Flash Flood Warning 19, NWS Pittsburgh, PA

Area Forecast Discussion
National Weather Service Pittsburgh PA
749 PM EDT Wed Jul 26 2023

.SYNOPSIS...
Well above normal temperatures are expected through Saturday.
There will be periodic chances for showers and storms as we
remain under hot and humid conditions.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A thin line of showers and storms had developed across portions
of East Central Ohio, however, as the activity moved east, it
decayed rapidly. Latest forecast soundings show a capped
atmosphere over much of the region and the SPC mesoanalysis is
indicating a less buoyant atmosphere over the western half of
the region. Another area of showers and storms is moving quickly
across NE Ohio. This area should clip NW PA this evening. It too
is weakening as it moves eastward. Have updated the evening
PoPs to account for the decaying activity and to better time the
next line to our west.

Previous discussion...
Clouds will increase from the northwest this evening as a
mesoscale convective system (MCS) tracks through the Great Lakes
region this afternoon. Confidence is medium to high that
convection within western PA/northern West Virginia will remain
scarce through the late evening. A few select models suggest
isolated to scattered rain chances develop after 6pm in eastern
Ohio as the ridge starts to break down. However, confidence is
still low on that scenario.

A stronger signal for convection will likely form as a remnant
MCS, mentioned above, tracks across northern Ohio after 11pm.
Despite an increase of vertical wind shear, instability aloft
will exponentially decrease after midnight. The grand ensemble
of Hi- Res guidance suggest a mean value of CAPE at 11pm of
600-750J/kg in eastern Ohio before falling to 400J/kg by 2am.
Therefore, there could be a small window of opportunity of
strong wind gusts (between 45-50mph) for areas north of I-70 in
eastern Ohio (hence the "Marginal" issued by the Storm
Prediction Center) if the environment permits.

After midnight, the probability of strong to severe storms
decreases but the threat for heavy rainfall will slightly
increase for areas under training storms. PWAT values will
trend above the 90th percentile (which is 1.93" for 00Z July
27th at Pittsburgh, PA) and will support heavy rainfall rates
north of Pittsburgh through 6am.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/...
For Thursday morning, convection will likely be ongoing across
the region from the passing MCS mentioned in the near term.
A strong Theta-E boundary, which is noted with the NAM/RAP
analysis, may initiate additional convection mid-afternoon
south of Pittsburgh with diurnal heating. If updrafts have the
chance to overcome ridging in the low-lvls, strong downdrafts
may develop with noted dry aloft and enhanced DCAPE values over
1000J/kg. Therefore, a Marginal threat may need to be discussed
with Storm Prediction Center during the midnight update.

Otherwise, hot and humid conditions will continue across the
region at temperatures approach 90F and heat indices climb into
the upper-80s. Confidence for a Heat Advisory for Thursday is
still limited. The probability of exceeding 100F for the exceed
is ranging between 30 to 40 percent. If counties do need a Heat
Advisory, it will likely be Muskingum, Noble, Coshocton, and
Guernsey.

By Thursday night, the loss of surface heating will bring an
end to the showers and thunderstorms.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
* Key Message #1 - Hot weather Friday. Temperatures in the low
  to mid 90s and heat index values widespread around 100F
  outside of the mountains. A Heat Advisory is likely be issued
  for a large portion of the county warning area. An Excessive
  Heat Warning may be needed for a few Ohio counties.

* Key Message #2 - Strong to severe storms possible late Friday
  into early Saturday with a passing MCS. Damaging wind the
  primary impact.

An upper-lvl ridge will rebuild over the Ohio River Valley early
Friday into Friday afternoon. The low potential for showers and
storms and clearing conditions will cause temperatures to climb
into the mid-90s. Dangerous heat is anticipated Friday with
likely prompt a Heat Advisory at most; a few counties may need
an Excessive Heat Warning if the potential for heat index climbs
above 105F.

The potential for severe storms increases late Friday into
Saturday as numerous MCS's track through the Midwest and Great
Lakes 00Z Saturday through 00Z Sunday. With hot temperatures
building throughout the day Friday, instability will be
abundant; the NBM suggest the mean available CAPE will be above
2500J/kg. The worst case scenario suggest instability values
exceed 4000J/kg. Damaging wind gusts will likely be the main
concern with a prime environment. However, the confidence is
still low to medium on the lift mechanism. At the moment, the
Storm Prediction Center is holding a "Marginal" to highlight the
potential.

