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034
FXUS61 KPBZ 241515
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1115 AM EDT Tue Sep 24 2024

.SYNOPSIS...
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A passing low pressure system may bring strong to severe storms
this evening, including tornadoes. A few areas may also
experience heavy rainfall that could prompt flash flooding.
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&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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KEY MESSAGES:

- Strong to severe storms are expected to increase in coverage southwest
  of Pittsburgh this afternoon/evening.
- Training thunderstorms may prompt flash flooding, especially
  in urban areas.
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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. The best
timing for strong to severe storms to form is between 1pm to
7pm.

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.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
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KEY MESSAGES:

- Rain chances continue through mid-week.

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The digging midwest trough is favored to cut off into a closed
low across the south-central CONUS with some uncertainty in the
timing and depth of a northern stream trough north of the Great
Lakes on Wednesday. Rain chances will continue with rounds of
shortwaves embedded with southwest flow aloft. With generally
weaker forcing, 24 hour totals ending Thursday morning look on
the lighter side, mostly less than 0.5", though a much lower
probability solution with a deeper, phased trough exists with
higher amounts.

Temperatures through mid-week will be cooler owing to increased
cloud coverage and precipitation.

A weak boundary may pass through the area sometime Thursday, but
seeing significant spread in the ensembles on the timing which will
impact when we lose the rain chances. Ensemble clusters exhibit
quite a bit of disagreement at this point with how the upper level
pattern evolves.
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&&

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

- Uncertainty increases greatly for the end of the week with
  potential tropical low interaction.
- Rain chances will continue through the end of the week.
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The central CONUS trough may interact with the remnants of now
PTC 9 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
here are lower. There are potential wetter solutions with a track
further east, but until we get a better idea on the evolution, will
stick with NBM given all of the uncertainty which advertises low end
rain chances into the weekend.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
Ample cloud coverage is expected to keep IFR visibility
restrictions to a minimum, but a brief drop to MVFR visibility
overnight cannot be ruled out with ample low-level moisture and
air near saturation, particularly for DUJ and perhaps FKL.
Winds are generally expected to remain light and out of the
southeast. A passing wave will allow for some light rain
locally, with more substantial amounts for MGW through sunrise.
Save FKL/DUJ, ceilings are generally expected to remain VFR
though brief drops in cigs to MVFR are possible in isolated
showers. As for FKL/DUJ, there is 40% to 60% chance of IFR cigs
and may continue through the period with continued rain chances.

Into today, convective coverage is expected to increase with
increasing instability. Flow will accelerate slightly out of the
southeast. Storms will remain possible through the day, but
TAFs attempted to capture the most favorable window for now.
The environment is supportive of damaging wind, hail, and
isolated tornadoes, but intensity is still highly questionable
with uncertainties in instability. Restrictions are likely in
any more intense storms. Uncertainties in instability and
mixing also truckle down to cigs, which may hover around the
VFR/MVFR range, depending on how much heating the area can tap
into during the day.

Deterioration is expected tonight, particularly for areas which
it has rained. Ceilings are expected to lower to the MVFR/IFR
range once again. Winds lighten out of the southeast.

.Outlook...
Some improvement is expected Wednesday, with a 80% chance of
VFR, though very isolated showers and storms may bring
temporary cig/vis drops. Restriction chances increase Thursday
morning, before VFR returns to close out the work-week.

&&

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

&&

$$

SYNOPSIS...Hefferan
NEAR TERM...Hefferan
SHORT TERM...22/MLB
LONG TERM...MLB
AVIATION...Milcarek