-- Discussion containing changed information from previous version are highlighted. --
408
FXUS61 KPBZ 210550
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
150 AM EDT Fri Jun 21 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 /UNTIL 6 AM THIS MORNING/...
KEY MESSAGES:

- Excessive Heat Warning for the urban areas of western PA;
  Heat Advisory continues elsewhere.

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

Happy Astronomical summer to those who celebrate. Despite sun
angles being at their absolute maximum, convection today was
lack- luster. A few updrafts in the vicinity of Pittsburgh
related to urban-heating influences and north of I-80 put down a
cold pool; these are expected to linger in weak flow. 20k-22k
storm tops did not realize the full 1100 J/kg DCAPE. The outflow
undercut the convection, and further showers and storms
diminished. As we continue into the evening and overnight, the
environment will continue to be come less favorable, but there
is still a low probability of updraft development on the outflow
boundary that will need to be monitored through sunset. Not
much change was made to the overnight forecast, lows near or
above 70.

.. Previous Discussion ..

A 50-70% chance of lows >70 tonight will continue to provide
little relief from the heat. 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 /6 AM THIS MORNING 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.

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.

&&

.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 /05Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
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.

The CU rule and model soundings indicate a scattered to broken
cumulus layer will develop by mid morning. A weak surface
bo9undary is expected to drop southward this afternoon. Model
ensemble output shows 1000-2000 j/kg of CAPE as the boundary
moves through. 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.
-- End Changed Discussion --

&&

.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/Milcarek
SHORT TERM...MLB/Milcarek/Shallenberger
LONG TERM...MLB
AVIATION...WM
CLIMATE...MLB/SKH/Milcarek