-- Discussion containing changed information from previous version are highlighted. --
706
FXUS61 KPBZ 250003
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
803 PM EDT Tue Sep 24 2024

.SYNOPSIS...
A passing low pressure system may bring showers and a few strong
to severe storms this evening. A few areas may also experience
heavy rainfall that could prompt flash flooding.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
KEY MESSAGES:

- Strong to severe storms still possible, mainly across OH and
  nrn WV this evening
- Scattered showers overnight

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Update...
The latest mesoanalysis shows the highest ML CAPE (500-1000
j/kg) across western and northern Ohio. Earlier convection has
eroded the available CAP across northern WV. Strong shear
remains in place across the region, with 35-45kt effective bulk
shear on the latest mesoanalysis. Will monitor the storms across
OH, through current indications are the strongest should stay
west of our area. More storms across eastern Kentucky will also
approach OH and WV later this evening, though these should
decrease in strength as they approach with slowly waning
instability. There is still a potential for severe weather this
evening, mainly across OH and nrn WV, though this potential
appears to be lowering.

Previous discussion...
A surface warm front is currently situated near the I-70 region
over eastern Ohio. Additional convection will likely develop
along and/or behind this noted boundary and track northeast this
afternoon as the low-level jet enhances over southeast Ohio.

Shear is plentiful, effective shear in the next few hours will
increase from 25kts to 40kts southwest of Pittsburgh. Also, with
low-lvl wind shear (below 3km) directed from the southeast, the
hodograph depicts helicity values between 50m2/s2 to 100m/s2
that could prompt rotating updraft and create a tornado risk
in a few storms. The Storm Prediction Center (SPC) highlighted
the potential of tornadoes south of I-70 with a 2% circle that
extends into ILN/RLX`s region. However, with heavy cloud
coverage and disorganized convection from early this morning,
storms may struggle to develop due to weak instability.

Along with a damaging winds/tornado threat, there is also a
flash flooding threat today. Precipitable water values are well
above average (1.6" to 1.8") and there is a noted warm cloud
layer (about 10kft). Training storms over urban areas will
likely need to be closely monitored throughout the evening.

&&

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

- Rain chances continue through mid-week.

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Showers and weak thunderstorms will likely be ongoing early
Wednesday morning as a trough continues to move across the Ohio
River Valley. The potential of strong storms will be considered
low given weak instability and the absence of a lifting
mechanism.

By 8am Wednesday, the cold front will likely be positioned in
western Ohio and stall due to the mean flow orientated parallel
to the boundary. Showers and storms may redevelop in eastern
Ohio along the stalled frontal boundary and along any
moisture/temperature gradient boundaries that develop after
12pm.

Shower and storm potential is expected to decrease after 10pm
with the loss of surface heating.

Above average temperatures are expected through this time period
under deep southerly flow.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
KEY MESSAGES:

- Uncertainty increases greatly for the end of the week with
  Tropical Storm Helene.
- Rain chances will continue through the end of the week.
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The central CONUS trough may interact with Tropical Storm Helene as
it moves inland out of the Gulf. Meanwhile, the northern stream
trough will be sliding across the Northeast states. Ensemble
clusters all show that the remnants will be absorbed by the
trough but with much uncertainty after that.

The highest probability scenario at this time is that the northern
stream trough deflects the remnants off to our west and rain chances
stay low.

There are potentially wetter solutions with a track further
east; one of the members depicts 2-3 inches of rain with this
outcome. However, there is a 10% chance of exceeding 2 inches of
rain in 24 hours with 13Z NBM run. If impacts do evolve from
Helene, it would likely be Friday into Saturday.

By Monday into Tuesday, the remnants of an upper-level low
associated with Helene will weaken near our southwest of the
Ohio River Valley and drift east as a trough over the Dakotas
ejects southeast.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
Scattered showers will continue to cross the area through the
evening and into the early overnight. Some minor instances of
restrictions are possible through the evening.

Deteriorating conditions are expected late tonight into
Wednesday morning with ensemble guidance suggesting a greater
than 70% chance of MVFR cigs (30-50% chance of IFR) at all
terminals by or shortly after sunrise. Additionally, any
locations that saw heavy rain today will likely see some amount
of fog development overnight, further impacting flight
categories at area airports through sunrise.

Another round of showers and thunderstorms are expected through
dawn and through midday. This will impact cigs through the
coming day as well. Expect intermittent restrictions through
the day tomorrow with passing thunderstorms.

.Outlook...
Some improvement is expected Wednesday, with a 80% chance of
VFR everywhere except FKL/DUJ, though very isolated showers and
storms may bring temporary cig/vis drops. Widespread restriction
chances increase again Thursday morning, before VFR returns to
close out the work week.
-- End Changed Discussion --

&&

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

&&

$$

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