-- Discussion containing changed information from previous version are highlighted. --
936
FXUS61 KPBZ 212011
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
411 PM EDT Fri Jun 21 2024

.SYNOPSIS...
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A dangerous heat wave will impact the region into the weekend.
A Heat Advisory and Excessive Heat Warning are in effect through
Saturday. Daily thunderstorms may pose a damaging wind threat
through the weekend.
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&&

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

- Dangerous heat continues through Saturday with little relief at
  night.
- Excessive Heat Warning and Heat Advisory remain in effect
  through Saturday.
- Showers and thunderstorms are possible each afternoon, a few
  of which could become strong.
-------------------------------------------------------------------

Latest visible satellite imagery shows a diurnal cu field across
much of the area this afternoon as temperatures have climbed
into the low 90s and dewpoints ranging from low/mid 60s to
around 70. Showers and thunderstorms have started to form within
a plume of better low-level moisture over eastern Ohio, with the
greatest concentration along a lake breeze advancing slowly
southeastward from the shore of Lake Erie into NE OH and NW PA.
As temperatures continue to climb this afternoon and the
moisture plume creeps eastward, expect storms to follow suit and
drift east into western PA. Recent ACARS soundings at PIT show
only around 1000 J/kg SBCAPE. However, at this time PIT is
located within a narrow corridor of drier boundary layer air,
which is likely limiting SBCAPE and therefore underrepresenting
actual instability across the rest of the area. In fact, the
18Z RAP analysis suggests upwards of 3000 J/kg SBCAPE in the
moisture- rich environment currently over eastern OH. This
amount of instability, coupled with weak but non-zero deep-layer
flow, could allow a few storms to strengthen to the point that
they pose a low-end damaging wind and hail threat.

Storms will begin to taper off around or shortly after sunset
with the loss of daytime heating, giving way to a rain-free
forecast overnight tonight. Temperatures continue to run warm
tonight, as has been the case all week, with lows remaining in
the upper 60s to low 70s.

More of the same is anticipated on Saturday as temperatures
climb back into the low 90s and isolated showers and storms
develop by the late morning or afternoon. Similar to today,
those storms will also carry a low-end threat for damaging
winds and hail.
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&&

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


- Relief from the heat favored with a passing trough over the Great
  Lakes Sunday into Monday.
- Cold front will return precipitation chances as well as a
  severe potential Sunday into Sunday night.
-------------------------------------------------------------------

Warm overnight temperatures are expected once again Saturday
night, with the NBM actually suggesting it may be the warmest
night of the past week, at least for eastern OH and areas within
the Ohio River valley in western PA and the northern WV
panhandle. Latest probabilities for low temperatures to remain
above 70F are >90% in those areas, as well as a 30-50% chance
of lows remaining 75F or higher. The good news is Saturday night
should be the final night with overnight temps this warm. By
Sunday, the pattern that has plagued us all week finally begins
to shift as the ridge over the region flattens and pushes
south, giving way to zonal flow and opening the door for weak
troughing to develop as low pressure moves into southern
Ontario.

This pattern shift will allow the first solid cold front in
quite awhile to drop southeast across the Great Lakes and Upper
OH Valley. Current timing has the cold front approaching the
area Sunday evening, allowing for plenty of heating and
destabilization to occur ahead of it during the afternoon.
Convective models do suggest a morning wave of showers moving
through the area, perhaps associated with a pre-frontal trough,
that may serve to disrupt or delay heating. However, given how
efficient heating can be this time of year, it wouldn`t take
much sunshine to develop at least marginal instability ahead of
the front. NBM probabilities for 1000 J/kg SBCAPE continue to
run around 70-90% generally near and west/northwest of
Pittsburgh, with lower (40-60%) probabilities farther southeast.

More concerning are model-derived soundings and hodographs which
suggest a fair amount of instability and wind shear being
packed in the sfc-3km layer due to steep low-level lapse rates
and a 40-50 knot 850mb jet that overspreads the area ahead of
the front. This latter feature, when coupled with more backed
surface winds and an almost due-east mature storm motion,
would lead to a decent amount of streamwise vorticity ingest
for any storms that are able to organize and deviate from the
mean flow.

All of the above factors combined, there is growing concern
regarding severe weather potential on Sunday (particularly
damaging winds and possibly a tornado or two). We will need to
keep a close eye on how the environment evolves. Possible
complications include morning convection limiting daytime
instability and forcing being focused along the front leading to
a linear storm mode. At this time, the Storm Prediction Center
has our entire area highlighted under a Marginal Risk (level 1
out of 5) for severe weather.

