393
FXUS61 KPBZ 041707
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
107 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 /THROUGH TONIGHT/...
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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1pm update...
Latest analysis shows weak convergence along a rough W-E line
near I-80 that has led to scattered showers and low
probabilities thunderstorms. Farther out west, a notable area of
vort advection is maintaining a shield of mostly moderate rain
showers and developing new convection along its southern flank.
Based on mesoanalysis showing ~1500 J/kg SBCAPE with breaks in
area cloud cover likely offering further destabilization, the
expectation is for persistence of ongoing storms with an uptick
in coverage favoring the I-80 corridor PLUS south of I-70
through 4pm this afternoon. Weak model handling of current
situation suggests a continuation of updating priors is required
to best project future anticipation.

Overall threats are similar to prior discussions, as high PWAT
and weak steering flow makes localized flash flooding the
primary concern while low probabilities for damaging wind
remain.


Previous 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 through this evening 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 later tonight ahead of the
approaching trough. However, variation in outcomes is high as
daytime convective evolution could alter the model-expected
environment tonight.

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 /FRIDAY 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 WEDNESDAY/...
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.

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

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 /18Z THURSDAY THROUGH TUESDAY/...
A mix of cigs kicks off the TAF period as terminals range from
IFR to VFR, based primarily on where the heaviest rain fell in
the past 12-24 hours. Conditions gradually improve to VFR
areawide by late morning or early afternoon. A few isolated
showers are ongoing in the PIT/AGC/LBE area and VCSH has been
included to start the TAF period to reflect this activity.
Elsewhere, scattered shower and thunderstorm activity ramps up
this afternoon and evening, though uncertainty remains rather
high regarding the coverage and intensity of convection and
therefore mostly VCSH/VCTS has been maintained in TAFs. Expect
an overall weakening trend in convection after 00Z with
instability waning overnight. A weak front stalled across the
area will continue to result in generally light and variable
winds throughout the period, with the exception of gusts in and
around thunderstorms. Restrictions likely return early Friday
morning, especially in areas that see rainfall 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