421
FXUS61 KPBZ 100058 AAA
AFDPBZ

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
858 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:
- Potential for occasional fog overnight
---------------------------------------------------------------

A stabilized airmass is noted near and north of a stalled sfc
boundary across ern OH to swrn PA. The airmass is currently
characterized by cool temps in the low-mid 70s F and dews
approaching 70F. Although a good deal of mid-level cloud cover
remains, radiational cooling amid decoupled sfc wind will
promote at least patchy fog development overnight. Otherwise, no
notable weather impacts are evident, with lingering storms
remaining well to the south of the Upper Ohio Valley.

&&

.SHORT TERM /THURSDAY 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 /00Z THURSDAY THROUGH MONDAY/...
Fog development is likely tonight with light-to-calm wind and
a near-saturated low-level airmass. Hi-res model ensemble shows
highest probability (60%+) of IFR/below vsby in the area that
experienced the most/most-prolonged rain today: primarily along
and south of an axis from near PHD to BVI to LBE. North of this
axis, localized fog is possible (30-40% chance). Given that
probability of sub-6SM vsby and sub-2SM vsby are virtually
identical at all sites, the implication is that fog occurrence
is less certain, but if it occurs, it is likely to be IFR or
below. If not for the lingering clouds slowing down cooling,
dense fog would be more confident. However, the lingering clouds
are likely to limit dense fog formation on a widespread basis,
and any such observations at terminals ought to be localized.
For now, have taken terminals to MVFR or IFR (2-5SM), but it
remains possible that cigs or vsby could reach categories lower
than that.

Any fog is likely to dissipate quickly Thu morning with a broad
return to VFR conditions. Additional storms are expected after
18z and will present as more scattered in coverage. Timing will
be difficult to pin down with development potentially off of
Lake Erie`s lake breeze initially, with subsequent initiation
driven by storm outflow. Any showers/storms could bring brief
heavy rainfall and gusty wind. PROB30 was included at all sites
for now, pending refined mesoanalysis Thu morning, which could
help identify targeted areas and timing.

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/vsby impacts they could have during the morning hours.

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

&&

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

&&

$$

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