Lakes. Decaying convection from the day prior will lead off rain
chances early Wednesday morning in eastern Ohio. Saturated and
moist adiabatic profiles may promote efficient rain processes
with most likely rain totals before 2pm Wednesday of up to 0.5",
most likely for the I-80 corridor, with amounts decreasing to
the south, farthest from forcing. High end rain totals of 0.75"
to 1" are only possible in the I-80 corridor in the low-
probability event rainfall remains convective along the warm
front. In any event, flood concerns are low to none.

Into the late morning and early afternoon, there is increasing
confidence that the area will be embedded in a narrow warm
sector as a triple point low forms near Lake Erie.
Conventionally, this type of set- up would at least bring low-
end severe chances before and along the cold front passage (with
30kts to 45kts of shear between the surface and 500mb), but
chances will depend on the environment within that warm sector.
In the more likely event that the warm sector remains cloud and
rain-laden, instability would be <250 J/kg and would not
support robust convection In the lower probability event of
clearing, instability generation could reach up to 1000-1500
J/kg as evidenced by LREF 90th+ percentiles. For now, CSU ML and
CIPS has the highest threat to the east, and NCAR ML has the
biggest threat to the south (along with the highest chances of
clearing, respectively), but this will need to be monitored.

Chances have increased for non-hazardous showers Thursday with
shortwave enhancement under a cold-core upper low. Into the
weekend, the main uncertainty is if the upper low cuts off from
the flow and lingers or remains within the flow and allows
ridging to progress faster. A more progressive trough leans
towards ridging, a warming trend, and storm chances for next
weekend. A slower trough departure would tend be slower-to-warm-up
and drier, comparatively.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
VFR prevails through the 24-hr TAF period as surface high
pressure builds across the region. A crossing upper trough may
support a scattered to occasionally broken cu/stratocu deck in
the afternoon, but cigs remain VFR around 5-7kft. Deeper mixing
will result in NW winds gusting up to 20kt starting in the late
morning. Gusts diminish after 00z and light/variable winds and
clearing skies prevail overnight.

Outlook...
VFR should continue Tuesday under high pressure. Tuesday
evening, a broken cloud deck will be moving in from the
northwest with ceilings remaining VFR until the overnight hours.
Showers and restrictions return Tuesday night through Wednesday
night with crossing low pressure. VFR returns Thursday and
Friday under high pressure.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Freeze Watch from late tonight through Tuesday morning for
     PAZ007>009-013>016-022-077-078.
OH...None.
WV...Freeze Watch from late tonight through Tuesday morning for
     WVZ514.

&&

$$

DISCUSSION...Milcarek
AVIATION...Cermak/Lupo