762
FXUS61 KPBZ 261914
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
314 PM EDT Wed Jun 26 2024

.SYNOPSIS...
Thunderstorms capable of producing damaging wind and localized
flooding are expected this afternoon and evening ahead of a cold
front. Dry and seasonable weather will return Thursday, with
rising temperature expected Friday.

&&

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

- Flash Flood threat is trending as highest probability focused
  north of Interstate 80.
- A Severe Thunderstorm Watch remains in effect through 10pm EDT
  for northwest PA with damaging wind and hail as the mentioned
  concerns.
- Probability of impact via either wind, hail and flooding
  lowering for locations south of Interstate 80.

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315pm Update:
The area stretching from northeast Ohio to northwest PA
continues to be the focus for flash flood potential as analysis
shows an overlapping maxima of 700-400mb convergence, surface
convergence, rising PWAT values and slow storm motion. Rainfall
rates of 1-2"/hr or higher remain possible, through the axis
likely stays north of I-80 (and potentially even just north of
northern forecast zones). While a Severe Thunderstorm Watch for
northwest PA remains in effect til 10pm, the overall threat
environment for wind and hail seems to be decreasing and
forcing/lift sits north of the region and vort advection from
the southwest continues to spread more stable air (highlighted
by -100 CIN values via MLCAPE mesoanalysis).

Latest hi-res modeling suggests the focus over the first 1-3
hours will be flash flooding along the frontogenetic banding of
heavy rain thunderstorms in northwest PA, which should
gradually progress east through that time. While showers and low
probability thunderstorms remain possible south, the most
likely occurrence is dry weather until the approach of the
surface cold front. A quick surge of warm, moist air at the
surface ahead of the boundary should help destabilize the
environment for thunderstorm development; timing of entering
eastern OH is 5-7pm EDT and reaching western PA between 6-8pm
with storms exiting the entire region generally by 10pm EDT.
There will be a narrow window then for potential damaging
wind/hail and localized flash flooding for areas south of I-80
but the shortened window for instability maximization makes
probability of occurrence low.

Shower and thunderstorm activity is likely to weaken late
tonight as surface instability wanes along with the passage of
the cold front. Much of the severe threat should subside by 10pm
EDT while lingering post-frontal showers and convective
stratiform rain regions exit the higher terrain of WV by early
Thursday morning. Dry air and residual mixing of a NW post-
frontal wind should mitigate morning fog risk, but residual
boundary layer moisture in river valleys (favoring locations SE
of Pittsburgh) could have patchy fog development.

&&

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

- Dry weather returns.
- Temperature rises above normal again Friday.

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

Cool, dry northwest flow will develop Thursday as high pressure
builds in from the northwest. Residual moisture and delay in
subsidence is likely to allow for lingering stratocu Thursday
morning that turns into scattered to occasionally broken
afternoon cumulus. Cold advection and cloud cover will result in
more seasonable afternoon temperature while post-frontal mixing
may support NW wind gusts around 20 mph.

The surface high will shift over New England by Friday as
heights aloft rise ahead of the next upper level shortwave
trough. Positioning of the high will support weak warm, moist
advection amid mostly clear skies to raise area temperature
about 5 degrees above the daily average. Broad ascent may
increase mid to high level clouds and even low probability
showers Friday night as weak perturbations ahead of the main
upper level trough axis.

&&

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

- Shower and thunderstorm chances return Saturday into Sunday
  with the next low pressure system.
- Low probabilities exist for a damaging wind and flooding
  threat with these thunderstorms.

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Broad ascent within warm, moist southwesterly flow ahead of the
main upper level trough axis will support increasing shower and
thunderstorm probabilities starting early Saturday morning.
Arrival of a more notable embedded shortwave and the surface
cold front Saturday afternoon and evening is likely to help
concentrate convective activity (currently favoring NW PA) and
spreading it southeast through Sunday morning.

Variation in storm timing and environment remains large due to
differences in upper trough depth/timing as well as convective
evolution prior to its (and cold fronts) arrival. Latest
analysis suggests a low probability risk for damaging wind
(mean values currently show 30-40kts of 0-6km shear) and
localized flooding (tall-skinny CAPE values around 1500 J/kg
with PWATs approaching daily maxima). Will mention threat in HWO
and monitor evolving forecasts for this period.

Dry weather and seasonable temperature is likely by late Sunday
into Monday as the upper trough axis moves east and high
pressure builds in from the western Great Lakes.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
A broken band of rain showers is currently tracking across the
state of Ohio along a low-level jet. Impacts have only been
noted to visibility at terminal for a brief period.

Restrictions appear promising to start between 20Z and 03Z, as
convection develops along a frontal boundary near Lake Erie and
a shortwave ejects southeast; TEMPO groups continue for all
sites with scattered coverage. Strong to severe wind (40mph to
65mph) gusts could be observed with passing downdrafts and hail
up to the size of quarters could also develop in isolated storms
between 20Z to 00Z. Probability of thunderstorms rapidly
decreases after 04Z (MGW/LBE/DUJ will likely be the last to be
impacted) as the trough ventures east.

MVFR is expected as the thunderstorms end, with a period of
showers.

IFR is likely (LIFR possible) overnight with low level moisture
in place. Restrictions in stratus/fog are possible with all
sites; TEMPOS will be added in the afternoon update.


.Outlook...

VFR is then expected through Friday under high pressure.

Restriction are possible Friday night with a crossing warm
front.

Restrictions are likely Saturday and Saturday night with
showers and thunderstorms ahead of and along a crossing cold
front. VFR returns Sunday under high pressure.

&&

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

&&

$$

SYNOPSIS...Frazier
NEAR TERM...Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...WM/Hefferan