785
FXUS61 KPBZ 032148 AAB
AFDPBZ

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
548 PM EDT Wed Jul 3 2024

.SYNOPSIS...
A series of disturbances will create periods of scattered
thunderstorms tonight through Friday, offering low probabilities
for localized flash flooding and gusty wind. Dry weather with
seasonable temperature are expected to return Saturday into
Sunday.

&&

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

- Isolated to scattered showers and thunderstorms expected
  through the overnight period.
- There is a narrow window this evening for a damaging wind
  threat across eastern OH into northwest PA.

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Update...

Showers and thunderstorms continue to advance eastward across
the Upper Ohio Valley region in advance of a shortwave trough.
Most of the storms have weakened as they outrun the instability.
The latest mesoanalysis shows ML CAPE around 1500 j/kg across
northern Ohio to SW Ohio, with lesser amounts to the east. The
greatest downdraft CAPE was analysed across eastern/southeastern
Ohio. One thunderstorm cell near the Coshocton/Muskingum county
line showed signs of organization/bowing, so a warning was
issued as it enters the area of greater DCAPE.

Previous discussion...

A warm, moist environment ahead of the line of showers and
thunderstorms is characterized by rising PWAT values (trending
above 90th percentile), 30kts effective shear, 1000-1500 J/kg
SBCAPE and strong low-level lapse rates. This should support
continued upscale convective growth as the storm axis approaches
eastern OH to northwest PA zones between 4-5pm, generally
forming a broken line of thunderstorms. Despite middling mid-
level lapse rates and weak surface convergence, that environment
could support wet microbursts; the window of hazardous weather
opportunity will be narrow though (~4pm-9pm) as surface based
instability wanes and the upper shortwave lifts NE of the
region.

The loss of daytime heating and upper support will see
convective coverage wane overnight while a surface boundary
slowly shifts southeast into the region. Broad ascent within
southwest flow over a warm, moist environment is expected to
maintain isolated to scattered thunderstorms with limited
impacts.

&&

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

- Scattered to numerous showers and thunderstorms are likely
  Thursday, favoring locations along and south of I-70. These
  storms may pose a localized flash flood threat.
- More widespread coverage is expected Friday, with damaging
  wind and flash flood threats remaining possible.

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Broad west southwest flow will remain in place over the Upper
Ohio River Valley region as the main trough axis sits over the
Central Plains Thursday and Friday. A series of shortwaves will
traverse the region within this flow and tap into the warm,
humid environment to create periodic shower and thunderstorm
chances.

For Thursday, a stationary boundary laying roughly along the
I-70 corridor will serve as a focus for convective development
throughout the day; areas to the south are thus more likely to
see convection while a gradient of decreasing probabilities
exist to the north. Modest instability (around 1000 J/KG), weak
lapse rates, and weak forcing should limit concerns for damaging
wind and localized flash flooding but low probabilities remain
given near record PWAT values, enough column shear, and
potential for some storm training with parallel storm flow and
surface boundary. The afternoon to evening period, where
surface based instability is maximized, is likely when those
threats are maximized before trending down overnight.

For Friday, a more organized shortwave will lift the stationary
boundary northward as a warm front and push through a late day
cold front. Increases in storm motion and lack of parallel
boundary flow should temper flash flood risks, otherwise the
environment should resemble that of Thursday`s but for most of
the forecast region. The afternoon/evening timeframe remains the
most likely period of impact of hazardous weather.

Passage of the surface cold front and upper shortwave will
diminish storm chances Friday night and initiate a period of
drier and more seasonable weather.

&&

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

- High probability for dry weather and slightly above average
  temperature the rest of the weekend.

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Confidence remains high as ensembles show strong agreement of
dry and seasonable weather developing Saturday and Sunday. This
is a result of upper troughing persisting over the Central
Plains and the Upper Ohio River Valley within the dry slot of
southwest flow (plus surface ridging). Expect near to slightly
above average temperature Saturday and Sunday before temperature
returns well above normal Monday (think upper 80s to lower 90s)
as warm, moist advection increases ahead of the next low
pressure system set to cross Tuesday into Wednesday.

&&

.AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
A broken line of showers/storms has developed from near Erie to
west of Cincinnati, which is making slow ewd progress late this
afternoon. These storms are entering a region of lesser buoyancy
across wrn PA, so the expectation is that the nrn segment of the
line will slowly decrease in intensity and erode while the swrn
section of the line may retain some modest intensity.

TAFs were updated to reflect a briefer window for potential tstm
proximity at sites, and to decrease the prolonged nature of
showers overnight tonight at many terminals.

Restrictions settle in Thursday morning around and following
sunrise, with MVFR (potentially IFR) cigs beginning as early as
~10Z, lasting through much of the morning before heating/mixing
allows cloud bases to lift to VFR around the tail end of the
current TAF period.


.Outlook...
Ceiling restrictions gradually improve late Thursday morning
into the afternoon. Additional rounds of showers and
thunderstorms (with occasional restrictions) are then expected
Thursday afternoon through early Saturday as the front slowly
crosses. VFR should return Sunday under high pressure.

&&

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

&&

$$

SYNOPSIS...Frazier
NEAR TERM...WM/Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...Cermak/Kramar/Rackley