-- Discussion containing changed information from previous version are highlighted. --
540
FXUS61 KPBZ 090635
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
235 AM EDT Wed Jul 9 2025

.SYNOPSIS...
A meandering boundary remains in our region into the weekend,
with occasional shower and thunderstorms chances. Locally heavy
rainfall remains possible at times, with severe thunderstorm
chances remaining fairly limited.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
KEY MESSAGES:

- Dry weather favored overnight
- Fog development expected again tonight
---------------------------------------------------------------

As the surface boundary settles near to just south of Interstate
68 and the upper shortwaves remains east, the region is favored
to experience dry weather overnight as subsidence aloft takes
hold.

The approach of a western Great Lakes trough will attempt
to increase high to mid level clouds starting around midnight
through Wednesday morning; timing and thickness of these clouds
layers will play a critical role in the development and areal
coverage of fog. Latest model guidance favors river valley
locations and locations south of Pittsburgh where limited dry
intrusion occurred behind the front. Given uncertainty in the
spacial coverage and impacts of incoming higher cloud decks will
preclude any fog hazard products at this time.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY NIGHT/...
KEY MESSAGES:

- Stalled boundary keeps most of the isolated convection south
  of Pittsburgh on Wednesday.
- Better coverage of scattered storms Thursday as boundary lifts
  back north.
- Temperatures just above normal.
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The boundary likely continues to meander south of our region
Wednesday, keeping the deeper moisture/instability to the south and
east. Some isolated diurnal convection remains possible, although
model soundings show some limited capping potential in the middle
levels, keeping a lid on coverage. Any limited severe potential
would exist in portions of northern West Virginia, where better
instability/stronger updraft potential would lie, along with
any potential for localized heavy rainfall, but the overall
threat appears quite low. Temperatures should rise a degree or
two as compared to today, given incipient weak southwest flow.

Convection fades Wednesday night, with Thursday likely dawning
dry. A crossing shortwave trough should begin to push the
boundary north again as a warm front, with a bit more widespread
diurnal convective coverage possible. Skinny CAPE profiles and
low shear suggest that the severe threat remains low, but that
localized high rainfall rates remain possible, especially as
PWAT levels begin to recover.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
KEY MESSAGES:

- Stalled boundary lingers into the weekend at least with
  continued daily rain chances, currently highest Sunday.
- Low rain chances next week as pattern uncertainty increases.
- Continued near to above-normal temperature.
-------------------------------------------------------------------

On Friday, a wave of low pressure along the boundary may push it
back south of Pittsburgh, perhaps towards the Mason-Dixon Line. This
would keep higher diurnal shower/storm chances across our southern
zones. Precipitable water remains elevated near and south of the
boundary, with a reasonable range of 1.3 to 1.6 inches, so locally
heavy rainfall will remain possible.

More organized surface low pressure likely lifts across the western
Great Lakes on Saturday, which would push the boundary back north,
before a potential cold frontal passage Saturday night or Sunday.
There remains ensemble disagreement on how this could play out,
particularly with the timing. For now, Sunday appears to have better
rain chances than Saturday, and given the FROPA uncertainty, the
second half of the weekend also has greater high temperature
uncertainty. NBM 10th to 90th percentile spreads exceed 10 degrees
for most of the region, with possible max values ranging from around
80 to the lower 90s. Severe potential will depend on timing as well,
with ensemble soundings and machine learning advertising at least
low-end potential - forecast deep shear remains on the low side,
limiting organized convection potential. Localized heavy rain
remains possible as well.

Uncertainty them propagates into next week. Elevated 500mb heights
and zonal flow aloft are most likely, keeping temperatures near to
above normal, but differences in disturbances in that flow
require low-end PoPs for both Monday and Tuesday.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
There is still some uncertainty regarding the areal coverage and
degree of intensity for fog formation this morning. Factors favoring
fog include enough boundary layer moisture, very light wind, and a
period of clearer skies fostering strong radiational cooling.
Factors that could limit fog include the influx of mid-high level
clouds overnight ahead of the next shortwave and its timing to
disrupt cooling processes. Cloud cover has remained over eastern
Ohio, allowing for some radiative cooling to occur over western PA
and parts of northern WV. This has resulted in the development of
river valley fog.

The following terminals have a higher likelihood of observing fog:
FKL, DUJ, LBE, and MGW. There is a moderate chance for PIT/AGC
since the river valley fog development has been slower and cloud
cover will reach this area sooner than the eastern terminals.
There is a lower probability for fog at BVI/HLG since these
terminals will soon have cloud cover.

Diurnal heating/mixing will erode any fog/low stratus by 14z, with
VFR expected the rest of the day. Shortwave movement is likely to be
displaced too far north/south to generate precipitation, however,
there is a low probability (30%) for a shower between 18z-00z at ZZV
and MGW. Following sunset, the probability for a rain shower
decreases.

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.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...88
NEAR TERM...88
SHORT TERM...CL
LONG TERM...CL
AVIATION...Frazier/Lupo