Tornado and Flash Flooding in Pennsylvania, August 6, 2024

Area Forecast Discussion
National Weather Service Pittsburgh PA
1049 AM EDT Tue Aug 6 2024

.SYNOPSIS...
Showers and thunderstorms are expected today, mainly this
afternoon and evening, as low pressure crosses the region. Some
storms could be severe with damaging wind and large hail. Shower
chances will continue into Wednesday as the low exits. Periodic
shower chances continue east of Pittsburgh until a cold front
brings chances for area wide showers and thunderstorms Friday.

&&

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

- Showers and thunderstorms likely mainly this afternoon and
  evening
- Severe storms possible with damaging wind, large hail, and
  isolated tornadoes

_______________________________________________________________

Initial storms are already firing in northeast Ohio/far
northwest PA, with lift aided by the right entrance region of a
jet over southern Quebec. These cells will be moving into a
region, north of I-80, that may already have 1000-1500 J/kg of
MLCAPE by noon, along with 35-40 knots of effective shear. This
environment allow the storms to continue to organize and grow
upscale, possibly bringing a first round of strong to severe
storms north of Pittsburgh before a second round develops during
the mid to late afternoon hours. Damaging wind would be the
most likely threat with this initial round, but as surface
vorticity/0-3km CAPE continues to increase, a tornado threat
cannot be ruled out as well.

A more widespread severe threat is still forecast to evolve
during the mid-afternoon hours, as the main shortwave trough
over the Great Lakes approaches and interacts with the quasi-
stationary boundary over eastern Ohio and western PA. MLCAPE may
increase to the 1500-2000 J/kg range by then, with a stronger,
more elongated shear profile developing as well with better
hodograph curvature. While damaging wind will be the more
widespread severe threat once activity organizes, supercell
structures will be possible given the environment, raising the
potential for isolated instances of large hail and tornadoes.
The most concerning corridor would likely be between Pittsburgh
and I-80. CAMs timing differences still exist, and will hope for
more clarity once more 12Z data comes in.

Instability will gradually wane through the evening, with a
diminishing severe weather potential. Scattered showers and an
isolated thunderstorm are still expected overnight as the
shortwave crosses the region.

Hot and humid weather today will produce heat indices in the
mid 90s across SE OH and the lower terrain areas of WV. Lows
tonight will drop close to seasonable levels.

&&

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

- Shower chances decrease on Wednesday
- Dry for most locations through Thursday night, though low
  shower chances continue east of Pittsburgh

__________________________________________________________

Shower and thunderstorm chances will taper off from W-E
Wednesday as the shortwave exits the region. Much of the area
will then be dry through Thursday night as high pressure builds
to the north of the area.

A tropical low is expected to be near the SE Coast mid to late
week. Moisture rotating around the low, and easterly flow, will
keep shower chances in the forecast for areas mainly east of
Pittsburgh for Thursday and Thursday night. Temperatures should
be closer to seasonable levels through the period.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
KEY MESSAGES:

- Unsettled to start, with dry weather later in the period
- Cooler temperatures, especially over the weekend

_____________________________________________________________

Model ensembles indicate the remnant tropical low should move
north late in the week, as a northern stream shortwave trough
tracks across the Great Lakes and Upper Ohio Valley region.
These systems should phase late Friday/Saturday, and move off
the East Coast. Shower and thunderstorm chances increase on
Friday as the northern stream trough crosses the region. The
greatest uncertainty in the forecast is how quickly phasing
occurs, and this will affect POPs and rainfall amounts across
the Upper Ohio Valley region. Stayed close to the NBM (National
Blend) with this uncertainty.

Rain chances should diminish Saturday as the initial systems
exit. Another shortwave rotating around an upper low across
eastern Canada should bring low chances for showers north of I
80 on Sunday, with dry weather returning Monday under high
pressure.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
IFR/LIFR fog and stratus is expected at FKL and DUJ through
early morning with low level moisture in place due to showers
and thunderstorms Monday evening. Expect a gradual improvement
back to VFR cigs by late morning/early afternoon as mixing
increases. Elsewhere, VFR is expected through much of the day
ahead of an approaching shortwave trough and surface low
pressure. Model soundings indicate a scattered-broken cumulus
layer will develop, with increasing mid clouds above.

