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612
FXUS61 KPBZ 251516
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1116 AM EDT Sat May 25 2024

.SYNOPSIS...
Dry weather is expected through the morning. The chance for
showers and strong to severe thunderstorms will increase this
afternoon and evening. Sunday is expected to be mostly dry
under high pressure, but thunderstorms will returning Sunday
night into Memorial Day. As we flip the calendars to June,
temperatures fall back to just below normal.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
KEY MESSAGES:

- Dry through most of the morning hours
- Increasing chances for strong to severe storms this
  afternoon/evening with a crossing shortwave
- Damaging wind, hail, and excessive rainfall will be the main
  threats
-------------------------------------------------------------------

A brief period of weak ridging that will keep the area dry through
the morning hours will break down and shunt to the east. A nearly
stalled boundary that has been situated across the area is now
lifting north as a warm front and southerly flow has already
advected low to mid 60s dew points into the area with temperatures
forecast to rise to the low to mid 80s by this afternoon under
continued warm, moist advection.

The 12z PIT sounding doesn`t exhibit much of an impressive wind
field currently, but the upstream ILN sounding and current analysis
shows that low to mid level flow will increase later this afternoon
in tandem with a passing shortwave and just ahead of an approaching
cold front. These will be the initiating mechanisms for today by
early afternoon (most likely after 1-2pm, but possibly as early as
noon) based on latest guidance. There`s also a hint of some
redevelopment along the boundary itself later tonight, but
confidence is low with disagreement amongst the latest CAMs on the
coverage. Hi res ensemble probability indicates that, initially, the
best deep shear will be north and west of Pittsburgh (80% chance of
>30 kt) coincident with better proximity to the passing wave, but
the best instability will be displaced further south (60% chance of
>2000 J/kg) in the area with more residence time in the mostly clear
open warm sector. Nonetheless, the shear increases further south and
the  best overlap of parameters looks to be just north and west of
Pittsburgh by late afternoon with a 50-70% chance of both CAPE >1000
J/kg and deep layer shear >30 kt. Primary threats will be downburst
wind potential and low end severe hail; thetaE minimum (updraft core
height for potential downburst concerns) is around 10kft. Will also
be looking for solid cores to reach above 27kft for severe hail
concerns. Weak low level shear should preclude a tornado threat. SPC
has kept the region in a Marginal Risk (1/5) for severe weather.

Will also have to monitor a low end flood threat as well as we are
in a Marginal Risk (1/5) for excessive rainfall, especially for
areas that got hit hard yesterday (northern WV). Despite PWAT values
topping 1.2", storm motion should help alleviate flooding concerns,
and hi res ensemble probability for >0.5"/hr rates peak on the low
end north of Pittsburgh. Training of storms would likely be see
flash flood threats.

Lastly, areas that receive rain will likely see fog overnight with
ensemble probability of >70% to drop to less than 5 mile visibility.
-- End Changed Discussion --

&&

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

- Dry weather returns through much of Sunday, with
  thunderstorms returning in the evening.
- Strong to severe storms are possible late Sunday night,
  primarily across eastern Ohio.

_____________________________________________________________

Brief ridging builds once again on Sunday, with dry weather
expected through much of the day.

Low pressure will develop across the Plains tonight, lifting
across the Great Lakes by Monday. Moisture will advance across
the region with southwest flow Sunday evening into Monday,
though the latest guidance has slowed the progression of this
system and the eventual onset of convection across the region.
CAMs confine any late afternoon convection to the ridges, with a
pre-frontal line of thunderstorms not nearing our forecast area
until midnight. This timing is not typically favorable for
severe weather in our area, and weakening is expected as these
storms cross into the area. However, a strengthening 30-40kt LLJ
across the area late Sunday night may help maintain several
stronger storms with damaging wind and/or large hail into
eastern Ohio. SPC has highlighted this risk with a Marginal Risk
for that area, keeping the Slight Risk farther west.

Showers and thunderstorms will continue on Monday, with slow cold
frontal passage slowly diminishing rain chances from west to
east into the evening. Daytime surface heating may contribute to
and environment favorable for severe thunderstorm development,
particularly on Monday afternoon. SPC has outlooked the area in
a Marginal Risk.

&&

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

- Near normal to below average temperatures are expected under
  an elongated trough over the Northeast.
____________________________________________________________

Another couple of rainy days look to be in store as a secondary
cold front crosses the region Tuesday and low pressure crossing
to our north on Wednesday. Ensembles then suggest a pattern
change as deep upper troughing develops over the eastern CONUS
with ridging over the Plains. Broad surface high pressure should
finally keep the area dry while temperatures fall back towards
seasonal average.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
High confidence forecast (95%) of VFR through the evening hours
and no precip through 16Z. Confidence falls back into the
40-50% range during the afternoon and evening given uncertainty
with thunderstorm placement.

VFR weather with yield to a developing cumulus field by midday
then as a shortwave trough passes during the afternoon hours,
this will kick off showers and thunderstorms. Brief IFR vis are possible
with the heavier downpours, but it won`t last long /less than
30 minutes/, while CIGS could drop into the MVFR category.

Timing is tricky, so did the best to time in the afternoon
hours, where the highest probs exist and aligns well with the
CAMs.

Any airport that sees a storm this afternoon - early evening
should see at least MVFR fog and some places could even see IFR
fog, but will use later forecasts to fine tune forecasts.

.Outlook...
High pressure and subsidence should promote VFR and dry weather
late Saturday night into Sunday. Fog may develop before dawn
Sunday in rain-soaked locales that experience overnight
clearing.

Thunderstorm probabilities increase overnight Sunday into
Monday as a more robust low pressure system moves through the
Great Lake region. A pattern shift thereafter will introduce
periodic precipitation chances and potential for more prolonged
cig restrictions.

&&

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

&&

$$

SYNOPSIS...Rackley
NEAR TERM...MLB
SHORT TERM...Rackley
LONG TERM...Hefferan/Rackley
AVIATION...Shallenberger/McMullen