PBZ issues Area Forecast Discussion (AFD) at Jul 4, 9:09 AM EDT500
FXUS61 KPBZ 041309
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
909 AM 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:
- Scattered showers and thunderstorms are possible today,
favoring locations along and south of I-70. These storms may
pose a localized flash flooding and strong wind threat.
- Should not be a washout for your Independence Day plans, but
remain weather-aware.
-------------------------------------------------------------------
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 isolated/scattered showers and
thunderstorms favoring the afternoon and evening hours. The
focus for activity will mostly be along and south of a
stationary boundary lying along the I-70 corridor. For those of
us north of I-70, this will mean mainly dry conditions save for
a few stray showers and thunderstorms today. Those south of I-70
will see increasing coverage this afternoon and evening, but
should still remain scattered, and shouldn't be a full
afternoon washout.
South of I-70, 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. Any flooding or severe wind threat will be
maximized in the afternoon/evening period when surface-based
instability will be maximized. These threats will trend down
through the evening and overnight.
With persistent cloud cover through much of the day, high
temperatures will end up nearer to seasonal norms and about 5
degrees cooler than what we saw Wednesday.
Increasing coverage of showers and thunderstorms areawide is
expected later tonight ahead of the approaching trough, but
this should be after [most] firework shows are over (we all have
that one neighbor...).
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.
-------------------------------------------------------------------
By Friday, a more organized shortwave and surface low pressure
crossing the Great Lakes will lift the stationary boundary
northward as a warm front, eventually pushing a late-day cold
front through the region. Increases in storm motion and lack of
parallel boundary flow should temper flash flooding risks.
However, the environment will remain similar to today, but with
convective coverage expanding to most of the forecast region.
The afternoon/evening timeframe remains the most likely period
of impact of hazardous weather (primarily damaging wind). Cloud
cover and limited insolation/surface destabilization is likely
to again be the limiting factor for severe weather, but guidance
indicates a more favorable thermodynamic profile for severe
weather Friday versus today. More robust breakup of late
morning/early afternoon cloud cover than is currently forecast is
likely to mean more robust convective development in the
afternoon.
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 /13Z THURSDAY THROUGH MONDAY/...
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...Rackley/Frazier
SHORT TERM...Rackley
LONG TERM...Rackley/Frazier
AVIATION...Cermak/Kramar/Shallenberger
Source:
PBZ issues Area Forecast Discussion (AFD) at Jul 4, 9:09 AM EDT---------------
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