-- Discussion containing changed information from previous version are highlighted. --
743
FXUS61 KPBZ 181746
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
146 PM 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 /UNTIL 6 PM THIS EVENING/...
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 is currently centered over the lower
Great Lakes. The trough supported scattered showers and
thunderstorms across the area this morning, with especially
heavy rain in Allegheny County. Rain rates have come down over
the past couple of hours, with an area of lighter showers
currently east of Pittsburgh. Isolated coverage at best is
expected into early 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. Slow storm motion could also lead to
isolated instances of heavy rainfall once again.

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 /6 PM THIS EVENING 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 /18Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --
A scattered to broken VFR convective type cloud deck has taken
over this afternoon as convective temperatures are achieved.
Very weak boundary layer flow will generally keep wind variable
at 5 knots or less through this evening, perhaps favoring a
northerly direction. Widely scattered showers and thunderstorms
are expected to develop this afternoon after 19z (20-40%
chance... highest to the east), but with no real defined surface
forcing mechanism aside from orographic influence, confidence
is low in impacts to any one terminal at any given time. As
stated, hi res ensemble favors development primarily east of PIT
and potentially affecting at LBE/DUJ with brief restrictions in
TSRA.

Showers and storms will dissipate after 00z and give way to more
widespread restrictions again possible overnight tonight with
lingering low level moisture in place and wind going mostly
calm. Probability for MVFR to IFR VIS returns to 40-70% and with
less cloud coverage and no rain expected, confidence is a bit
higher tonight than Friday night for fog development. FKL/DUJ
have a low to moderate probability of LIFR VIS.

Ridging builds on Sunday and VFR returns with high confidence
after mixing dissipates the fog and erodes any lingering
scattered cloud deck in the morning. Wind will again be light
during the day with a weak pressure gradient in place.

.Outlook...
VFR and dry weather remain high probabilities into Monday and
Tuesday under the influence of high pressure. Precipitation
chances and associated restrictions return Wednesday.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...Cermak/22/CL
NEAR TERM...Cermak/22/CL
SHORT TERM...Cermak/CL
LONG TERM...Cermak/CL
AVIATION...MLB