The front moves through Sunday night but a low chance for
showers and storms will continue behind the front mainly over
the ridges to the east as weak upslope flow and a lingering
post-frontal trough act to locally maintain ascent in those
areas.
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&&

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

- Relief from the heat favored with a passing trough over the
  Great Lakes Sunday into Monday.
- A weaker ridge builds in Monday night leading to drier and
  quieter weather on Tuesday.
- Active weather returns Wednesday and Thursday.
-------------------------------------------------------------------

There is a low chance for convection over the ridges to linger
into Monday afternoon due to a post-frontal trough that will be
slow to depart, however severe weather currently appears
unlikely. A weak ridge briefly builds over the area Monday
night, leading to quiet weather Tuesday and Tuesday night.
Temperatures are expected to rise into the upper 80s to lower
90s again on Tuesday, but early ensemble indications suggest
this heat won`t be as oppressive as the past week. A series of
weak shortwave troughs then pass over the area through midweek,
bringing showers and thunderstorms back to the forecast
Wednesday and Thursday before high pressure builds back in again
and dries us out Friday into the following weekend.
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&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
VFR is expected for the majority of the TAF period at most
airports. The exception is FKL, MGW and HLG, where they will
likely see some early morning MVFR fog.

A weak surface boundary dropping south along with 1000-2000
j/kg of CAPE will trigger storms this afternoon. Wind flow aloft
is light, though dry mid level air will create a damaging wind
threat with any storm that becomes organized. The timing,
coverage and location are still uncertain, precluding more than
a VCTS inclusion in the TAFs at this time.

Storms and the cu layer should dissipate this evening with the
loss of heating.

.Outlook...
Mainly VFR is expected through Saturday night, outside of
isolated afternoon and evening thunderstorms on Saturday.
Restrictions are likely Sunday, along with showers and
thunderstorms, as a cold front crosses the region. VFR is then
expected again Sunday night through Tuesday under high pressure.

&&

.CLIMATE...
The area has the potential to break various heat-related
records.

There is low probability that climate sites approach the
highest temperatures recorded in the 21st century:

Pittsburgh, PA:       98F  (7/7/2012)
Wheeling, WV:         98F  (7/7/2012)
Morgantown, WV:       101F (7/7/2012)
New Philadelphia, OH: 101F (7/7/2012)
Zanesville, OH:       101F (7/7/2012)
DuBois, PA:           101F (7/22/2011)

There is a modest probability many June all-time temperature
records may be at stake:

PIT: 98F (1988)
HLG: 100F (1933)
MGW: 99F (1893)
PHD: 99F (1988)
ZZV: 101F (1988,1934)
DUJ: 92F (1969)  *RECORD TIED ON 6/18/24*

Daily high maximum (left) and high minimum (right) temperature
records are at stake for:

Friday, June 21st
Pittsburgh, PA:       95F  (1933)     73F  (1934)
Wheeling, WV:         99F  (1933)     69F  (2016)
Morgantown, WV:       95F  (1953)     72F  (1988)
New Philadelphia, OH: 94F  (1994)     72F  (2016)
Zanesville, OH:       97F  (1988)     72F  (1997)
DuBois, PA:           89F  (1991)     68F  (1988)

Saturday, June 22nd
Pittsburgh, PA:       98F  (1988)     75F  (1988)
Wheeling, WV:         95F  (1923)     72F  (2011)
Morgantown, WV:       96F  (1923,1988)73F  (1988)
New Philadelphia, OH: 97F  (1988)     71F  (1997)
Zanesville, OH:       99F  (1988)     71F  (1997)
DuBois, PA:           91F  (2022)     68F  (2022)

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory until 8 PM EDT Saturday for PAZ007>009-013-015-
     016-022-031-074-076>078.
     Excessive Heat Warning until 8 PM EDT Saturday for PAZ014-020-
     021-029-073-075.
OH...Heat Advisory until 8 PM EDT Saturday for OHZ039>041-048>050-
     057>059-068-069.
WV...Heat Advisory until 8 PM EDT Saturday for WVZ001>004-012-021-
     509>511.

&&

$$

SYNOPSIS...Cermak
NEAR TERM...Cermak
SHORT TERM...Cermak
LONG TERM...Cermak
AVIATION...WM/88
CLIMATE...CM