-- Discussion containing changed information from previous version are highlighted. --
564
FXUS61 KPBZ 162010
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
410 PM EDT Sun Jun 16 2024

.SYNOPSIS...
A prolonged and potentially dangerous heat wave is anticipated
this week. A Heat Excessive Watch is in effect Monday through
Friday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
-- Changed Discussion --
KEY MESSAGES:

- Today begins the first day of abnormally warm weather as ridge
  axis builds across the East Coast.

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

Dry, quiet, and warm weather underway today as ridge axis,
currently situated over the Southeast, extends north. Deep
mixing of dry warm air will prompt temperatures in eastern
OH/northern WV to peak near 90F today. Probability of ZZV/MGW
reaching >= 90F ranges between 60% to 70%.

Southerly flow has counteracted mixing into a pretty dry
boundary layer and kept dew points steady, if not rising by a
degree or two, this afternoon. A deck of cumulus has developed
south of Pittsburgh where convective temperatures have been met.
Can`t entirely rule out a low probability pop up, likely
orographically driven, shower over the WV ridges through
sunset, but recent ACARS soundings from PIT suggest a stout warm
layer around 700 mb likely precluding lightning or significant
vertical growth. Otherwise, subsequent with the continuing light
southerly flow overnight, low temperatures will range in the
low to mid-60s, about 5 degrees above the climatological
average.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/...
KEY MESSAGES:

- The potential for record breaking heat is expected Monday
  into Tuesday, Excessive Heat Watch is in effect.
- Weak shortwave activity may stir isolated showers/storms late
  Monday afternoon
- If stronger storms develop, downbursts may prompt a damaging
  wind threat.

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

Ensembles have been consistent on the amplification of
a ridge on Monday, with 591dm building to the north of the
forecast area. The forecast headache Monday is the risk for cu
development and scattered showers and storms. Hi-Res guidance
suggest late afternoon convection. With sufficient instability,
surface based CAPE ranging between 2500J/kg to 3000J/kg under
strong surface heating and weak flow, strong downbursts could
develop between 3pm to 7pm Monday.

Latest NBM probs for measurable rainfall are generally 20 to
30% across the entire area Monday. This seems high when
factoring in everything working against convection. The ridges
may be the place to watch as the low-level flow would bring
orographic lift into the equation which could be enough to
overcome those limiting ingredients.

Therefore, if we do see an increase in clouds and/or perhaps
convection, this will obviously effect Mondays temperatures.
Coordination was made with surrounding offices to hold the
Excessive Heat Watch for Monday for now. In the next 12 hours,
a Heat Advisory may be issued for areas that have medium to high
confidence that dry conditions prevail.

The ridge will continue to amplify on Tuesday as we see heights
of 594dm-596dm across the region. 850mb temperatures continue
to rise as well as +18C to +20c spreads northward across the
entire forecast area. Still seeing indications of a shower/storm
threat Tuesday as more waves of energy rotate overtop of the
ridge. However, the NBM has shifted focus for activity on
Tuesday further north toward the I-80 corridor as everything is
forced northward due to the expanding 500mb heights. The story
for activity Tuesday remains the same as Monday, but the area
under the threat has decreased.

So what does that mean for temperatures Tuesday? With the
strengthening ridge and warming aloft, would think that cu
coverage, for most of the region, would decrease on Tuesday,
which should translate into hotter surface temperatures. This is
showing up in the NBM probabilities for highs >95 degrees.
Probs of 50-70% have spread across most of the region, outside
of the mountain tops and even starting to see probs of >98
degrees in low lying and rural areas. So this will be a building
heat that should increase from Monday into Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
KEY MESSAGES:

- High confidence in a dangerous heat wave holding through the
  week with major heat impacts possible.
- Excessive Heat Watch in effect through Friday.
- Seeing some timing differences on when the hottest air
  arrives.
-------------------------------------------------------------------

The numbers and timing of the most extreme heat continue to
evolve, but our overall expectations have not changed for this
period. We are looking at a potentially historic heat wave for
Pittsburgh and the Upper Ohio Valley, with impacts to public
health and utilities a possibility.

Model cluster analysis continues to paint a high-confidence picture
of the overall pattern. An anomalously strong 500 mb ridge will
persist over the eastern CONUS through Friday and possibly into
early Saturday, reaching its peak during the Wednesday/Thursday
period, before potentially becoming a bit more muted Sunday.
Both the EPS and GEFS means have 500mb heights of 597dm or
higher during that period. This sets the stage for a prolonged
period of high temperatures well into the 90s. NBM probabilities
of highs >95 increase and expand Wednesday through Friday to
50% to 90% for the region, with probabilities >100 confined to
30% to 50% in the valleys on Wednesday, but 30% to 50% for much
of the lowlands on Thursday and Friday. There is a possibility
that these values are underdone. Given the strength/position of
this ridge, precipitation chances and cloud development are
quite low, especially during the Wed- Fri period, which will
cause an increasing dry surface, promoting higher temperatures.
Further, dew points were nudged down a hair during the daytime
hours, and temperatures were raised slightly above the
deterministic NBM. Given that sun angles are at their annual
peak, insolation will add another warming factor via a super-
adiabatic surface layer. This will be a building heat, that
will slightly increase each day.

