-- Discussion containing changed information from previous version are highlighted. --
781
FXUS61 KPBZ 110602
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
202 AM EDT Fri Jul 11 2025

.SYNOPSIS...
Scattered afternoon and evening thunderstorms expected daily
through the weekend with the highest chance on Sunday as a weak
cold front crosses the area. The first half of next week may be
drier ahead of another late week disturbance. Temperatures will
remain a few degrees above normal.

&&

.NEAR TERM /THROUGH TODAY/...
KEY MESSAGES:

- The threat of thunderstorms have come to end this evening
- Another night of fog potential tonight
---------------------------------------------------------------

Evening Update...The daytime heating has begun to wane and the
cap is setting in for the evening. This should cut off any
further thunderstorm development through the rest of the
evening and overnight. Thus have removed pops after 01Z. A stray
shower is still possible but the overall threat is largely
over. Some areas of fog will be possible tonight.

Previous discussion...Stubborn low stratus will gradually erode
this morning but is taking its time doing so. Where it has
cleared, temperatures have risen rather quickly with efficient
solar insolation. This will set the stage for scattered
afternoon and evening showers and storms.

Initiation should be off of the lake breeze as well as a
differential heating boundary in east-central Ohio on the clear side
of the morning stratus after 17z. The environment today will be
supportive of heavy rain and possibly damaging wind within any of
the strongest storms. CAMs suggest up to 2000 J/kg MLCAPE with weak
effective shear around 15-20 knots. Corfidi upshear vectors values
are low, but a bit more than we`ve had in the past couple days, also
around 15-20 knots which should allow for the stronger storms to be
a bit more transient. Still, with our 12z sounding of a 1.34 PWAT,
we`ll still have some heavy rain producers and a localized flash
flooding threat if any storms sit or train long enough over the same
area. The damaging wind threat will be from downbursts, though
there`s some question as to how vigorous the updrafts will be able
to get. Our sounding and most of the 12z CAMs depict 1) a warm layer
around 700 mb that may act as a cap, at least until repeated
updrafts could erode it, and 2) a lot of dry air above 600 mb,
potentially enough to inhibit development above it. This means that
updrafts could look strong in the lower levels, up to around
freezing level to -10C, but with not much structure above there at
least until wet-bulbing would occur and could grow the CAPE profile
a bit. So the downburst threat will be there contingent on higher
updraft heights of which we`d be looking solid for 50 dbz returns to
reach around 19-20kft.

Timing of storms at any given location will be tough to pin down as
cold pool interaction will drive downstream development, but the
best window for our area will be after 12pm through sunset, starting
to the north and west before meandering farther south.

Drier conditions take hold tonight but expect that another night of
fog is likely given a stagnant airmass and persistence. It will be
at its most dense in areas that seen rain today, but plenty of near-
surface moisture, calm wind, and scattering clouds will support it
across a lot of the area and it could be dense in spots again. Lows
will be mild in the mid to upper 60s.

&&

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

- Scattered afternoon and evening showers and storms Friday and
  Saturday
- Heavy rain and damaging wind threat with stronger storms
----------------------------------------------------------------

Diurnally driven convection will continue to be the story on Friday
and Saturday with continued weak flow aloft, though subtle mid-level
height rises will occur. Ensemble mean PWAT values remain similar to
Thursday around 1.3-1.5" with weak flow and a 50-80% chance of
SBCAPE values >1500 J/kg each day. DCAPE values sit around 800-1100
across the 12z CAMs again supportive of a very localized heavy
rain and downburst threat. Pegging down exact timing and
location of development again is a fool`s errand, especially
with the influence of remnant outflow boundaries from previous
days. There are suggestions that it may be more terrain driven
with higher coverage in the ridges and to the east, but would
have to believe that remnant outflow and the lake breeze could
again play a role.

Outside of convection, temperatures will climb a bit into the
upper 80s on Friday and increased probability as high as 90% in
the urban areas and valleys (50-70% elsewhere) to reach 90F
Saturday.

&&

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

- Wetter on Sunday with a crossing boundary
- Potentially drier first half of next week ahead of another
  low pressure system passage by mid to late week
- Temperatures remain above average
-------------------------------------------------------------------

Sunday looks to be the wettest day of the weekend as low pressure
tracking across the Great Lakes drags a surface cold front through
the area. The best shortwave support will track north of Lake Erie,
but there will be a plenty warm and moist airmass in place for the
boundary to work upon. Confidence is high that it passes on Sunday,
but the deterministic guidance still suggests different timing which
would impact any severe or flooding threat. Machine learning
suggests there could be a severe threat, contingent on an afternoon
to evening timing, but organized severe weather seems less likely
given still weak shear as the strongest flow remains to our north.
Will continue monitoring as the CAMs come into play.

A more potent mid-level wave swings through on Monday in better
amplified flow and could provide more afternoon and evening showers
and storms, though ensembles deviate a bit here with the post-
frontal environment. Some suggest a surface high quickly building in
the wake of the front while others don`t bring the high in quite
that quickly and allow for another unsettled day on Monday. NBM
still supports 30-60% PoPs, highest to the south and east, but it`s
possible that that could trend drier if the more progressive
solutions prove correct. Not much of an airmass change is likely
behind the front, so still expecting above average highs on Monday.

Tuesday and Wednesday show indications of being drier across the
board as aforementioned high pressure does settle in and upper
ridging builds from the southwest. This will allow temperatures
to climb with warm advection in southwesterly flow bumping 90F
probability back up to 50-70% on Tuesday and 60-80% on
Wednesday, again highest in the urban areas. Ensembles track yet
another low pressure system out of the Great Lakes Thursday
into Friday which will likely bring another cold front through
and return rain chances. Still seeing a good bit of disagreement
on timing and amplification of the responsible mid-level
trough, so confidence is low this far out, but it`s less likely
that we keep the dry weather around through the end of the week.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
A moist boundary layer combined with calm wind and partly clear
overnight skies will foster strong radiational cooling that
results in fog between 06z-12z. An analysis of fog/stratus last
night showed that the UPS fog method (focusing on daytime
minimum dew point and the time overnight temperatures reach that
value) performed well. The biggest variable change between last
night and tonight is the lack of rain to reinforce surface
moisture and diurnal mixing that introduced some drier air to
the surface. Thus, following a similar methodology, fog
probabilities have trended lower (but still present) at most
terminals through early morning.

Insolation will burn off any developed IFR/LIFR fog/stratus by
mid morning and aid in isolated thunderstorm development after
18z Friday. Hi-res modeling is bearish on potential, favoring
locations in western PA and northern WV, so kept prob30 wording
for those terminals.

Outlook...
A weakly forced but warm/humid environment is favored through
Saturday 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/vsby impacts they could have during the morning hours.

More significant upper-level and surface boundary movement
appears to arrive Sunday, which will create a better focused
period for convection and restriction development.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...MLB
NEAR TERM...MLB/Shallenberger
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Frazier/Cermak