The ridge over the southern CONUS shifts west and centers over
the Desert Southwest on Sunday, transitioning deep- layer flow
over the local area to more northwesterly as the eastern
Canadian trough simultaneously becomes better established. As a
result of this shift, our local area sees temperatures return to
more seasonable levels (low 80s) and moisture profiles dry out,
which keeps us rain-free Sunday into early next week.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
First convective complex is keeping its impact near and north of
I-80, and will continue to do so through midnight until it
dissipates or departs by midnight. FKL stands to get a brief
bout of IFR visibility in heavier rain and gusty wind, and
included that as an early TEMPO. Other TAF sites will avoid
these early impacts and remain VFR through midnight.

Second complex, currently over far southern Michigan, will then
track towards the Upper Ohio Valley overnight, with impacts
possible between 05Z and 10Z. Some uncertainty remains with how
strong the complex is when it arrives and how long it will last
in the region before dissipation. Tried to add most likely
timing to TAFs, with prevailing thunder mainly confined to
locations near/NW of PIT. Brief periods of MVFR to IFR impact
will be possible in any storm, as will gusty wind.

MVFR ceilings may linger with a few showers in the wake of the
convection. After sunrise, VFR conditions will return as mixing
leads to a scattered to broken cumulus layer. Isolated
thunderstorms will be possible tomorrow afternoon in daytime
heating, and VCTS was used.

.OUTLOOK...
Additional thunderstorms are possible with a crossing cold
front Friday afternoon through Saturday, and some of these could
be severe.

&&

.CLIMATE...
Friday July 28th is on track to be the hottest day of 2023 so
far. It has not been that long since we reached highs in the
lower to mid 90s at our climate sites. Below is a table that
lists the last time they attained values we are forecasting.

Airport: Forecast High Friday - Last time reached

Pittsburgh: 94F - 6/22/22
Wheeling: 94F - 8/13/20
Morgantown: 95F - 6/22/22
Zanesville: 95F - 6/22/22
New Philadelphia: 95F 6/22/22
DuBois: 90F - 6/2/23

The new warmest minimum temperature on record could be set at a
few sites on July 27th and July 28th. Below are the numbers for
the 27th.

Record High Lows for July 27th (forecasted value)
Pittsburgh: 74F/1919 (74F)
Wheeling: 73F/2006 (73F)
New Philadelphia: 73F/2016 (72F)

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.

&&

SYNOPSIS...22
NEAR TERM...Hefferan/22
SHORT TERM...Hefferan
LONG TERM...Hefferan
AVIATION...CL
CLIMATE...McMullen

Hazardous Weather Outlook
National Weather Service Pittsburgh PA
218 PM EDT Wed Jul 26 2023

PAZ074-076-078-WVZ512-514-271830-
Higher Elevations of Westmoreland-Higher Elevations of Fayette-
Higher Elevations of Indiana-Eastern Preston-Eastern Tucker-
218 PM EDT Wed Jul 26 2023

This Hazardous Weather Outlook is for southwest Pennsylvania,
western Pennsylvania and northern West Virginia.

.DAY ONE...This afternoon and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

OHZ039>041-048-057-PAZ007-013-271830-
Tuscarawas-Carroll-Columbiana-Coshocton-Muskingum-Mercer-Lawrence-
218 PM EDT Wed Jul 26 2023

This Hazardous Weather Outlook is for east central Ohio, northwest
Pennsylvania and southwest Pennsylvania.

.DAY ONE...This afternoon and tonight.

There is a Marginal Risk for severe thunderstorms with damaging
winds after 9pm tonight.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Heat index values could exceed 100 degrees on Friday. A Heat
Advisory may be issued.

.SPOTTER INFORMATION STATEMENT...

Weather spotters are encouraged to report significant weather
conditions according to Standard Operating Procedures.

OHZ049-050-058-059-068-069-PAZ008-009-014>016-020>022-029-031-073-
075-077-WVZ001>004-012-021-509>511-513-271830-
Harrison-Jefferson OH-Guernsey-Belmont-Noble-Monroe-Venango-Forest-
Butler-Clarion-Jefferson PA-Beaver-Allegheny-Armstrong-Washington-
Greene-Westmoreland-Fayette-Indiana-Hancock-Brooke-Ohio-Marshall-
Wetzel-Marion-Monongalia-
Ridges of Eastern Monongalia and Northwestern Preston-Preston-
Western Tucker-
218 PM EDT Wed Jul 26 2023

This Hazardous Weather Outlook is for east central Ohio, western
Pennsylvania, and northern West Virginia.

.DAY ONE...This afternoon and tonight.

Hazardous weather is not expected at this time.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Heat index values could exceed 100 degrees on Friday. A Heat
Advisory may be issued in the next 24 hours.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

SKH

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