Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1477
The Storm Prediction Center issued this mesoscale discussion at Aug 11, 2021, 11:50 AM EDT for 6 counties in Ohio; 18 counties in Pennsylvania; Brooke County, Hancock County, Ohio County, West Virginia. It was in force for 115 min.
The area
The outline as issued.
The facts
- Issued
- Aug 11, 2021, 11:50 AM EDT (15:50 UTC)
- Expired
- Aug 11, 2021, 1:45 PM EDT
- In force
- 115 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 27 counties
Carroll County, OH, Columbiana County, OH, Harrison County, OH, Jefferson County, OH, Mahoning County, OH, Trumbull County, OH, Allegheny County, PA, Armstrong County, PA, Beaver County, PA, Butler County, PA, Cambria County, PA, Clarion County, PA, Clearfield County, PA, Elk County, PA, Fayette County, PA, Forest County, PA, Indiana County, PA, Jefferson County, PA, Lawrence County, PA, Mercer County, PA, Somerset County, PA, Venango County, PA, Washington County, PA, Westmoreland County, PA, Brooke County, WV, Hancock County, WV, Ohio County, WV
The radar
The Pittsburgh radar (KPBZ), 26 km from the middle of the area, began a volume at 15:51 UTC, the scan nearest the moment this went out.
Open the radar archive at this moment
The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.
The watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Pittsburgh, PA (KPIT), launched 12:00Z, 3.8 hours before the alert went out and 27 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.
- Mixed-layer CAPE
- 267 J/kg
- Mixed-layer CIN
- -243 J/kg
- Mixed-layer LCL
- 1321 m above ground
- 0-6 km bulk shear
- 18 kt
- 0-1 km storm-relative helicity
- 131 m²/s²
- 0-3 km storm-relative helicity
- 188 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
090
ACUS11 KWNS 111550
SWOMCD
SPC MCD 111550
PAZ000-WVZ000-OHZ000-111745-
Mesoscale Discussion 1477
NWS Storm Prediction Center Norman OK
1050 AM CDT Wed Aug 11 2021
Areas affected...Portions of far eastern OH...the extreme northern
WV Panhandle...and western/central PA
Concerning...Severe potential...Watch possible
Valid 111550Z - 111745Z
Probability of Watch Issuance...40 percent
SUMMARY...At least an isolated damaging wind threat may continue
with storms through the early afternoon. Watch issuance is possible.
DISCUSSION...A small cluster of storms with a history of producing
near-severe wind gusts is presently moving eastward across far
eastern OH late this morning. Although some weak convective
inhibition remains in the boundary layer per recent mesoanalysis
estimates, continued diurnal heating should erode this inhibition
within the next couple of hours. A rather moist low-level airmass is
present downstream of the ongoing convection, with with surface
dewpoints generally in the low to mid 70s. Although the low-level
winds across western PA are not overly strong per KPBZ VWPs, there
is some increase to around 30-35 kt of westerly flow around 6 km
AGL. This may be enough to support continued modest storm
organization. Steepening low-level lapses promoting efficient
downward momentum transfer and a linear mode both suggest that at
least isolated damaging wind gusts should be the main threat with
this activity through the early afternoon. Depending on convective
intensity trends over the next hour or two, Severe Thunderstorm
Watch issuance is possible.
..Gleason/Thompson.. 08/11/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CTP...PBZ...CLE...
LAT...LON 40468143 40758088 41588079 41597871 41317812 40307843
39827891 39777962 40158096 40468143SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 10, 8:12 PM EDT | Mesoscale Discussion | SPC | Williams | 63 min |
| Aug 10, 8:38 PM EDT | Severe Thunderstorm Watch | SPC | Williams | 5 hr |
| Aug 10, 10:57 PM EDT | Mesoscale Discussion | SPC | Defiance, Fulton, Henry, Lucas, Paulding, Putnam and 2 more | 93 min |
| Aug 11, 9:31 AM EDT | Mesoscale Discussion | SPC | Ashland, Ashtabula, Carroll, Columbiana, Coshocton, Crawford and 19 more | 89 min |
| Aug 11, 10:52 AM EDT | Mesoscale Discussion | SPC | Defiance, Paulding, Williams | 83 min |
| Aug 11, 11:50 AM EDT | Severe Thunderstorm Watch | SPC | Allen, Defiance, Fulton, Henry, Paulding, Putnam and 2 more | 4 hr |
| Aug 11, 1:26 PM EDT | Mesoscale Discussion | SPC | Allen, Defiance, Fulton, Henry, Paulding, Putnam and 2 more | 94 min |
| Aug 11, 2:12 PM EDT | Mesoscale Discussion | SPC | Allen, Ashland, Auglaize, Champaign, Crawford, Delaware and 26 more | 93 min |
| Aug 11, 2:32 PM EDT | Severe Thunderstorm Watch | SPC | Ashland, Auglaize, Champaign, Clark, Crawford, Cuyahoga and 28 more | 4 hr |
| Aug 11, 4:24 PM EDT | Mesoscale Discussion | SPC | Athens, Belmont, Carroll, Clinton, Columbiana, Coshocton and 31 more | 96 min |
| Aug 11, 4:57 PM EDT | Severe Thunderstorm Watch | SPC | Ashtabula, Belmont, Carroll, Columbiana, Coshocton, Geauga and 13 more | 3 hr |
| Aug 11, 2:03 PM EDT | Mesoscale Discussion | SPC | Adams, Armstrong, Bedford, Berks, Blair, Bucks and 42 more | 87 min |
| Aug 11, 3:02 PM EDT | Severe Thunderstorm Watch | SPC | Adams, Bedford, Berks, Blair, Bucks, Carbon and 26 more | 6 hr |
| Aug 11, 6:44 PM EDT | Mesoscale Discussion | SPC | Berks, Bucks, Carbon, Chester, Delaware, Lancaster and 6 more | 91 min |
| Aug 11, 1:01 PM EDT | Mesoscale Discussion | SPC | Berkeley, Grant, Hampshire, Hardy, Jefferson, Mineral and 3 more | 89 min |
| Aug 11, 2:02 PM EDT | Severe Thunderstorm Watch | SPC | Berkeley, Hampshire, Hardy, Jefferson, Mineral, Morgan | 6 hr |
Nearby
Mesoscale Discussions in Pennsylvania, 2021Mesoscale Discussions in Ohio, 2021Mesoscale Discussions in West Virginia, 2021Every mesoscale discussion in 2021
Sources
The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.