PBZ issues Area Forecast Discussion (AFD) at May 21, 8:22 PM EDT466
FXUS61 KPBZ 220022
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
822 PM EDT Wed May 21 2025
.SYNOPSIS...
Showers will continue overnight through Friday as low pressure
lifts north toward the lower Great Lakes. There remains a
flooding threat for portions of the upper Ohio Valley into
Thursday morning. Below average temperature is very likely
through the weekend.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
KEY MESSAGES:
- Scattered and occasionally numerous rain showers with
declining flood threat expected overnight.
- A second round of heavy rain over Lawrence/Butler Counties
raises the concern for localized flooding tonight.
-------------------------------------------------------------------
830pm update...
The region has transitioned transition to scattered and
occasionally numerous lighter rain showers as low pressure sits
northwest of the region and cold advection filters in from the
west. Jet ascent and steeper lapse rates will aid a continuation
of the showers but limited instability and lack of forcing
should preclude flooding concerns; thus, the Flood Watch has
been cancelled. There is a caveat as weak convergence across
Lawrence/Butler (PA) counties has aided a band of slower moving
thunderstorms that are showing rainfall rates in the 0.5"-1"
range over areas that already received 2-3" of rain with spotty
flooded road reports. Though it was outside the watch area, this
region will remain a concern over the next 2 hours and is
currently highlighted by a Flash Flood Warning. The HWO will
also highlight these regions and locations north as still having
a non-zero threat for flash flooding overnight.
Overnight temperature will fall with the frontal passage but
excessive cloud cover and residual moisture should keep readings
near the seasonal average.
&&
.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 /00Z THURSDAY THROUGH MONDAY/...
A persistent upper level low over the eastern Great Lakes and
cold advection in a post-frontal environment will aid scattered
to occasionally numerous light rain showers through much of the
TAF period (with a peak in activity likely Thursday afternoon).
Most terminals will begin at VFR but subsidence/cold advection
will foster MVFR to IFR ceilings at most terminals by 06z, with
IFR likely by 12z (save for ZZV/MGW).
The stagnant airmass will offer little ceiling improvement
Thursday amid a continuation of showers, but some mixing may
create occasional breaks to MVFR while fostering gusts to 20kts.
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...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Frazier
NEAR TERM...Frazier
SHORT TERM...34
LONG TERM...Shallenberger
AVIATION...Frazier
Source:
PBZ issues Area Forecast Discussion (AFD) at May 21, 8:22 PM EDT---------------
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