264
FXUS61 KPBZ 220802
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
402 AM EDT Mon Jul 22 2024

.SYNOPSIS...
Shower and thunderstorm chances increase today with an
approaching disturbance from the south. Temperatures remain
seasonable throughout the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
KEY MESSAGES:

- Probability of showers increases after dawn with an advancing
  weak disturbance.
- Probability of thunderstorms increases after 1pm; the best
  potential to observe a storm will be south and east of
  Pittsburgh, PA.

______________________________________________________________


A weak shortwave, embedded within a large scale trough over the
Great Lakes, will advance north early this morning and return
precipitation chances to the region after 6am. At the moment,
mid-level dry air is lingering across the region (depicting in
GOES-16 vertical temperature profiles) and keeping low-lvl
clouds from forming. However, with a blanket of upper-level
clouds noted on satellite overnight low temperatures are hardly
falling; it is still in the low-70s at PIT at 2am.

Probability of thunderstorms increases significantly (above 50%)
within the Hi-Res model guidance after 1pm southeast of
Pittsburgh, PA as surface instability ranges between 700J/kg to
1200J/kg and warm front advances. There is a noted maxima in
low- level convergence over Tucker, Preston, Fayette, and
Westmoreland county that remains stationary between 2pm to 8pm
due to southeast flow over the Laurel Highlands and northwest
winds prevailing over Pittsburgh at 850mb.

Along with thunderstorms, higher rainfall rates will be
generally focus along the ridges as PWAT values range above
average (1.6-1.8 inches noted in Hi-Res model soundings).
Probability of rainfall totals (0.5 inches or higher for the
ridges) ranges between 60% to 80% through the late evening.
Isolated areas may receive over an inch of rain with training of
robust storms.

With effective shear weak (below 30kts) and DCAPE values likely
below 600J/kg, strong to severe wind gust potential will be
low. Small hail may form for updrafts that produce strong
reflectivity above 20kft.

Probability of thunderstorm decreases after 10pm with the loss
of surface heating and as the shortwave exits northeast.

With clouds and precipitation chances throughout the day,
afternoon high temperatures will likely trend near or below
average.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/...
KEY MESSAGES:

- Fog is expected to impact the region early Tuesday morning.
- Precipitation chances will remain low Tuesday morning and
  early afternoon with ridging.
- A new weak shortwave may return isolated showers and storms
  Tuesday evening.

_________________________________________________________________

As precipitation chances decrease early Tuesday morning, the
probability of low visibility due to fog increases to 60% for
portions of the region between 2am and 7am. A special weather
statement (SPS) and/or Dense Fog Advisory may be needed if a
prolong period of dense fog (1/2NM -1/4NM develops. At the
moment, Hi-Res model guidance is spatially favoring fog
developing east of Pittsburgh (mostly associated with the
potential of heavy rainfall Monday afternoon/evening). However,
probabilities could increase further west if convection
ventures near the border of eastern Ohio.

Fog may linger as late as 9am or 10am due to cloud coverage
delaying diurnal mixing.

Precipitation chances will likely remain low through Tuesday
evening under ridging.

Probability of isolated showers and thunderstorms increases
between 4pm to 8pm with a new weak shortwave advancing from the
southwest.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
KEY MESSAGES:

- Shower and thunderstorm chances continue through Thursday.
- Near-normal to slightly above average temperatures are
  expected through Friday.
- Above average temperatures and dry conditions are expected
  over the weekend.
  ________________________________________________________________

The Great Lakes trough and ridge axis off the Atlantic Coast will
continue to push moisture from the southwest into the Upper
Ohio Valley Wednesday and Thursday, keeping rain and
thunderstorm chances in the forecast. A cold front is expected
to cross the region early Thursday morning. Probability of
strong to severe storms during this period is low (less than
10%).

A shift in the synoptic pattern, a building ridge over the
Midwest and western Great Lakes, will return dry weather and
above average temperatures into the weekend. Probability of
>=90F afternoon high temperatures range between 25% to 50%
across the region on Sunday.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
VFR is expected through at least this morning ahead of an
approaching shortwave trough. Mid level cigs should gradually
lower through the afternoon as the shortwave approaches, and
scattered showers and thunderstorms develop and move across the
region.

Instability is expected to be minimal for much of the area.
Included -shra or VCSH for most ports, with a VCTS at PIT where
instability is marginal for an embedded thunderstorm. Guidance
indicates slightly more favorable instability to the east, with
MU CAPE 500-1000 j/kg. Included a tempo group for thunderstorms
from DUJ-LBE-MGW this afternoon, with these sites more likely
to see a thunderstorm. Visibility restrictions are possible in
any showers, though confidence was too low to include this
outside of any tempo thunderstorms. The shortwave is expected to
exit the region this evening, with mainly mid level clouds
continuing. Areas near DUJ could see MVFR cigs/vsbys developing
toward midnight, especially if rain occurs during the day.

.Outlook...
Restrictions in stratus/fog are possible Tuesday morning,
especially where rain occurs Monday. Scattered showers and
thunderstorms and restrictions, especially during the afternoon
and evening hours, are expected through Wednesday, as shortwaves
embedded in southwest flow cross the region. Showers and
thunderstorms are likely on Thursday with the passage of a cold
front. VFR returns Friday under high pressure.

&&

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

&&

$$

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