298
FXUS61 KPBZ 291558
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1158 AM EDT Sat Jun 29 2024

.SYNOPSIS...
The probability of severe weather increases after 12pm today.
Torrential rain, tornadoes and damaging wind all will be
possible.

&&

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

- Favorable environment for severe weather today. Damaging wind and
  tornadoes will be the main threat.
- Flash flooding will also be possible with heavy rainfall
  mainly from Pittsburgh metro and north.
-------------------------------------------------------------------

Low pressure currently moving across the upper Great Lakes has
resulted in broad and deep warm, very moist southerly flow
throughout the Ohio Valley and lower Great Lakes regions. A shield
of showers and thunderstorms to our west out ahead of a cold front
and with an attendant shortwave will arrive in our neck of the woods
after noontime today. Our severe weather threat will likely be tied
to this feature later this afternoon and evening.

The 12z PIT sounding supports the expected threats of damaging wind,
a few tornadoes, and heavy rainfall leading to flash flooding.
Notable elements on the sounding in regard to the flash flood threat
include a precipitable water value of 1.98" (above the daily
climatological max), warm cloud depths to around 14kft, and, above
the lowest 3 km or so, unidirectional west-southwest flow. Corfidi
propagation vectors of 10 knots or less across the area this morning
suggest slow moving and backbuilding potential with the convection
today. This, coupled with high PWATs even pushing 2.2" north of
I-80, signals a flash flood concern for roughly Pittsburgh and
north especially with any training showers and thunderstorms.
The latest hi res ensemble data supports a 60% chance of 1 hour
rainfall rates >0.5". Localized areas of 1-2" of rain aren`t
out of the question.

For the severe threat, despite morning cloud cover and showers,
temperatures are already in the mid 70s/low 80s, so
destabilization isn`t expected to be all that limited. Latest
ensemble joint probability is 60-90% for >1000 J/kg SBCAPE and
>30 kt of shear. Similar to the event this past week, the bulk
of the shear is packed into the lowest levels in the 25-35 knot
range which could support a tornado threat. Latest convective
models continue to suggest some organization into one or
multiple line segments that push across the area through the
afternoon and evening. The environment ahead of these storms
will support thunderstorm intensification to severe levels, with
damaging straight line wind and a few tornadoes being the
primary threat. The greatest tornado threat will reside
generally north of the I-70 corridor where 850mb and 700mb flow
will be stronger resulting in more bulk shear in the sfc-3km
layer and elongation of the low level hodographs. If any
discrete cells can fire ahead of the more organized segments,
deviation to a right moving motion vector of east/northeast will
be favorable for streamwise vorticity ingestation and increased
tornado potential. In addition, the bulk of the shear packed
into the lowest levels could also pose a QLCS tornado threat
with any bowing segments. Farther south, weaker winds and a more
unidirectional wind profile in the low levels appear to reduce
the tornado threat somewhat, though steep low level lapse rates
will still promote strong low level updrafts in thunderstorms
which can overcome the more marginal profiles as we`ve seen so
far this spring and summer, so the tornado threat certainly is
not zero in those areas. The Storm Prediction Center has
maintained a Slight Risk (Level 2 out of 5) for severe
thunderstorms across the entire area.

In terms of timing, the primary wave of thunderstorms carrying the
greatest severe threat pushes through between roughly 3-9pm, though
there is some indication of weak backbuilding occuring towards the
latter half of that window with storms lingering in areas south and
east of Pittsburgh until closer to midnight. Interestingly, some 12z
CAMs have backed off some on the threat today, though not entirely
buying this as those that do are struggling with resolution of the
upstream MCS and painting a much drier boundary layer with dew
points mixing out this afternoon which seems very low probability
given the moist southwest flow and morning rain.

Additionally, there may be redevelopment overnight into early Sunday
morning along the cold front itself as it pushes through the area.
Hi-res guidance suggests a low-end severe threat carries into this
overnight wave, though limiting factors will be a stabilizing
surface layer and available instability.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- A cold front sweeps through the area Sunday morning/afternoon.
- A few storms along the front could become strong, primarily
  east and south of the Pittsburgh metro. Damaging straight line
  winds will be the primary threat.
- Cooler and drier weather expected in the wake of the front
  Sunday night as high pressure builds into the region.
-------------------------------------------------------------------

A cold front enters the area from the northwest around or
shortly after sunrise on Sunday. Showers and thunderstorms could
be ongoing along the front itself as it pushes through, leading
to lingering rain chances across much of the area through the
morning hours. The front is not expected to exit to the
southeast until early to mid afternoon, which may allow enough
destabilization to occur ahead of it to support a few strong
thunderstorms that will carry a low-end damaging wind threat,
primarily east and south of the Pittsburgh metro. As such, the
Storm Prediction Center has highlighted the higher terrain of
southwest PA and much of northern WV in a Marginal Risk (Level
1 out of 5) for severe weather.

Drier air moves into the area in the wake of the front Sunday
evening and Sunday night, as well as cooler temperatures with
overnight lows dipping into the 50s areawide by early Monday
morning.

&&

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

- Dry weather expected Sunday through mid week under building
  high pressure.
- Showers and thunderstorms return Wednesday and Thursday with
  another low pressure system.
-------------------------------------------------------------------

Dry weather persists through Tuesday night under high pressure.
The upper ridge then pushes off to the east and low pressure
moves back into the Great Lakes region, bringing showers and
thunderstorms back to the area Wednesday through the end of the
week.

Temperatures will be below seasonal levels Monday, followed by a
warm up back to near or slightly above levels Tuesday through
the end of the week.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
Much of the forecast remains on track for the early morning
period with VFR expected with increasing mid-level cloud
coverage as a system approaches from the west, ushering in
warm/moist advection.

VFR will prevail with moderate to high probability for all
airports south of FKL/DUJ for the TAF period well into the warm
sector of the passing low. At DUJ/FKL, deeper saturation
maintains chances of MVFR for most of the day.

Beyond daybreak, shower chances slowly increase from northwest
to southeast as pre-frontal convergence is strewn across the
area. With increased daytime instability, shower chances
transition to storm chances in the afternoon/evening for all
ports.

Strong to severe thunderstorms are anticipated as the front
crosses the area, mainly after 18Z. The first ports to be affect
will likely be ZZV, BVI, and FKL. Storms are most likely to
finish at MGW around 02Z. The most likely timing for Pittsburgh
area ports is between 20Z and 22Z.

Low clouds and patchy fog are possible tomorrow night with cold
advection and radiative cooling forcing saturation, given
recent rainfall. IFR restrictions remain possible, most likely
for eastern ports.

.Outlook...
MVFR conditions may continue north of PIT with lingering low-
lvl moisture. Widespread VFR will likely return Sun afternoon
under high pressure and is likely to persist Mon and Tue.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch through late tonight for PAZ007>009-013>016-
     020>022-029-073-074-077-078.
OH...Flood Watch through late tonight for OHZ039>041-048>050.
WV...Flood Watch through late tonight for WVZ001-002.

&&

$$

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