298
FXUS61 KPBZ 201756
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
156 PM EDT Sun Sep 20 2026

.WHAT HAS CHANGED...
A Flood Watch has been issued for areas near and south of
Pittsburgh through noon Monday, as there is a bit higher
confidence in potential excessive rainfall. No major changes to
the expectations regarding the overall pattern. Also updated
aviation section with 18z TAF package.

&&

.KEY MESSAGES...
1) Rain chances continue into the midweek period. Longer
duration rainfall totals could be high and lead to localized
flooding and/or river rises.

2) Much cooler temperatures arrive by mid-week.

&&

.DISCUSSION...
KEY MESSAGE 1...
There has been little change to the thinking regarding the
large-scale pattern. An approaching mid-level ridge is progged
to flatten as it crosses the Great Lakes tonight and tomorrow
morning. Meanwhile an Upper Plains shortwave trough will meander
eastward with time, eventually digging into the Middle Ohio
Valley by midweek. This keeps a favorable storm track across our
region into at least midweek, with periods of quasi-zonal flow
supporting mid-level disturbances tracking across the Upper Ohio
Valley.

After a few morning rounds of heavy rain in eastern Ohio and
southwest Pennsylvania, lighter rain from a decaying MCS will
track across the region through the early afternoon. This should
not exacerbate any local flooding concerns initially. With a
stationary boundary draped across the region which will nudge
southward towards the Mason-Dixon line this evening, deeper
instability (also inhibited by abundant cloud cover) should
remain mainly south of the region, largely mitigating any severe
risks.

That said, deep and anomalous moisture (PBZ 12Z PWAT of 1.92
inches represents a September 20th climatologic record) will be
maintained into Monday, especially from Pittsburgh on south.
While a relative lull in activity is pictured during the very
late afternoon/evening hours, the next vort max/ripple
(currently near Chicago) is expected to approach our area after
midnight and cross through Monday morning. HREF means suggest
0.5 to 1.5 inches is possible near and south of Pittsburgh from
this round (24 hour total through 06Z Tuesday), but maximum
fields suggest several stripes of 2 to 3 inches is possible -
certainly reasonable given the high PWAT and nearly saturated
soundings. Given the very saturated ground already in place, a
Flood Watch for flash flooding has already been issued for this
area through noon Monday. The exact placement of the heaviest
totals remains a bit uncertain, and will depend on the progress
of the front as well as other mesoscale details.

CAMS then suggest another general lull Monday afternoon into the
evening, and this is why the Flood Watch only extends through
noon Monday for now. The pattern thereafter suggests additional
rounds of rain, as noted above. Decreasing precipitable water
values with time and very muted instability levels suggest a
lesser threat of flash flooding with time. However, long-
duration, lighter rain may still support more of a overflow
flooding/river flooding risk into the midweek period. NBM
48-hour rain totals through 8 PM Wednesday still suggest the
potential for 1-2 inches of rain southeast of a DUJ/PIT/PKB
line. Again, the location of highest totals may depend on the
fate of the slow-moving frontal boundary that will be hovering
near the WV/PA border. In any case, flood threats will be
maintained through at least Wednesday. Some showers may even
linger into Thursday as the main approaching trough possibly
closes off into an upper low. There is still hope for a drier
pattern for Friday and next weekend.


KEY MESSAGE 2...
Cool temperatures remain the second part of the story this week.
Given the abundant cloud cover and stubborn east/northeast flow,
higher ridge locations may have trouble reaching 60 degrees
Tuesday through Thursday, while lower and mid 60s will be common
west of the higher elevations. While minimum temperatures will
remain fairly close to normal, daytime highs may run some 10
degrees below climatology during the midweek period.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
MVFR to IFR ceilings have not improved much this afternoon but
still have a few more hours to tweak past 1,000 feet before 00z.
most sites will be ifr overnight and early Monday (Probability of
LIFR is roughly 20-30% tonight before slightly drier air starts
to work into area on northeast winds).

Ceilings should creep back up to MVFR later Monday morning as
northeast winds gust to 20 knots and mixing slightly drier low
level air.

Areas south of PIT will be wettest over the next 24 hours with
rounds of showers continuing tonight into Monday. Thunderstorm
chances will be highest at ZZV HLG MGW and least over the
northern airports.

Outlook... Restrictions will likely continue into Tuesday and
perhaps Wednesday with sufficient boundary layer moisture
impacting low level clouds.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch through Monday morning for PAZ020-021-029-031-
     073>076.
OH...Flood Watch through Monday morning for OHZ039>041-048>050-
     057>059-068-069.
WV...Flood Watch through Monday morning for WVZ001>004-012-021-
     509>514.

&&

$$

DISCUSSION...CL
AVIATION...Craven