Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1129
The Storm Prediction Center issued this mesoscale discussion at Jun 30, 2021, 11:30 AM EDT for 16 counties in Ohio; 29 counties in Pennsylvania; 9 counties in West Virginia. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Jun 30, 2021, 11:30 AM EDT (15:30 UTC)
- Expired
- Jun 30, 2021, 1:30 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...severe thunderstorm watch likely
- Chance of a watch
- 80%
All 54 counties
Belmont County, OH, Carroll County, OH, Columbiana County, OH, Coshocton County, OH, Guernsey County, OH, Harrison County, OH, Holmes County, OH, Jefferson County, OH, Mahoning County, OH, Monroe County, OH, Morgan County, OH, Muskingum County, OH, Noble County, OH, Stark County, OH, Tuscarawas County, OH, Washington County, OH, Allegheny County, PA, Armstrong County, PA, Beaver County, PA, Blair County, PA, Butler County, PA, Cambria County, PA, Cameron County, PA, Centre County, PA, Clarion County, PA, Clearfield County, PA, Clinton County, PA, Elk County, PA, Fayette County, PA, Forest County, PA, Greene County, PA, Huntingdon County, PA, Indiana County, PA, Jefferson County, PA, Lawrence County, PA, Lycoming County, PA, McKean County, PA, Mercer County, PA, Potter County, PA, Somerset County, PA, Tioga County, PA, Venango County, PA, Warren County, PA, Washington County, PA, Westmoreland County, PA, Brooke County, WV, Hancock County, WV, Marion County, WV, Marshall County, WV, Monongalia County, WV, Ohio County, WV, Pleasants County, WV, Tyler County, WV, Wetzel County, WV
The radar
The Pittsburgh radar (KPBZ), 31 km from the middle of the area, began a volume at 15:32 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, 3.5 hours before the alert went out and 24 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
- 807 J/kg
- Mixed-layer CIN
- -49 J/kg
- Mixed-layer LCL
- 1240 m above ground
- 0-6 km bulk shear
- 32 kt
- 0-1 km storm-relative helicity
- 71 m²/s²
- 0-3 km storm-relative helicity
- 66 m²/s²
- Significant tornado parameter
- 0.1
- Supercell composite
- 1.2
The text
As transmitted.
673
ACUS11 KWNS 301531
SWOMCD
SPC MCD 301530
PAZ000-WVZ000-OHZ000-301730-
Mesoscale Discussion 1129
NWS Storm Prediction Center Norman OK
1030 AM CDT Wed Jun 30 2021
Areas affected...Portions of eastern OH...northern WV...and
western/central PA
Concerning...Severe potential...Severe Thunderstorm Watch likely
Valid 301530Z - 301730Z
Probability of Watch Issuance...80 percent
SUMMARY...Storms capable of producing mainly scattered strong to
damaging winds should develop this afternoon. Severe Thunderstorm
Watch issuance is likely.
DISCUSSION...Stronger mid-level flow associated with an upper trough
over Ontario, Quebec, and the Great Lakes will mostly remain to the
north of PA. Even so, modest enhancement to the mid-level
southwesterlies should overlie parts of the upper OH Valley into
western/central PA this afternoon. Around 25-35 kt of effective bulk
shear is forecast to be present across the warm sector, which should
support some storm organization. Multicell clusters should be the
dominant storm mode given the marginally sufficient deep-layer
shear. Continued diurnal heating of the rather moist low-level
airmass ahead of morning storms in western/central OH will likely
foster 1000-2000 J/kg of MLCAPE by mid afternoon from eastern OH
into northern WV and much of western/central PA. Locally stronger
instability may develop across parts of this region. Steepening
low-level lapse rates should allow for efficient downdraft
accelerations, and scattered damaging wind gusts will likely be the
primary severe threat as storms spread eastward through the
afternoon and early evening. A Severe Thunderstorm Watch will likely
be needed in the next couple of hours as storms gradually increase
in coverage and intensity.
..Gleason/Thompson.. 06/30/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CTP...PBZ...RLX...CLE...
LAT...LON 39538209 39948213 40508212 40988124 41937958 41947831
41927701 41437691 40877724 40227825 39847929 39428045
39318129 39538209SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jun 30, 11:47 AM EDT | Severe Thunderstorm Watch | SPC | Belmont, Carroll, Columbiana, Coshocton, Guernsey, Harrison and 5 more | 7 hr |
| Jun 30, 12:46 PM EDT | Severe Thunderstorm Watch | SPC | Ashtabula, Geauga, Mahoning, Portage, Stark, Trumbull | 7 hr |
| Jun 30, 2:16 PM EDT | Mesoscale Discussion | SPC | Carbon, Lackawanna, Luzerne, Monroe, Pike, Wayne and 1 more | 119 min |
| Jun 30, 3:21 PM EDT | Severe Thunderstorm Watch | SPC | Berks, Bradford, Carbon, Lackawanna, Lehigh, Luzerne and 6 more | 7 hr |
| Jun 30, 3:29 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Bedford, Blair, Cambria, Centre and 16 more | 2 hr |
| Jun 30, 4:41 PM EDT | Mesoscale Discussion | SPC | Adams, Bedford, Berks, Blair, Columbia, Cumberland and 17 more | 2 hr |
| Jun 30, 4:48 PM EDT | Mesoscale Discussion | SPC | Lackawanna, Susquehanna, Wayne | 87 min |
| Jun 30, 4:51 PM EDT | Severe Thunderstorm Watch | SPC | Adams, Cumberland, Dauphin, Franklin, Lancaster, Lebanon and 3 more | 3 hr |
| Jun 30, 6:58 PM EDT | Mesoscale Discussion | SPC | Adams, Berks, Lancaster, Lebanon, Lehigh, Northampton and 1 more | 92 min |
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.