Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1134
The Storm Prediction Center issued this mesoscale discussion at Jun 30, 2021, 3:29 PM EDT for 22 counties in Pennsylvania. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Jun 30, 2021, 3:29 PM EDT (19:29 UTC)
- Expired
- Jun 30, 2021, 5:30 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 328
All 22 counties
Allegheny County, PA, Armstrong County, PA, Bedford County, PA, Blair County, PA, Cambria County, PA, Centre County, PA, Clearfield County, PA, Clinton County, PA, Fayette County, PA, Greene County, PA, Huntingdon County, PA, Indiana County, PA, Juniata County, PA, Lycoming County, PA, Mifflin County, PA, Montour County, PA, Northumberland County, PA, Snyder County, PA, Somerset County, PA, Union County, PA, Washington County, PA, Westmoreland County, PA
The radar
The State College radar (KCCX), 85 km from the middle of the area, began a volume at 19:29 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, 7.5 hours before the alert went out and 108 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.
357
ACUS11 KWNS 301929
SWOMCD
SPC MCD 301929
PAZ000-MDZ000-WVZ000-302130-
Mesoscale Discussion 1134
NWS Storm Prediction Center Norman OK
0229 PM CDT Wed Jun 30 2021
Areas affected...Central to western Pennsylvania
Concerning...Severe Thunderstorm Watch 328...
Valid 301929Z - 302130Z
The severe weather threat for Severe Thunderstorm Watch 328
continues.
SUMMARY...The threat for damaging wind continues for southwest to
central Pennsylvania as thunderstorm coverage gradually increases.
DISCUSSION...Regional radar imagery shows a gradual increase in
thunderstorm coverage across far eastern OH and central PA along a
diffuse surface trough. Most storms in this region have shown a
tendency for outrunning outflows and/or becoming driven by cold-pool
propagation, but a few have shown sufficient
organization/intensification for damaging winds. Temperatures
warming into the low 90s are sustaining 1500-2000 J/kg MLCAPE over
the region as well as 8-9 C/km low-level lapse rates. These
thermodynamics combined with 30-40 knots of effective bulk shear
will maintain a conditionally favorable damaging wind environment
that may be realized by any stronger downburst or clusters that can
develop organized outflows oriented orthogonal to the westerly mean
flow. The damaging wind threat will likely be highest from southwest
to central PA for the next 1-2 hours where more robust convection is
noted in IR imagery and echo top data. The severe risk should
gradually shift to the east/northeast of ongoing convection through
late afternoon.
..Moore.. 06/30/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CTP...LWX...PBZ...
LAT...LON 40428044 40697981 41187876 41537783 41707720 41367660
40907656 40557694 40257762 39827832 39647922 39647992
39648039 39768058 40078050 40428044SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jun 30, 11:30 AM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Blair, Butler, Cambria and 23 more | 2 hr |
| Jun 30, 11:47 AM EDT | Severe Thunderstorm Watch | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Fayette and 9 more | 7 hr |
| Jun 30, 12:46 PM EDT | Severe Thunderstorm Watch | SPC | Bedford, Blair, Cambria, Cameron, Centre, Clearfield and 20 more | 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, 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, 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.