067
FXUS61 KPBZ 290755
AFDPBZ

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

.SYNOPSIS...
Showers and thunderstorms expected today and tonight. The
probability of severe weather increases this afternoon and
evening. Torrential rain, tornadoes and damaging wind all will
be possible.

&&

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

- Showers and thunderstorms expected, a few of which may become
  strong to severe. Primary threats are damaging straight line
  winds and possibly a tornado or two.
- Flash flooding will also be possible due to torrential
  downpours in the heavier thunderstorms, mainly from the
  Pittsburgh metro on north.

------------------------------------------------------------------

Low pressure currently located over the upper Great Lakes has
resulted in a broad region of southerly flow setting up across
the Ohio Valley and lower Great Lakes regions. This has been
ushering a warm and moist airmass northward, effectively helping
to moisten not only the surface (dewpoints up roughly 10
degrees from where they were this time yesterday), but the
deeper-layer profile as well. Very dry air was still noted on
the PIT 00Z sounding in the 700mb-600mb layer, which has helped
limit (via evaporation/entrainment) the vertical extent of
attempted showers across our area thus far, despite there being
plenty of instability. As a result, much of the shower activity
has developed to our north and west for now. However, that dry
layer will eventually moisten and convection should then expand
southward and eastward into our forecast area by dawn, filling
in across eastern OH and northwest PA (generally north and west
of Pittsburgh). A roughly southwest-to-northeast motion may
result in training of showers and storms across these areas
throughout the morning, which combined with impressive deep-
layer moisture profiles characterized by 2+ inch PWATs, may
lead to some flooding issues. A Flash Flood Watch remains in
effect for areas north of I-70 until 2AM tonight.

Gradually, showers and storms shift eastward, with convective
models continuing 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 winds 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. Farther south, weaker
winds and a unidirectional wind profile in the low levels appear
to reduced the tornado threat somewhat, though steep lapse
rates will still promote strong low-level updrafts in
thunderstorms which can overcome marginal shear profiles, 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 southeast of Pittsburgh until closer to Midnight.
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 available instability
will be heavily dependent upon how worked over the environment
is following the evening round of storms and whether enough
recovery can occur through warm air advection alone.

&&

.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 /07Z 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. SHowers remain most likely for ZZV before
sunrise.

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 from 8 AM EDT this morning through late tonight
     for PAZ007>009-013>016-020>022-029-073-074-077-078.
OH...Flood Watch from 8 AM EDT this morning through late tonight
     for OHZ039>041-048>050.
WV...Flood Watch from 8 AM EDT this morning through late tonight
     for WVZ001-002.

&&

$$

SYNOPSIS...Cermak
NEAR TERM...Cermak
SHORT TERM...Cermak
LONG TERM...Cermak
AVIATION...Milcarek