Flash Flood Warning 100, NWS Pittsburgh, PA

Area Forecast Discussion
National Weather Service Pittsburgh PA
259 PM EDT Wed Jul 9 2025

.SYNOPSIS...
A typical warm and moist summer airmass will remain in place
this week and allow scattered afternoon and evening
thunderstorms to develop over the Upper Ohio River Valley each
day. Thunderstorm chances will be a bit higher this weekend as a
weak cold front sags into the area from the Great Lakes.

&&

.NEAR TERM /UNTIL MIDNIGHT TONIGHT/...
KEY MESSAGES:

- Thunderstorms along and south of I-70 corridor
- Severe threat mostly south of forecast area
---------------------------------------------------------------

Surface boundary in West Virginia with weak baroclinic zone to
the north supporting mid to high clouds over much of the area.
Thunderstorms have been confined to area mainly south of
forecast area in West Virginia with stratiform rain region
extending area along and south of I-70. Not much instability to
work with but there are a couple of showers and thunderstorms
north of the MCS in West Virginia and those will produce very
localized heavy rainfall. Despite Corfidi Vectors of 15-20 knots
they have been slow moving.

&&

.SHORT TERM /MIDNIGHT TONIGHT THROUGH SATURDAY NIGHT/...
KEY MESSAGES:

- Weak troughs moving along northern edge of subtropical high
  will support scattered diurnal thunderstorm development
- Low probability of severe and flash flooding at any one point but
  a couple spots could see significant weather each day
- Temperatures a bit above normal with a gradual warming trend
  peaking out on Saturday around 90F
----------------------------------------------------------------

Upper High Centered over Southwestern US as it often does in
summer with subtropical ridge over the southern part of CONUS.
Westerlies continue to stay over the northern states with a
tendency for troughing over the Great Lakes. This results in a
seasonably moist and unstable airmass with daily rounds of
diurnal thunderstorms that will be poorly organized with weak
shear. In fact Corfidi upstream MCS motion vectors become light
and variable for the rest of the weak so expect slow moving
storms that will produce heavy rainfall. Preciptable Water
values around 1.5" will not be excessive but will be high enough
to support locally heavy rain given the slow storm motions.

Mid levels become a lot drier tomorrow so a bit more DCAPE in
profiles and a slightly higher potential for wet microbursts on
Thursday.

Overall not much organization for the thunderstorms and
coveraged will be scattered with very sparse coverage of heavy
rainfall and damaging winds each day. A difficult situation to
message because it is likely that only 1-2 locations each day
are impacted by significant weather. Many spots will be dry each
day and it is difficult more than 6-12 hours in advance to get
your arms around where the chances for impacts will be higher.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
KEY MESSAGES:

- Weak front brings better chance of thunderstorms Sunday
- Not much cooling with temperatures remaining about 5 degrees
  above normal
-------------------------------------------------------------------

Not a lot of change to the pattern and even with weak summer
flow regime a good bit of spread on the timing and intensity of
weak troughs drifting through the Ohio Valley and Great Lakes
areas.

Looks like best shot for a weak front to enhance
thunderstorm chances will be on Sunday. NCAR AI severe
probabilities based on ECMWFE are highest on Sunday and that
seems reasonable. Would also be a higher threat of heavy rain
and flash flooding that day as Precipitable Water values
increase from about 1.5" to the 1.75-2.00" range.

Pattern for Monday thru Wednesday becomes a bit more complex
and uncertain as we could see a series of weak trough/ridge
couplets. Certainly could be a dry day or two in that time range
but not much confidence at this time.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Convective development across northern West Virginia has
overachieved this afternoon so far. Impacts to our terminals
from this should be tied to only MGW as stratiform rain/more
stable nature to the development has shed farther off to the
north. So have included a TEMPO down to IFR in TSRA for MGW
while this batch passes nearby and the rest of the sites (save
perhaps some light rain at LBE) should hold dry with a mid-level
cloud deck and light southwest wind. Following sunset, the
probability for precipitation decreases.

Some fog development is again likely tonight with light to calm
wind and elevated surface moisture. Hi res probability favors
similar development to Tuesday night, especially where rain
falls today, with persistence in a relatively unchanged airmass
bringing elevated chances for 1/4SM vis to 50-60% at MGW, LBE,
HLG, and ZZV. Other sites are less probable to see restrictions
but lesser chances do extend into PIT/AGC.

Additional convection is expected on Thursday after 17-18z and
will take on a scattered nature. Timing will be difficult to pin
down with development potentially off of the lake breeze
initially and then cold pools driving further initiation. Any
showers/storms could bring brief heavy rainfall and gusty wind.
Have included a PROB30 at PIT for now and will continue
evaluating as the timeframe becomes included in the rest of the
TAF sites.

Outlook...
A weakly forced but warm/humid environment is favored through
the end of the week that will allow for intermittent periods of
showers/thunderstorms; confidence is likely to be lower on
timing various rounds of precipitation as well as the resultant
cig/vis impact they could have during the morning hours.

More significant upper level and surface boundary movement appears
to arrive over the weekend that will create a more focused and
better timed period for convection and restriction development.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

SYNOPSIS...Craven
NEAR TERM...Craven
SHORT TERM...Craven
LONG TERM...Craven
AVIATION...MLB

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