712
FXUS61 KPBZ 240132
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
932 PM EDT Mon Sep 23 2024

.SYNOPSIS...
An active weather pattern is expected through most of the week
with a Marginal Risk for severe weather on Tuesday south of
Pittsburgh. Even with the clouds and threat of rain,
temperatures will remain warm through the week.

&&

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

- Isolated showers possible overnight
-------------------------------------------------------------------

A weak cold front/surface boundary was located across western
PA through northern WV. This front should gradually dissipate
tonight. Isolated showers were ahead of the front near FKL and
DUJ, and these should be slowly exiting the region tonight.
Another area of showers across central OH should continue to
dissipate as they approach the region. Most of the overnight
period should be dry, though another shortwave approaching the
Upper Ohio Valley region late tonight could result in a few
showers moving back in as moisture and ascent increase. Most of
this activity should hold off until Tuesday morning.

Clouds should limit the fog potential overnight, as low
temperatures remain around 10 degrees above average.

&&

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

- Rain chances continue through mid-week.
- Marginal Risk (1/5) for severe weather on Tuesday.
-------------------------------------------------------------------

Height falls ensue on Tuesday as the shortwave ridging is shunted
east by a digging central CONUS trough. Another center of low
pressure, this one perhaps slightly deeper than Monday`s, and
associated shortwave energy will track just off to our west. This
will bring another round of showers and thunderstorms. Deep layer
southerly flow will advect in much higher, Gulf source moisture with
ensemble mean precipitable water values in excess of 1.5" which is
above the 90th percentile of climatology.

A look at forecast soundings shows a deep warm cloud layer to ~13kft
with high equilibrium levels and skinny CAPE. This favors efficient
rainfall producers with warm rain processes. In addition, CAMs
continue to hint at potential localized areas of higher totals with
convective enhancement, but this is lower confidence. Hi res
ensemble probability for >1" through Tuesday night does show strips
of up to 40%, so the potential is there. Probability for at least
0.5" is between 40-80%.

In addition, a lower probability severe threat is also a
possibility. How much instability we can generate will be in
question with morning cloud cover and showers, and there won`t be
much mid-level dry air to work with owing to the saturated profile.
Ensemble probability of >1000 J/kg of CAPE maximizes in the WV
Panhandle/southeast OH, and northern WV at 40-60%. With dew points
in the mid 60s and forecast highs in the low 70s, LCLs will be low
and CAMs all show a veering low level wind profile as 850 mb flow
increases by afternoon atop backed southeasterly surface flow. This
presents a lower probability, conditional tornado threat. Machine
learning also suggests a low end wind and tornado threat, and we
remain outlined in a Marginal Risk (1/5) from Pittsburgh south.

The initial digging 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 shortwave and
general troughiness in southwest flow. 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.

&&

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

- Uncertainty increases greatly for the latter half of the week with
  potential tropical low interaction.
- Rain chances will continue through the end of the week.
-------------------------------------------------------------------

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. 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 /02Z TUESDAY THROUGH SATURDAY/...
Expect ample low level moisture to persist through the overnight
behind a weak frontal boundary and little advection. This will
give the potential for fog development overnight. The caveat is
with the lingering cloud cover and this may result into a more
stratus layer overnight resulting in IFR and below conditions.

Showers and thunderstorms will become more numerous towards
dawn and begin to move into the Ohio counties after dawn. have
put PROB30s in to account for the uncertainty in coverage. There
is expected to be another round developing towards the 16Z and
18Z period with additional convection continuing through 20Z.
Restrictions are expected to be IFR and below at times through
the morning and into the early afternoon, especially near
thunderstorms.

.Outlook...
Rain and restriction chance continues into Tuesday with another
low pressure center. Unsettled weather is then possible through
mid-week.

&&

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

&&

$$

SYNOPSIS...22/MLB
NEAR TERM...WM
SHORT TERM...MLB
LONG TERM...MLB
AVIATION...Hefferan/Shallenberger