Tornado Warning 14, NWS Pittsburgh, PA

Area Forecast Discussion
National Weather Service Pittsburgh PA
417 PM EDT Wed May 21 2025

.SYNOPSIS...
Shower and thunderstorm chances continue today as low pressure
lifts north toward the lower Great Lakes. There remains a
flooding threat for portions of the upper Ohio Valley and a
low-end severe risk today. Rain chances will continue into
Thursday with lesser chances by Saturday. However, the upper
trough will keep temperatures below average.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
KEY MESSAGES:

- Flood watch remains in effect through Thursday morning, but
  threat areas seems to be trending closer to the I-80 corridor.
- Tornadic threat waning with storms exiting better environment.
-------------------------------------------------------------------

415pm update...
A line of showers and thunderstorms producing around 1"/hr rates
continues to swing ENE along a prefrontal trough in west central
PA while a trailing line with up to 0.5"/hr rates approaches the
WV/OH border ahead of the cold front. The concern for tornadic
activity (which prompted the watch) due to indicators suggestive
of low-level tilting/stretching are starting to wane as the main
axis of storms exit the favorable region and those parameters
fade.

The focus through this evening will be on the flooding
potential; convergence near the Low triple point is leading to
stalled and/or slow moving storms near the I-80 and I-79
intersection of northwest PA. This region was highlighted by 12z
HREF data as having potential for 3+" accumulation (though low
probability); this result is looking more possible now as rain
gauges in the region show 1 to 2" of accumulation already.
Further monitoring of storm convergence areas (likely favoring
locations near and just south of I-80) will continue through
tonight as the Flood Watch remains in effect.

Rain showers are likely to continue after 10pm tonight amid cold
advection, but the passage of the surface cold front should
limit rainfall rates and scattered areal convection. It is
possible that the flash flood threat would trend downward as
well, but will wait on any watch changes to see impacts seen
from this afternoon's storms.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
KEY MESSAGES:

-Rain showers will persist on through Thursday and Friday.
----------------------------------------------------------------

Low pressure will remain parked over the Great Lakes through the
start of the weekend, gradually shifting eastward into Saturday.
This will keep unsettled weather across the upper Ohio Valley
through the time period with rain chances continuing. Expect
higher coverage in showers Thursday afternoon with the help of
diurnal heating and a general decrease in precipitation into
Friday with the possibility of short-wave ridging drying out the
region outside of the I-80 counties and the ridges where
upslope may allow for showers to persist.

Subsidence increases area wide on Saturday but northwest flow
may still lead to a few showers lingering over the northern
counties, though chances are lowest by this time.

Cold advection will keep temperatures well below seasonal
averages through the period - with highs barely hitting 60 when
we should be in the 70's in late May.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
KEY MESSAGES:

- Continued daily rain chances into the weekend.
- Moderating temperatures but still below normal.
-------------------------------------------------------------------

A series of shortwaves will traverse the broad upper low bringing
enhanced periods of rainfall into the weekend. Ensembles continue to
show slight differences in speed of low pressure departure,
impacting shower chances on Saturday. Building high pressure to our
south may begin to win out on Sunday and some solutions suggest just
some upslope driven showers, but confidence still remains low.
Despite some moderation, temperatures are still favored to hold
below normal. Continued low confidence for Monday for precip
potential is expected as most models stall the exiting front and
some push the front through. Thus will leave low chance precip probs
in from Monday and most of Tuesday as well as temperatures try
to make a return to normal.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
A cold front will cross the area with ample forcing for storm
development. The instability gets more questionable north and
east of Pittsburgh, hence, PROB30s were issued for FKL and DUJ.
Tempos were issued for the other terminals based on the timing
of the storms. These storms could put down temporarily strong
gusts, generally from a southwesterly direction, but should be
confined to the front itself.

Drier air aloft makes its way in behind the front temporarily
in upper subsidence allowing ZZV, HLG, and MGW a brief break
from ceiling restrictions during that time. PIT and AGC have a
moderate chance to see a brief window of VFR ceilings. Another
shortwave of shallow instability and northwest flow aloft
invigorates more showers into the evening and overnight hours as
surface winds veer more southwesterly. Chances of IFR cigs Wed
night are generally >40% for now across a majority of the region
aside from ZZV/MGW.

Periods of rain and restrictions (mostly IFR) are expected to
continue through Thursday.

Outlook...
Periods of rain and restrictions (mostly MVFR) are expected to
continue on Friday as surface low pressure moves across the
region. Conditions are expected to become drier on Saturday with
the chance of ceiling restrictions lifting mainly south of PIT.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch through late tonight for PAZ021-029-031-073>076.
OH...None.
WV...Flood Watch through late tonight for WVZ021-509>514.

&&

SYNOPSIS...34
NEAR TERM...Frazier
SHORT TERM...34
LONG TERM...Shallenberger
AVIATION...Lupo

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