639
FXUS61 KPBZ 170629
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
229 AM EDT Thu Jul 17 2025

.SYNOPSIS...
Frontal passage will favor showers and thunderstorms south of
Pittsburgh through Friday while northern locales experience
drier and more seasonable weather. Widespread thunderstorm
chances return Saturday into next week as the active weather
pattern continues.

&&

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

- Frontal passage will support thunderstorms south of Pittsburgh
  and dry/seasonable weather north today
- Higher rainfall rates and increasingly saturated grounds
  creates risk for flash flooding
---------------------------------------------------------------

Brief subsidence between shortwave perturbations will allow for
much of the region to start the day dry with only low
probabilities for an isolated shower.

Weak shortwave movement within quasi-zonal flow aloft will aid
in the eastward movement of a surface low from central MI
towards southeastern Canada today. This will push a surface cold
front SE through the morning that may initially be dry given
weak forcing aloft and CIN in the region. As the boundary
approaches the I-70 corridor shortly after noon, ensemble models
favor an uptick in convective initiation that will lead to waves
of west to east moving thunderstorms through the evening. A
slightly less buoyant/moist environment than Wednesday (SBCAPE
values closer to 1500 J/kg and PWATs closer to 90th percentile)
will still be enough to foster a 1-2"/hr rainfall rates with
localized totals that could exceed 3". Based on increasingly
saturated grounds, high PWATs, and potential for some storm
training as the surface boundary becomes parallel to upper
flow, a Flood Watch for flash flooding was issued for most of
northern WV from 2pm-midnight tonight; this coincides with
WPC`s Slight Risk Excessive Rainfall Outlook.

Hi-res modeling continues to be bullish in dry weather north of
the boundary today, with slight cool/dry advection leading to
more seasonable afternoon temperatures.  The surface boundary
will stall near the I-68 corridor tonight as it becomes
displaced from the upper shortwave, with convective activity
generally dissipating by 06z with the loss of heating/jet
ascent. That said, isolated showers may continue into Friday
morning along the stalled boundary given the warm, moist
environment.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
KEY MESSAGES:

- Diurnally driven convection is expected along and south of the
  stalled boundary, favoring mainly northern WV.
- Areas north of the front are likely to remain dry with
  seasonable temperature.

----------------------------------------------------------------

Quasi-zonal flow aloft with contain very weak perturbations that
will interact with the stalled surface boundary and diurnal
heating to develop scattered thunderstorms mainly over northern
WV Friday. High pressure to the north of the boundary will
support dry, seasonable weather as afternoon high temperature
falls near to slightly below the daily average. For the storm
environment, little air mass change from Thursday means high
PWATs (near 90th percentile) with weak CAPE (less than 1000
J/kg) and weak shear mean localized flash flooding remains
possible. Ensemble signals suggest potential for 1-2"/hr rates
may lay just south of the region, but flood risk will be
monitored given increasingly saturated grounds and generally
favorable training set up (stalled boundary parallel to upper
flow).

Loss of diurnal heating is likely to limit areal coverage of
storms near the I-68 corridor Friday night, but not eliminate
the chances. The approach of additional shortwave energy from
the Upper Mississippi River Valley may act to lift the surface
front (and associated precipitation chances) northward
overnight.

&&

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

- Ensembles trending toward continuing the active weather
  pattern Saturday into next week.
- Flood and severe potential remain highly uncertain and is
  likely largely predicated on prior days outcomes.
-------------------------------------------------------------------

Ensemble models are becoming increasingly bullish on widespread
convection returning to the forecast area Saturday in response
to shortwave movement within developing NW flow traverses the
Great Lakes region. However, there remains a large spread in
wave timing and storm coverage that will be influenced by the
degree of northward lift of the stalled WV boundary as well as
potential SE advancement of some sort of MCS system out of the
western Great Lakes. What can be said is that the warm/moist
airmass featuring 90th percentile and higher PWATs are favored
to be positioned over portions of southeast OH towards Tucker
County (WV) that would suggest an increased risk for flash
flooding. Further NE movement of these PWATs in ensuing model
runs (a possible scenario) would increase that risk further into
western PA. Other hazards like damaging wind can`t be ruled out
either.

The active pattern is favored to continue Sunday into next week
with a series of shortwaves crossing within NW flow as ridging
attempts to build over the MS River Valley. Timing and
variability of conditions remains high but the messaging of
continued flooding and severe threats is likely to continue.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
Areas of MVFR to IFR stratus are expected to continue now
through sunrise with low level moisture in place. VFR returns by
mid to late morning, followed by more showers and thunderstorms
in the afternoon and evening as the surface boundary drifts
south across the region. Focus for convection will likely be
south of the Mason-Dixon, so included a TEMPO at MGW to reflect
the most likely timing for thunder. Farther north, confidence
is lower in impacts at terminals given a more sparse expected
coverage, should any storms form. Maintained PROB30s to reflect
this lower (but non-zero) potential at remaining terminals,
with the exception of BVI/FKL/DUJ where mention of thunder was
kept out due to very low HREF probabilities of storms forming
that far north.

Outlook...
Daily shower and thunderstorm chances are expected to
continue through the weekend, especially in the
afternoons/evenings, as a front becomes quasi-stationary and
drifts across the region. Fog and stratus is also possible each
morning, especially where rain fell the previous day.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...Flood Watch from 2 PM EDT this afternoon through this evening
     for WVZ012-021-509>514.

&&

$$

SYNOPSIS...Frazier
NEAR TERM...Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...Cermak