286
FXUS61 KPBZ 151136
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
736 AM EDT Wed May 15 2024

.SYNOPSIS...
Scattered showers and a few thunderstorms are expected as an
upper trough crosses the region, with the best rain chances
lying north and west of Pittsburgh. Showers and storms will be
possible again Friday and Saturday after a dry Thursday.

&&

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

- Shower/thunderstorm chances greatest NW of Pittsburgh.
- More scattered showers to the south and east of the city.
- Near-normal temperatures.
  ______________________________________________________________


The morning update mainly focused on reconfiguring PoP fields to
place better probabilities to the north and west of Pittsburgh.
A slow-moving boundary lies close to this region. Weak
east/southeast flow into this boundary, along with modest
instability eventually reaching the 600-800 J/kg range, will
allow for a bit more widespread shower/thunderstorm activity
than areas to the south and east. Overall forcing is weak with
the upper trough centered over the Middle Ohio Valley, and shear
profiles/weak CAPE do not suggest a severe threat. However, that
weak flow will contribute to slow storm motions, and with
precipitable water on the high end of the seasonal climatology,
locally heavy rainfall totals are possible in the western CWA.
An isolated high water issue or two cannot be ruled out, and
WPC`s marginal excessive rainfall outlook is well-placed.
Temperatures today will end up close to seasonal norms.

&&

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

- Ridging provides drier weather tonight through Thursday.
- Near to above normal temperature expected.
  ______________________________________________________________

Precipitation coverage should wane this evening as the trough
axis shifts east of the region and heights rise aloft. With
ridging the dominant feature, warmer temperatures and dry
conditions are then forecast through Thursday night, although
some showers may begin to show up in the western CWA prior to
12Z Friday ahead of the next shortwave.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
KEY MESSAGES:

- Forecast uncertainty increases during the extended period.
- Another trough is likely to provide unsettled weather at least
  for Friday and Saturday, although rain amounts are iffy given
  the uncertainty.
- Temperatures near or above normal are expected.
  ______________________________________________________________

Uncertainty creeps upward in the extended period.  The mid-level
ridge will be departing the Appalachians Friday morning, with
moisture increasing once again ahead of the next trough, which
ensembles have crossing the Mississippi River Friday evening and
reaching the Upper Ohio Valley by Saturday.

Thereafter, speed and timing differences arise in the models with
the handling of this trough. GEFS/GEPS members are favoring a
quicker departure and a weaker trough, while ENS favors the opposite
outcomes. Differences then continue to get larger from there, with
cluster analysis indicating anything from strong ridging to the
presence of a closed upper low is on the table by early next week.

A good example is looking at NBM 10th/90th 72hr QPF percentiles
for the weekend....ranging from 0.04" to 1.38" for the
Pittsburgh metro area.

Will continue to roll with the NBM suggestions for the extended
period and wait for increased model clarity. This would suggest
a return of unsettled, but likely not overly impactful weather
Friday and Saturday, with lower rain chances during the early
part of next week. Near to slightly above normal temperatures
are currently forecast, but again, there is a sizable range of
outcomes here.

&&

.AVIATION /11Z WEDNESDAY THROUGH SUNDAY/...
Low pressure near the OH/KY border (with an inverted surface
trough extending north) will continue to drift eastward today,
eventually weakening into a trough as a new surface low develops
off the Mid Atlantic coast. MVFR should become widespread later this
morning as cigs lower with increasing low level moisture around
the low. The exception will be FKL and DUJ, where moist
easterly flow should maintain IFR cigs.

Scattered showers and MVFR cigs (IFR at FKL/DUJ) will continue
today as the low moves eastward. Some improvement to low VFR is
expected through the afternoon with surface heating and mixing.
The greatest amount of destabilization is expected near the
inverted surface trough, which is expected to be near DUJ-FKL-
ZZV this afternoon. A band of MU CAPE in the 500 to 750 j/kg
range is depicted on the latest HREF output in this vicinity.
Maintained a prob30 for thunderstorms for those ports affected,
with showers mentioned just to the east of this boundary where
less instability is progged. A thunderstorm is possible at PIT,
though confidence was too low for TAF inclusion.

Cigs should lower to MVFR again this evening as the trough
dissipates across the Upper Ohio Valley region, but low level
moisture remains.

.Outlook...
VFR should return Thursday under a ridge of high pressure.
Periodic restrictions and showers are expected Friday through
Sunday with another slow moving low pressure system.

&&

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

&&

$$

SYNOPSIS...88
NEAR TERM...CL
SHORT TERM...88
LONG TERM...CL/88
AVIATION...WM/CL