209
FXUS61 KPBZ 070033 AAA
AFDPBZ

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
833 PM EDT Mon May 6 2024

.SYNOPSIS...
A muggy night, with patchy fog in some areas, is expected
overnight. Severe weather potential increases Tuesday evening,
after 6pm and could last into the overnight hours.

&&

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

- Fog will be possible late tonight in the wake of afternoon
  showers and storms, especially south of Pittsburgh

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A line of showers and storms in central WV will advance ewd
this evening, and the lingering couple of showers currently
north of this coherent line will trend toward dissipation this
evening as broad upper support for convection wanes. With
dewpoints quite high around 60F south of a BVI-IDI line, fog
will be likely late tonight as the airmass stagnates.

Probability of fog (less than a half a mile in visibility)
ranges from 45% to 65% for areas south of I-70 in the 2a-8a
timeframe, and probability of visibility less than one-quarter
mile is in the 40-50% range. A Dense Fog Advisory may need to
be issued for forecast zones south of Pittsburgh tonight but
will continue to monitor at this time, as dry air invading from
the north amid building high pressure may complicate the
evolution of the airmass.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
KEY MESSAGES:

- A passing warm front from the west will increase the risk of
  severe storms late Tuesday evening into early Wednesday
  morning
- Hail, damaging wind, tornadoes, and flooding could occur with
  the passing disturbance
- Highest probability for severe weather is in eastern Ohio
- Ridging over the Great Lakes is expected to reduce
  precipitation chances briefly Wednesday afternoon/evening

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

A strong low pressure system, which is impacting the Great
Plains today, is expected to eject into the northern Plains/Dakotas
on Tue. With a closed upper-lvl low positioned north over
Newfoundland and the low to our northwest, ridging is expected
to build briefly over the Great Lakes. Therefore, Tue is
expected to stay mostly dry in the morning/early afternoon. A
few stray showers may develop after 3pm Tue as the ridge axis
quickly breaks down as a new surface low forms along a warm
front in the Midwest.

The timing of severe weather is expected to be between 7pm
Tuesday and 2am Wednesday. Despite the loss of sfc heating, the
surge of warm, moist air from the south from a developing and
progressing low-level jet will keep the region very unstable.
Little to no CIN, and MLCAPE of 1000-1500 J/kg, are expected
during the overnight time period. Effective shear will range
from 45kt to 50kts and will support well-organized storms. Hail,
tornadoes, and damaging winds are all possible with this
passing disturbance. Very large hail (2+ inches, larger than a
golf ball) may form in storms that have strong reflectivity
above 25kft to 30kft, based on model soundings given a deep
layer of drier air above 500mb to 300mb.

The potential of severe storms decreases after 2am Wed morning
as mid-level ridging builds.

&&

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

- A new disturbance is expected to produce severe storms early
  Thu morning
- Model ensembles suggest a very wet pattern into the weekend
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Our region will continue to remain in an active weather pattern
as a new low pressure system forms over the Great Plains early
Wed, tracks east, and enters the Ohio River Valley early
Thu morning. Severe storms could produce damaging wind, and/or
tornadoes due to high shear and MUCAPE of 500-1200 J/kg. The
low-level jet will likely be stronger than the Tue night
disturbance. Hi-Res guidance suggests 850mb wind of 55-65 kt
could be present.

A passing cold front may stir additional severe storms Thu
afternoon southeast of Pittsburgh. However, the main threat will
likely reside over the eastern CONUS (noted in SPC`s Day 4
Outlook).


Model ensembles project a pattern shift late week as an
elongated trough builds over the Great Lakes. Below-average
temperature is likely Fri through Sun within northwesterly
flow, and 850mb temperature could range from 2C to -1C. At the
moment, the potential for frost/freeze concerns is considered
low.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
High pressure centered north of Lake Erie will continue to
promote VFR conditions for a majority of the region through much
of the TAF period even as its slides toward upper NY. The
notable aspects within it will be the encroachment of a warm
front well south of the region that may nudge MVFR to localized
IFR cigs to southern terminals (ZZV/MGW) Tuesday morning.
Additionally, diurnal heating is expected to promote bkn VFR cu
through the afternoon (with a brief window of MVFR with cu
initialization).

Broad but weak 700mb ascent coupled with moist advection within
SW flow will maintain at least low probability showers (lower
prob lightning) throughout the TAF period. However, timing of
convection remains too difficult to pinpoint given weak forcing;
only notable mention outside of a VCSH is at KMGW due to closer
proximity to any potential shortwave moving within the 700mb
flow.

Showers and thunderstorms will increase in probability Tuesday
afternoon and evening. The first line along a pre- frontal
trough should dissipate/decay before reaching much of eastern OH
between 21z-00z. The higher confidence line should move through
the region between 02z-08z; be prepared for gusty wind and cloud
to ground lightning with that convection.

.Outlook...
The active weather pattern will persist through the end of the
week by promoting periods of showers and thunderstorms.

&&

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

&&

$$

SYNOPSIS...Kramar/Hefferan
NEAR TERM...Kramar/Hefferan
SHORT TERM...Hefferan/Kramar
LONG TERM...Hefferan/Kramar
AVIATION...Frazier