Thunderstorms are expected to develop ahead of the approaching
shortwave, as surface low pressure tracks east along a stalled
surface front. The greatest uncertainty exists in the timing of
these storms. Included TEMPO groups for all ports for the most
likely time of occurrence. In general, expect a broken line of
storms to sweep across NW PA first, tracking ESE across the
remainder of the region through the late afternoon and evening.
For PIT, included a time range from 22Z through 02Z for thunder.
Severe storms are possible.

Expect mainly VFR just behind the line of storms this evening,
with deterioration to MVFR, and IFR, as stratus develops with
low level moisture Tuesday night.

.Outlook...
IFR stratus is likely Wednesday morning, with improvement to VFR
by afternoon. Restrictions are possible again by Friday as
moisture streams north along a crossing cold front. VFR should
return Saturday as high pressure builds in.

&&

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

&&

SYNOPSIS...WM
NEAR TERM...WM/CL
SHORT TERM...WM
LONG TERM...WM
AVIATION...WM

Hazardous Weather Outlook
National Weather Service Pittsburgh PA
358 AM EDT Tue Aug 6 2024

OHZ039>041-048>050-057>059-PAZ007>009-013>016-020>022-029-031-
073>078-WVZ001>004-070800-
Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson OH-
Muskingum-Guernsey-Belmont-Mercer-Venango-Forest-Lawrence-Butler-
Clarion-Jefferson PA-Beaver-Allegheny-Armstrong-Washington-Greene-
Westmoreland-Higher Elevations of Westmoreland-Fayette-
Higher Elevations of Fayette-Indiana-Higher Elevations of Indiana-
Hancock-Brooke-Ohio-Marshall-
358 AM EDT Tue Aug 6 2024

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

.DAY ONE...Today and tonight.

There is a Slight Risk (or level 2 out of 5) for severe thunderstorms
this afternoon and evening. The main hazard is expected to be
damaging wind, though isolated tornadoes and large hail are also
possible. In addition, locally heavy rainfall could result in
localized flooding, especially for areas that see multiple
thunderstorms.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

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

OHZ068-069-WVZ012-021-509>514-070800-
Noble-Monroe-Wetzel-Marion-Monongalia-
Ridges of Eastern Monongalia and Northwestern Preston-Preston-
Eastern Preston-Western Tucker-Eastern Tucker-
358 AM EDT Tue Aug 6 2024

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

.DAY ONE...Today and tonight.

There is a Marginal Risk (or level 1 out of 5) for severe
thunderstorms this afternoon and evening. The main hazard is expected
to be damaging wind.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

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

WM

Special Weather Statement
National Weather Service Pittsburgh PA
1110 AM EDT Tue Aug 6 2024

PAZ007-008-061600-
Venango PA-Mercer PA-
1110 AM EDT Tue Aug 6 2024

...STRONG THUNDERSTORMS WILL IMPACT NORTHEASTERN MERCER AND NORTHERN
VENANGO COUNTIES THROUGH NOON EDT...

At 1110 AM EDT, Doppler radar was tracking strong thunderstorms along
a line extending from 6 miles northwest of Titusville to near Guys
Mills to 7 miles east of Atlantic. Movement was east at 30 mph.

HAZARD...Wind gusts up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Sugarcreek, Rouseville, Cooperstown, Pleasantville, Oil Creek State
Park, and Maurice K Goddard State Park.

This includes Interstate 79 in Pennsylvania near mile marker 137.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4162 7951 4158 7951 4153 7953 4144 7978
      4147 8024 4148 8021 4149 8000 4151 7998
      4151 7996 4154 7994 4154 7992 4156 7991
      4160 7983 4162 7983
TIME...MOT...LOC 1510Z 275DEG 25KT 4167 7979 4157 7995 4148 8020

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

MLB