276
FXUS61 KPBZ 041948
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
348 PM EDT Thu Jul 4 2024

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

&&

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

- Probabilities increasing for afternoon/evening showers and
  thunderstorms for many locations beyond the previously
  messaged I-70 south region.
- Localized flash flooding with slow moving convection is
  primary concern with a more limited damaging wind threat.

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345pm update...
Showers and isolated thunderstorms (mainly south of the forecast
area) continue to travel east ahead of a noted area of positive
vorticity advection. While this feature is now expected to
continue east and provide lift for convection, weak lapse rates
and diminished instability from cloud cover ahead of the wave
should limit the severe threat. Localized flash flooding remains
a concern, but cells with higher rainfall rates remain very
isolated (or south of region) while forward movement remains
fast enough to mitigate risk (plus dry antecedent surface
conditions). The one area of some concern through 7pm are
portions of Preston/Tucker Counties where a greater
concentration of stronger cells are aiming toward and some
convergence is seen.

The expectation is for a lull behind the passing wave as a
result of subsidence, which could aid hopes for firework
displays this evening. That said, there remains signal for a
secondary shortwave to reignite storms around 00z across
western/central OH and move east; that bears monitoring for 9pm
firework displays across eastern OH.

Rest of the Discussion...

Broad surface high pressure parked over the southeast and upper
ridging across the East Coast keep warm and humid conditions in
the region that will lead to scattered to occasionally numerous
showers and thunderstorms through this evening. The main
concern is localized flash flooding due to near- record PWAT
values, enough column shear, moderate instability (around 1500
J/kg), and weak steering flow. Weak lapse rates and lack of
strong forcing precludes any flood watch issuance as well as
limits probability of a damaging wind threat (in the form of wet
microbursts). These threats will trend down through the evening
and overnight.

Hi-res models suggest increasing coverage of showers and
thunderstorms areawide is expected after 00z/8pm across western
Ohio that will move east ahead of a secondary shortwave.
However, variation in outcomes is high as daytime convective
evolution could alter the model- expected environment tonight.
Severe is not expected, though some there could be enough low-
level modifications to create a very low probability
wind/tornado threat. Flash flooding risks will remain given
unchanged environment.

Have outdoor holiday plans? We recommend checking in on the radar
and forecast every now and then this afternoon in case rain is
moving your way.

&&

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

- More widespread coverage is expected Friday, with damaging
  wind and flash flood threats remaining possible.
- Dry and more seasonable weather returns on Saturday.

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A more organized shortwave and surface low pressure crossing
the Great Lakes will lift the stationary boundary northward as a
warm front and push a late-day cold front through the region.
Breaks in cloud coverage and weak cooling aloft should help
destabilize the otherwise unchanged environment (modest CAPE,
moderate shear, weak lapse rates, high PWAT values). The
expectation is for greater shower and thunderstorm coverage
during the afternoon and evening Friday ahead of each boundary,
with damaging wind and localized flash flooding threats
possible. Improved forcing and instability should be negated by
stronger storm flow to leave the overall flash flood threat
similar to that seen today.

Passage of the surface cold front and upper shortwave will
diminish storm chances Friday night, with dry and seasonable
weather returning on Saturday.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
KEY MESSAGES:

- High probability for dry weather and slightly above average
  temperature the rest of the weekend.
- Unsettled weather returns Tuesday through at least mid-week.

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Confidence remains high in dry weather continuing through the
weekend as surface ridging remains over the Ohio Valley and
upper troughing persists over the Central Plains. Temperatures
should remain near-normal on Sunday, but increasing return flow
and warm advection on Monday ahead of the next low pressure
system will drive daily highs back above-normal. Ensembles
indicate more active weather Tuesday into mid-week as low
pressure crosses and upper troughing sets up across the East.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
Ceilings have generally lifted to VFR/MVFR to start the TAF
period, with additional improvement expected through the
remainder of the afternoon. Scattered showers and thunderstorms
are expected to move across the area through late afternoon and
early evening, and then possibly a second round overnight. Still
a fair amount of uncertainty regarding coverage, prompting VC in
TAFs except in a few scenarios where there is greater confidence
in at least enough coverage to expect impact to a terminal (in
which cases TEMPOs were substituted). Winds remain light and
variable (generally out of the southwest) outside of
thunderstorms. Gusty winds and restrictions can be expected in
and around storms. There is growing confidence in the return of
low cigs Friday morning, especially in areas that see heavy rain
today/tonight.

.Outlook...
Additional rounds of showers and thunderstorms (with occasional
restrictions) are expected episodically through early Sat as a
cold front slowly crosses. VFR should return Sun amid high
pressure.

&&

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

&&

$$

SYNOPSIS...Frazier
NEAR TERM...Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...Cermak/Kramar/Shallenberger