When considering dewpoints, heat index values in the 100 to 110
range are in the cards for a few days.  There does remain some
uncertainty in how widespread and long-lasting these kind of heat
index values will be from day to day. This normally has
implications for what kinds of heat-related headlines would be
appropriate. However, we feel that this event will have a length
and impact that the standard criteria may not capture. So the
Excessive Heat Watch will remain in place for the entire
forecast area Monday through Friday.

There are still uncertainties with the forecast. But signals
this impressive do not come around very often.

Considering heat effect will be cumulative, late week is looking
particularly dangerous. The early season event, near-record
temperatures, and temperatures increasing slightly each day will
compound 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. Gather food,
water and medication now. Make a list of friends and family to
check on and help them prepare. Strongly consider rescheduling
outdoor events. Prolonged exposure to excessive heat was the
primary cause of weather-related fatalities in 2023.

This certainly is increasing slightly that there will be some
relaxation to the heat by early next week, but any relaxation
will still leave temperatures well above average. In the
Saturday-Sunday timeframe, all clusters reflect some flattening
of the ridge, but disagree on the degree of flattening. Some
maintain zonal flow or perhaps even weak eastern troughing early
next week, but even the coolest scenarios have temperatures
around average to start next week. The warmest scenarios
maintain near-record heat. SHould we stay quasi-zonal into next
week, we may get slight relief, but there as a notable fraction
on ensemble guidance that redevelops eastern ridging. CPC
maintains a moderate risk of excessive heat through 6/24.

Please see the Climate section below for more numerical details on
the kinds of records that may be in jeopardy.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
VFR conditions and light winds prevail throughout the TAF period
under building high pressure. Winds will continue to veer from
southeast to south throughout the evening.

Weak shortwave activity may stir isolated showers/storms after
19Z Monday. However, weak flow prompts a low confidence for
terminal impacts.

.Outlook...
High probability for VFR and dry weather through the middle of
next week as strong ridging develops aloft.

The only variance may come with isolated afternoon convection
starting Monday, but upper ridging should suppress coverage and
potential initiation.

&&

.CLIMATE...
The area has the potential to break various heat-related
records. In this climate section, we will attempt to address
some of the higher-profile historical temperature records.

First, we cannot rule out that some sites approach all time
record high temperatures:

Pittsburgh, PA:       103F (7/16/1988, 8/6/1918, 7/10/1881)
Wheeling, WV:         106F (7/22/1934, 8/6/1918)
Morgantown, WV:       105F (8/26/1893)
New Philadelphia, OH: 102F (7/17/1988)
Zanesville, OH:       106F (7/14/1936, 7/25/1934)
DuBois, PA:           101F (07/22/2011)

There is modest 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)

Due to the how early in the summer this heat wave is, there
is a high probability many June all-time temperature records
may be at stake:

Pittsburgh, PA:       98F  (1988)
Wheeling, WV:         100F (1933)
Morgantown, WV:       99F  (1893)
New Philadelphia, OH: 99F  (1988)
Zanesville, OH:       101F (1988,1934)
DuBois, PA:           92F  (1969)

Due to the duration of the heat, sites will also approach records
for consecutive days greater than 95F (dates are the day the
streak ended):

Pittsburgh, PA:       6    (6/20/1994, 8/11/1900)
Wheeling, WV:         8    (7/15/1936)
Morgantown, WV:       9    (9/16/1997, 7/19/1892)
New Philadelphia, OH: 5    (7/27/2016, 7/10/1988)
Zanesville, OH:       9    (9/4/1953)
DuBois, PA:           3    (7/9/1988)

And it should go without question that daily high maximum (left)
and high minimum (right) temperature records are at stake for:

Monday, June 17th
Pittsburgh, PA:       95F  (1994)     75F  (1892)
Wheeling, WV:         99F  (1936)     69F  (2004)
Morgantown, WV:       95F  (1967)     72F  (1939)
New Philadelphia, OH: 95F  (1967)     69F  (2022)
Zanesville, OH:       99F  (1936)     72F  (1994)
DuBois, PA:           89F  (1994)     66F  (1892)

Tuesday, June 18th
Pittsburgh, PA:       97F  (1994)     73F  (1905)
Wheeling, WV:         95F  (1944)     71F  (2018)
Morgantown, WV:       95F  (1994)     70F  (2018)
New Philadelphia, OH: 95F  (1994)     72F  (2017)
Zanesville, OH:       99F  (1944)     73F  (1944)
DuBois, PA:           89F  (2018)     69F  (2018)

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)

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Excessive Heat Watch from Monday morning through Friday
     evening for PAZ007>009-013>016-020>022-029-031-073>078.
OH...Excessive Heat Watch from Monday morning through Friday
     evening for OHZ039>041-048>050-057>059-068-069.
WV...Excessive Heat Watch from Monday morning through Friday
     evening for WVZ001>004-012-021-509>514.

&&

$$

SYNOPSIS...Hefferan
NEAR TERM...Hefferan/MLB
SHORT TERM...Hefferan/22
LONG TERM...22/CL/Milcarek
AVIATION...Hefferan/Rackley
CLIMATE...