165
FXUS61 KPBZ 180756
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
356 AM EDT Sat May 18 2024

.SYNOPSIS...
The risk for showers and a few thunderstorms will continue
through Saturday. Near to above normal temperatures through the
weekend. Dry weather returns Sunday and continues into early
next week with a warmup.

&&

.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:

- Showers and thunderstorms will continue through today.
- Localized urban and small stream flooding issues are possible
  due to slow storm motions and heavy rainfall rates.
  _____________________________________________________________

An upper trough currently centered over the lower Great Lakes
is supporting scattered showers and thunderstorms across the
area this morning. Being almost directly underneath the trough
axis, deep-layer flow is weak and storm motions are therefore
slow, which has led to some minor flooding issues in urban and
low-lying areas and 0.5 to 1.0 in/hr rates are being observed.
This trend will continue through the morning as PWATs hover
around 1.3 inches, though coverage becomes more isolated by this
afternoon as the upper trough shifts to the east, ascent
weakens, and dry air slowly begins to filter into the area.
After an afternoon lull, convective-allowing models are
indicating some redevelopment of thunderstorms will be possible in
the evening, particularly near and over the higher terrain east
and northeast of Pittsburgh. HREF probabilities for 1000 J/kg
CAPE are roughly 50-70% while CAMs are simultaneously showing
potential for upwards of 800 J/kg DCAPE. This could mean better
lightning potential and gusty outflow winds in any storms that
do develop.

Evening thunderstorms dissipate after dark with the loss of
diurnal heating and as an upper ridge builds overhead in the
wake of the departing trough, with dry air continuing to filter
in and clear out any lingering cloud cover. A dry Saturday night
follows with low temperatures running a few degrees above
normal for this time of year.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- Warm and dry weather expected Sunday under building high
  pressure.
_______________________________________________


Upper ridging builds overhead on Sunday, with its axis oriented
from the middle Mississippi Valley northeastward into the Ohio
Valley and lower Great Lakes region. Most of the area will be
warm and dry thanks to subsidence beneath this ridge. The only
exception may be a stray afternoon shower over the ridges of
northeast West Virginia in closer proximity to the southeast
edge of the upper ridge where subsidence will be weaker.
However, even that activity would wane after sunset and give way
to a dry Sunday night. Temperatures continue to run above
seasonal levels throughout this period.


&&

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

- Ridging should result in dry and warmer weather into early
  next week.
- Rain chances return for Wednesday and Thursday, with some
  potential for strong thunderstorms..
  ____________________________________________________________

A dry forecast continues for Monday and into Tuesday as ensembles
largely agree on 500mb ridging and surface high pressure. The rising
heights will lead to increasing warmth; temperatures may climb well
into the 80s by Tuesday, levels last seen early in May.

The ensembles start to diverge a bit on the handling of the next
shortwave trough, which crosses the northern/central Plains and into
the Great Lakes during the Wednesday to Friday period. Cluster
analysis shows some strength and timing differences with this wave,
with GEFS generally more in favor of a slower, weaker wave than many
of the ENS members. These differences point to different scenarios
regarding rainfall amounts and severe weather chances. Still, given
the warmth and potential instability ahead of the system, along with
increased shear, we will certainly need to watch for the chance of
impactful thunderstorms. Both CIPS and CSU machine-learning guidance
continue to point to severe potential on Wednesday and Thursday.
In any case, PoPs in the 50-70 percent range as suggested by the
NBM are justified. Temperatures will remain above normal, but will
likely be muted by Thursday given clouds/rain and a possible cold
frontal passage.

By Friday, scattered showers may remain in a continued troughing
pattern and moisture in low-level northwest flow. Temperatures
may be closer to seasonable levels by this point.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
Save DUJ and FKL which have intermittently observed IFR or VLIFR
this morning and will continue to through daybreak, most ports
are generally sitting VFR to MVFR with temporary drops to IFR
possible in cig and visibility by morning in a saturated airmass
and calm winds.

Scattering and lifting is forecast into the daytime with an
increase in mixing. All ports should return to VFR before fog
and visibility restrictions return overnight again tonight.

.Outlook...
VFR and dry weather become high probabilities Sunday into
Monday under the influence of high pressure.

&&

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

&&

$$

SYNOPSIS...Cermak
NEAR TERM...Cermak
SHORT TERM...Cermak
LONG TERM...CL/Cermak
AVIATION...Milcarek