261
FXUS61 KPBZ 211746
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
146 PM EDT Tue Jul 21 2026

.WHAT HAS CHANGED...
Flood Watch has been expanded 1 tier of counties further north.
A Severe Thunderstorm Watch has been issued until 8pm for all
of our OH, WV and PA counties south of a Beaver- Westmoreland
line. Morning rain has soured some of our environment and
shifted our focus a little further south, mainly along the I-70
corridor.

&&

.KEY MESSAGES...
1) Enhanced Risk for severe weather on Tuesday; Slight Risk for
Excessive Rainfall.

&&

.DISCUSSION...
KEY MESSAGE 1...
A large-scale area of low pressure is currently moving through
central Ontario. Remnant showers and storms from overnight
mesoscale convective systems (MCS) continue across the region
early this morning in the unzipping warm sector. Morning
convection has complicated but not eliminated our risk of severe
weather across the region. It has also acted to raise our short
term flood threat.

Our morning sounding only measured a PWAT of 1.32 but continued
moisture advection from our west will look to advect PWATs near
1.9 inches (just below the daily maximum of 1.96 inches) across
the region. This accompanied with a relatively high freezing
level will allow for efficient warm rain processes in a very
moist environment. Instantaneous rainfall rates up to 3-6 inches
per hour seem possible but this will be tempered by shorter
residence time of these rates owing to quick storm motions. With
more progressive storms we have a higher chance of exceeding
our 3 hour flash flood guidance more so than our 1 hour values
likely requiring multiple rounds of storms. Morning rain is
acting to set the table for flood issues later across a wider
portion of the region and thus our Flash Flood Watch has
expanded one tier of counties further north. The Flood Watch
continues across the region through 11pm.

Several factors in our previous analysis remain true: we have a
very intense (for July) left exit jet region overhead, dew
points are in the low 70s and shear across the region is even
over performing expectations with mesoscale analysis suggesting
upwards of 50 knots available in the 0-6km layer. The locally
lacking ingredient is instability due to widespread rain across
the region this morning. However, a local lack of instability
doesn`t end our severe threat if we can produce instability to
our west and advect storms into the region. This is likely the
way our severe threat is shifting. If storms can form to our
west and move into our incredibly strong dynamic environment
then we still have a very high end severe threat on the table.
If storms do not form west of us and move in then lower level
storms can continue going forward and we may not realize the
full potential of our environment for today. To this point there
is a large area of clearing and Cu popping across IN and
western OH. This activity is already even or south of Pittsburgh
and any activity across our region from this likely focuses our
severe threat Pittsburgh on south, especially along the I-70
corridor.

The amount of shear available in the environment points towards
the possibility of Supercellular or QLCS structures. Each of
these storm modes can bring damaging wind gusts and tornadoes.
Morning rain has acted to locally lower LCLs nodding towards a
possibly improving Tornado threat. Going along with this is
drastically improving structure of our hodographs this afternoon
especially I-70 on south and a noticeable uptick in our SIGTOR
parameter. A Severe Thunderstorm Watch has been issued until 8pm
for all of our OH and WV counties and all of our PA counties
south of a Beaver- Westmoreland line.

Expect lingering showers and non-severe thunderstorms into
early Wednesday before a cold front tracks through the region.

The potential for precipitation remain low through the
remainder of the work week and into the weekend before showers
and storms again look possible on Sunday.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Showers and thunderstorms continue to cross the forecast area
through the afternoon and evening. Much of the terminals east of
ZZV will remain within MVFR and below conditions through the 22Z
timeframe. Heavy downpours will cause vis at some terminals to
drop below 1 mile. Have used mostly TEMPOs during the early part
and some PRB30s to cover later convection.

The main threat of severe storms will likely be over by 23Z. The
overnight tonight will expected to see left over showers and a
few thunderstorms but with flight conditions remaining below IFR
for most terminals due to low cigs.

Towards dawn, expect to see some development of some fog which
could drop vis below 1 mile at times. Winds through the period
will be from the southwest with some gusts up to 30 knots.

Outlook...
There may be some MVFR cigs in the vicinity of DUJ/FKL early
Thursday morning with cool northerly flow. Otherwise, VFR
conditions will prevail under high pressure into Friday.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch until 11 PM EDT this evening for PAZ014-020>022-
     029-031-073>078.
OH...Flood Watch until 11 PM EDT this evening for OHZ040-041-049-
     050-058-059-068-069.
WV...Flood Watch until 11 PM EDT this evening for WVZ001>004-012-
     021-509>514.

&&

$$

DISCUSSION...AK
AVIATION...Shallenberger