Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1503
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 6:22 PM EDT for 6 counties in Ohio; 27 counties in Pennsylvania; Brooke County, Hancock County, Ohio County, West Virginia. It was in force for 83 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 6:22 PM EDT (22:22 UTC)
- Expired
- Aug 12, 2021, 7:45 PM EDT
- In force
- 83 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 431...433
All 36 counties
Belmont County, OH, Carroll County, OH, Columbiana County, OH, Harrison County, OH, Jefferson County, OH, Mahoning 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, Crawford County, PA, Elk County, PA, Forest County, PA, Indiana County, PA, Jefferson County, PA, Lawrence County, PA, Lycoming County, PA, McKean County, PA, Mercer County, PA, Mifflin County, PA, Potter County, PA, Union County, PA, Venango County, PA, Warren County, PA, Washington County, PA, Westmoreland County, PA, Brooke County, WV, Hancock County, WV, Ohio County, WV
The radar
The State College radar (KCCX), 95 km from the middle of the area, began a volume at 22:22 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 nearest sounding before it
Pittsburgh, PA (KPIT), launched 12:00Z, 10.4 hours before the alert went out and 96 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
- 1075 J/kg
- Mixed-layer CIN
- -107 J/kg
- Mixed-layer LCL
- 890 m above ground
- 0-6 km bulk shear
- 21 kt
- 0-1 km storm-relative helicity
- 163 m²/s²
- 0-3 km storm-relative helicity
- 129 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 1.8
The text
As transmitted.
871
ACUS11 KWNS 122223
SWOMCD
SPC MCD 122222
PAZ000-WVZ000-OHZ000-122345-
Mesoscale Discussion 1503
NWS Storm Prediction Center Norman OK
0522 PM CDT Thu Aug 12 2021
Areas affected...Far eastern Ohio and west-central Pennsylvania
Concerning...Severe Thunderstorm Watch 431...433...
Valid 122222Z - 122345Z
The severe weather threat for Severe Thunderstorm Watch 431, 433
continues.
SUMMARY...A cluster of strong to severe thunderstorms will continue
to pose a risk for damaging wind gusts through early evening.
DISCUSSION...As of 2200 UTC, regional radar and satellite imagery
showed a cluster of strong to severe thunderstorms across eastern
Ohio and western Pennsylvania. Ongoing along a weak stationary
frontal zone and outflow from previous convection, a very buoyant
airmass remains in place ahead of the cluster. 3000-3500 J/kg of
MLCAPE but weak vertical shear will support robust multicell
updrafts into early evening. Model soundings show steep low-level
lapse rates and favoring strong downdrafts. As additional storm
development reinforces the surface cold pool, a few severe gusts
will remain possible this evening across WW433 and western portions
of WW431. Storm should eventually begin to weaken across central PA
with the loss of diurnal heating later this evening, reducing the
risk for damaging wind gusts.
..Lyons.. 08/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CTP...PBZ...CLE...
LAT...LON 40317890 40007974 39888047 39908121 40318149 40748116
41228088 41648033 41927941 41937816 41837738 41667709
41237697 40767708 40567760 40467846 40317890SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 12, 3:17 PM EDT | Mesoscale Discussion | SPC | Ashland, Carroll, Columbiana, Coshocton, Cuyahoga, Geauga and 13 more | 58 min |
| Aug 12, 3:48 PM EDT | Severe Thunderstorm Watch | SPC | Ashtabula, Carroll, Columbiana, Cuyahoga, Geauga, Harrison and 12 more | 6 hr |
| Aug 12, 11:03 AM EDT | Mesoscale Discussion | SPC | Susquehanna | 2 hr |
| Aug 12, 12:19 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Blair, Butler, Cambria, Cameron and 20 more | 116 min |
| Aug 12, 1:11 PM EDT | Severe Thunderstorm Watch | SPC | Armstrong, Bedford, Blair, Cambria, Cameron, Centre and 27 more | 9 hr |
| Aug 12, 1:42 PM EDT | Severe Thunderstorm Watch | SPC | Bradford, Lackawanna, Luzerne, Pike, Susquehanna, Wayne and 1 more | 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.