-- Discussion containing changed information from previous version are highlighted. --
459
FXUS61 KPBZ 282308 AAB
AFDPBZ

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
708 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 /UNTIL 6 AM WEDNESDAY MORNING/...
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KEY MESSAGES:

- Scattered showers and thunderstorms diminish this evening
- Additional showers overnight with another approaching
  shortwave
-------------------------------------------------------------------

Scattered showers and thunderstorms will continue to decrease
in coverage through the evening, with loss of diurnal
instability and the passage of a shortwave trough. The latest
mesoanalysis shows a ML CAPE around 250 j/kg, just enough to
support a few thunderstorms. Small hail was likely in some of
the more organized storms, though this potential will continue
to diminish early this evening.

Additional showers are expected to move across the area later
tonight as another shortwave trough approaches. Patchy fog is
possible where rain occurred earlier, though increasing clouds
ahead of the next trough should limit the coverage. Lows are
expected to be near seasonable levels.

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.

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

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
KEY MESSAGES:

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

- Temperatures will continue to remain below average through
  Wednesday night.
-------------------------------------------------------------------

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.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
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.
-------------------------------------------------------------------

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.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
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Activity should continue to wane this evening. 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 morning as the upper trough axis finally rotates
through the region. Another round of showers/storms is possible
Wednesday afternoon, but lightning overage is expected to be
minimal due to limited instability. Light and variable winds
tonight become north-northwest around 5-10 knots on Wednesday.

.Outlook...
High pressure builds into the area Wednesday night through the
end of the week, bringing VFR conditions back to the area
through that time.
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&&

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

&&

$$

SYNOPSIS...Hefferan
NEAR TERM...WM/Hefferan
SHORT TERM...Hefferan
LONG TERM...Hefferan
AVIATION...Cermak/22