-- Discussion containing changed information from previous version are highlighted. --
905
FXUS61 KPBZ 191824
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
224 PM EDT Wed Jun 19 2024

.SYNOPSIS...
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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.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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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.
-------------------------------------------------------------------

The ridge aloft will shift a bit further south today with the axis
extending back to the west and into the southern portions of the
forecast area. As a result, heights will modestly rise and this will
likely be enough to keep convection to a minimum across most of our
area. Cirrus coverage through the morning has precluded a lot of our
area from reaching convective temperatures yet, but some cumulus are
starting to pop along the ridges. Hi res ensemble probabilities and
latest CAMs favor development along the lake breeze and a
differential heating zone in north central Ohio where the cirrus
has scattered out, so coverage in our area should be less than
the past two days and confined north and west of Pittsburgh.
Where any storms can materialize, the threat will once again be
damaging winds from downbursts with up to 1300 J/kg of DCAPE,
2500-3000 J/kg MLCAPE, and up to 30 knots of effective shear
present on mesoanalysis. Storms should begin to pop after 18z to
our northwest with outflow boundaries keeping convection going
through the day. A Marginal Risk (1/5) remains in place north of
Pittsburgh. Precipitable water values remain above 1.5",
highest to the north, so localized heavy rainfall under
persistent thunderstorms is again possible.

Once again, expect heat indices to cross the 100 degree mark this
afternoon, especially in the urban areas and east of Pittsburgh as
aforementioned cirrus coverage has muted heating a bit across
eastern Ohio and western Pennsylvania. Heading into the overnight,
convection should wane by 00z. Localized patches of fog will be
possible again tonight and most likely in the river valleys.
Low temps tonight will once again be in the lower 70s to mid 70s
allowing for little relief from the heat overnight.
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&&

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

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

Less upper cloud coverage on Thursday and Friday will allow for
highs to reach back into the mid 90s and a 70-80% chance of >95
degrees, highest in the urban areas and valleys. Highs will
climb by a few degrees into Saturday with probabilities
indicating Saturday may be the hottest. Some records may be
challenged. With dew points still in the upper 60s/low 70s, heat
index values will remain around or above 100 degrees. 50-80%
chance of lows >70 will continue to provide little relief from
the heat at night. Considering heat effects will be cumulative,
late week looks compoundingly dangerous. The early season
event, and temperatures increasing slightly each day, will
exacerbate any existing heat issues.

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.

Weak upper waves on the northern periphery of the 596-598 dm ridge,
along with a lake breeze, may again allow for some pop up
thunderstorms in the afternoon both days. Best chances Thursday will
be Pittsburgh and north, potentially slightly further south on
Friday, based on latest hi res ensemble guidance with a similar
environment to Wednesday with a 60-90% chance of >1000 J/kg of CAPE.
Weaker flow aloft 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.
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&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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KEY MESSAGES:

- Heat continues into Saturday and heat headlines have been extended
  through Saturday evening.
- Relief from the heat favored with a passing trough over the Great
  Lakes Sunday into Monday.
- A weaker ridge builds in after Monday.
-------------------------------------------------------------------

The upper ridge will begin to retrograde on Saturday but still hold
strong enough for one more day providing a continuation of the
dangerous heat, and perhaps the hottest day. Ensemble 850 mb
temperatures still remain in the 22-24C range and even the NBM
10th percentile suggests low to mid 90s. 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 have been extended through Saturday. That said,
some subtle weaknesses in the flow as the ridge axis pulls south
and allow for isolated to scattered afternoon convection to
throw wrinkles in the heat, but predictability in coverage and
location is low probability.

Come Sunday into Monday, the ridge retrogrades with ensemble
clusters showing respectable agreement on an upper trough
pushing down through the Great Lakes and 500 mb heights
decreasing up to 10 dm by Monday. Surface high pressure migrates
off to the east ahead of low pressure associated with the upper
trough that drags to our north, but some timing differences
with it lend lower confidence. Ensemble precipitation chances
increase overnight Sunday into Monday as a cold front may drag
through during that timeframe. Upper ridging is then favored to
build back in by mid week with highs again potentially
increasing to above 90 degrees, but heights don`t look quite as
extreme as this week.
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&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Thunderstorms continue to look less likely this afternoon as
warm air aloft (indicated by latest aircraft obs and rapid
update soundings) should keep convection largely capped off.

Winds remain light and variable with a generally southerly
component.

.Outlook...
High probability for VFR and dry weather through the week as
strong ridging develops aloft. Restrictions with rain may return
late this weekend with a cold front.

&&

.CLIMATE...
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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:

Wednesday, June 19th
Pittsburgh, PA:       97F  (1994)     74F  (1905)
Wheeling, WV:         95F  (1933)     70F  (2021)
Morgantown, WV:       94F  (1994)     72F  (2018)
New Philadelphia, OH: 92F  (1994)     70F  (2018)
Zanesville, OH:       94F  (1994)     75F  (1897)
DuBois, PA:           87F  (2001)     66F  (1975)

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)
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&&

.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
LONG TERM...MLB
AVIATION...Rackley/Shallenberger/88
CLIMATE...MLB/SKH/CM