-- Discussion containing changed information from previous version are highlighted. --
251
FXUS61 KPBZ 281828
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
228 PM EDT Tue May 28 2024

.SYNOPSIS...
Two passing shortwaves over the Great Lakes will keep rain and
thunderstorm chances elevated today and tomorrow. Cooler than
average temperatures are expected through Friday.

&&

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

- Shower and thunderstorms chances increase after 12pm with a
  passing shortwave from the northwest. A few storms may have
  small hail (pea sized).
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1:30pm: Sporadic shower activity has increased north and west
of Pittsburgh over the last hour. Lightning chances are
currently low given updrafts being confided near or just below
the freezing level. However, thunder chances will increase due
to the peak surface heating time frame and cold advection
aloft.

Previous Discussion:

A deep upper-level trough is currently tracking trough the Great
Lakes and Midwest region. Embedded with this large scale
pattern is numerous shortwaves that will impact the Ohio River
Valley. The first shortwave, currently tracking trough northwest
Ohio, will reach western Pennsylvania in the next 2 to 3 hours.
With diurnal heating from breaks in the clouds and cooling
aloft, elevated instability will build across the region;
Hi-Res guidance suggests 300J/kg to 700J/kg of MUCAPE. Therefore,
thunderstorms and showers will initiate easily with the noted
low to mid-lvl ascent associated with the shortwave. A few
storms may have small hail given a lower freezing level (below
9kft) and drier conditions in the mid-levels. Updrafts that can
climb above 11kft have the best chance at producing hail.

Besides convection, cooler than average temperatures are
expected under northwest flow, an increase in cloud coverage,
and lingering convection. Afternoon high temperatures will trend
5 degrees below average.

Rain intensity will decrease after 10pm with the loss of surface
heating, but remnant showers may linger passed midnight with
the exiting shortwave and a new disturbance entering central
Ohio.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --
KEY MESSAGES:

- Rain and thunderstorms chances continue into Wednesday with a
  new disturbance.

- Temperatures will continue to remain below average through
  Wednesday night.
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An ejecting shortwave trough over the Midwest will initiate
showers and thunderstorms Wednesday across the region.
Instability and effective shear will be considered weak, MUCAPE
400J/kg to 800J/kg and less than 25kts. However, training storms
could create a swath of heavy rain (between 0.45 to 0.65
inches) across the region during the late morning to late
afternoon.

Precipitation chances will quickly diminish between 9pm and
11pm Wednesday night with the loss of surface heating and the
shortwave exiting east.

Below average temperatures will continue Wednesday afternoon
into Wednesday night under cool, northwest flow.
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&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
KEY MESSAGES:

- Dry weather and cooler temperatures are expected Thursday into
  Friday under high pressure.
- Rain chances may increase Sunday into Monday with a shift in
  the synoptic pattern. However, confidence is still considered
  low on timing and strength of the overall disturbance.
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Surface high pressure builds into the area on Thursday. Dry,
cool conditions will continue into early Friday.

A ridge will advance into the Ohio River Valley late Friday into
Saturday and return warm conditions.

Thereafter, spread in the models increases regarding how quickly the
upper ridge moves off/breaks down and how quickly deeper moisture
returns. NBM suggests low PoPs for Sunday and Monday (30 to 40
percent) with temperature expectations of near to slightly
above seasonal levels. Stout ridging in place as this next
disturbance arrives may lead to a difficult forecast given the
subsidence and drier air in place to start the new week.
-- End Changed Discussion --

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
A broken cu field with VFR cigs (save for FKL/DUJ where MVFR
continues) has formed across the area as well as scattered showers,
which so far have been mostly confined to areas along and north of
the I-80 corridor. Expect this shower activity to continue becoming
more numerous across the rest of the area as we head into the
afternoon hours, with a few thunderstorms also possibly mixing in.
This activity wanes some after 02Z, though a stray lingering shower
overnight cannot be ruled out. Widespread cig restrictions settle in
early Wednesday morning with lingering low-level moisture and cold
advection dominating. Hi-res ensemble guidance is suggesting high
probabilities (70%+) for widespread MVFR/IFR and even medium
probabilities (40-60%) of at least some instances of LIFR occurring
at all area terminals. Another round of scattered to numerous
showers also develops Wednesday as the upper trough axis finally
rotates through the region. Minimal lightning is expected, even
during the afternoon, due to limited instability. Light and variable
winds tonight become north-northwest around 5-10 knots on Wednesday.


.Outlook...
Pivoting of the upper trough through the region Wednesday will
generate widespread showers and an off chance at a rumble of
thunder, along with widespread cig restrictions. High pressure
builds into the area Wednesday night through the end of the week,
bringing VFR conditions back to the area through that time.

&&

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

&&

$$

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