437
FXUS61 KPBZ 201805
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
205 PM EDT Thu Jun 20 2024

.SYNOPSIS...
A dangerous heat wave will impact the region this week. A Heat
Advisory and Excessive Heat Warning are in effect through Saturday.
This event is highly unusual for our region and could be worse
than the 1994 heat wave. Isolated afternoon thunderstorms may
pose a damaging wind threat.

&&

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

- Excessive Heat Warning for the urban areas of western PA;
  Heat Advisory continues elsewhere.
- Heat index values ranging from 100F to 110F.
- Isolated to scattered thunderstorms possible again this afternoon
  with downbursts the primary threat.
-------------------------------------------------------------------

Less upper cloud coverage today has allowed temperatures to climb 4-
8 degrees warmer at noontime than those of 24 hours ago. As a
result, cumulus have popped across the area with the
achievement of convective temperatures. Thunderstorm-wise, we
again are going to need a trigger as the DCAPE is in place with
1200 J/kg overlaid on 1500-2000 J/kg of uncapped MLCAPE. This
will likely have to be the lake breeze or any remnant boundary
settled across the area as upper waves visible on water vapor
satellite on the northern periphery of the 596-598 dm ridge are
off to our north. Weaker deep layer flow today (~10 kt 850-300
mb mean wind) may result in slow moving storms with localized
heavy rainfall. Hi res ensemble paintballs favor north of
Pittsburgh with downbursts again the threat, but these weakly
forced setups are often handled poorly by CAMs. The northern
half of our area remains in a Marginal Risk (1/5).

Highs are favored to reach back into the low to mid 90s and a 50-60%
chance of >95 degrees, highest in the urban areas and valleys. With
dew points still in the upper 60s/low 70s, heat index values will
remain around or above 100 degrees. A 50-70% chance of lows >70
tonight will continue to provide little relief from the heat.

Potential impacts include heightened heat-related illnesses and
power grid issues with increased demand. It is strongly encouraged
to know where cooling shelters are located and stay hydrated. There
may be little relief at night. Make a list of friends and family to
check on and help them prepare. Prolonged exposure to excessive heat
was the primary cause of weather-related fatalities in 2023. For our
region, this heat wave may be compared to our worse than June of
1994. Please see the Climate section below for more numerical
details on the kinds of records that may be in jeopardy.

Convection will wane after sunset and give way to a warm, muggy
overnight period. Light wind and mostly clear skies may again
allow for patchy fog development in the river valleys; hi res
ensemble probabilities for visibility restrictions are 30-50%.

&&

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

- Dangerous heat continues through Saturday with little relief at
  night.
- Excessive Heat Warning and Heat Advisory remain in effect through
  Saturday.
- Slight chance of thunderstorms in the afternoons.
-------------------------------------------------------------------

Weak upper waves on the northern periphery of the 592-594 dm ridge,
along with a lake breeze, may again allow for some pop up
thunderstorms in the afternoon on Friday. With some weak flattening
of the ridge axis, storms may be able to infiltrate more of the
area, but confidence in these days is low as CAMs struggle with
weakly forced environments. Latest hi res ensemble guidance
shows a similar environment with a 60-90% chance of >1000 J/kg
of CAPE. Weaker deep layer flow underneath the ridge similar to
Thursday may keep shear values slightly less in the 15-20 kt
range. This would still be sufficient for scattered storms
capable of downbursts with modeled DCAPE >1000 J/kg.

The upper ridge will then begin to retrograde slowly on Saturday but
still hold strong enough for one more day providing a continuation
of the dangerous heat, and perhaps the hottest day with even the NBM
25th percentile suggesting mid 90s. Ensemble 850 mb temperatures
still remain in the 22-24C range. Some records may be challenged.
Due to the compounding effects, continued heat indices at and above
100 degrees, and the WPC heat risk tool showing major to extreme
impacts, the heat headlines remain in effect through Saturday.
That said, as with the past several days, some subtle weaknesses in
the flow as the ridge axis pulls south could allow for isolated to
scattered afternoon convection to throw wrinkles in the heat, but
predictability in coverage and location is low probability at this
time range.

With high confidence in lows remaining >70, this will provide little
relief from the heat at night. Considering heat effects will be
cumulative, this late week into the weekend looks compoundingly
dangerous. The early season event, and temperatures increasing
slightly each day, will exacerbate any existing heat issues.

&&

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

- Relief from the heat favored with a passing trough over the Great
  Lakes Sunday into Monday.
- Cold front may return precipitation chances Sunday night.
- A weaker ridge builds in after Monday.
-------------------------------------------------------------------

Come Sunday into Monday, the upper ridge will shunt south as a
trough approaches from the northwest and slides through the Great
Lakes. This will provide a reprieve from the extended period of
extreme heat. Ensemble clusters indicate the approach of the
trough and the passing of a cold front sometime late Sunday into
Monday morning. General probability of rain increases along the
boundary but slight disagreement on the strength and timing
lends slightly lower confidence. Machine Learning hits the area
for potential severe storms if the timing of the frontal passage
is favorable. Northwest flow events always bare watching around
here, especially with a cold front pushing through 70s dew
points. Decreasing heights from 585dm Saturday to 579dm by
Monday morning support slightly cooler temperatures.

Quieter conditions expected into Tuesday as a flat ridge begins to
build over the Plains and surface high starts to develop around the
Great Lakes as heights begin to rise. Temperatures are expected to
rise into the upper 80s to lower 90s but early ensemble indications
are that it won`t be as oppressive as the past week`s event.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
VFR conditions and light/calm wind will continue as high
pressure remains the dominant feature across the region. Have
kept TSRA mention out of TAFs with no apparent trigger to
initiate convection in latest guidance or obs. Best chance
would be FKL if convection develops along an area of lake-
breeze convergence.

.Outlook...
Mainly VFR and dry weather will continue outside of any isolated
thunderstorms. Restrictions with rain may return late this
weekend with a cold front.

&&

.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:

Thursday, June 20th
Pittsburgh, PA:       95F  (1994)     78F  (1924)
Wheeling, WV:         97F  (1933)     70F  (1924)
Morgantown, WV:       99F  (1893)     75F  (1924)
New Philadelphia, OH: 95F  (1994)     71F  (2009)
Zanesville, OH:       98F  (1934)     75F  (1924)
DuBois, PA:           89F  (1991)     66F  (1996)

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...MLB/Shallenberger
NEAR TERM...MLB
SHORT TERM...MLB/Shallenberger
LONG TERM...MLB/MAM
AVIATION...88
CLIMATE...MLB/SKH/CM