Alert archive / Ohio / Mesoscale Discussions in 2021
Mesoscale Discussion 1499
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 3:17 PM EDT for 19 counties in Ohio; 7 counties in Pennsylvania; Brooke County, Hancock County, Ohio County, West Virginia. It was in force for 58 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 3:17 PM EDT (19:17 UTC)
- Expired
- Aug 12, 2021, 4:15 PM EDT
- In force
- 58 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...severe thunderstorm watch likely
- Chance of a watch
- 80%
All 29 counties
Ashland County, OH, Carroll County, OH, Columbiana County, OH, Coshocton County, OH, Cuyahoga County, OH, Geauga County, OH, Guernsey County, OH, Harrison County, OH, Holmes County, OH, Jefferson County, OH, Lorain County, OH, Mahoning County, OH, Medina County, OH, Portage County, OH, Stark County, OH, Summit County, OH, Trumbull County, OH, Tuscarawas County, OH, Wayne County, OH, Allegheny County, PA, Beaver County, PA, Butler County, PA, Crawford County, PA, Lawrence County, PA, Mercer County, PA, Washington County, PA, Brooke County, WV, Hancock County, WV, Ohio County, WV
The radar
The Cleveland radar (KCLE), 87 km from the middle of the area, began a volume at 19:16 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, 7.3 hours before the alert went out and 105 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.
944
ACUS11 KWNS 121917
SWOMCD
SPC MCD 121917
PAZ000-WVZ000-OHZ000-122015-
Mesoscale Discussion 1499
NWS Storm Prediction Center Norman OK
0217 PM CDT Thu Aug 12 2021
Areas affected...northeast and east-central OH...WV
Panhandle...western PA
Concerning...Severe potential...Severe Thunderstorm Watch likely
Valid 121917Z - 122015Z
Probability of Watch Issuance...80 percent
SUMMARY...Convective initiation is being monitored for over
northeast OH during the through 4pm. If/once storms develop and
subsequently intensify, the environment over adjacent parts of
OH/WV/PA supports the stronger storms being capable of 55-65 mph
gusts and wind damage.
DISCUSSION...Visible satellite imagery shows a swelling cumulus
field with the initial signs of glaciation occurring southwest of
Cleveland as of 305pm. A series of gravity waves are implied in the
cumulus field, but this seems to have little overall impact for
convective initiation. More consequential, an MCV located over the
northwest quadrant of OH will continue to move east towards
northeast OH. Ascent associated with this feature appears to be
having some influence in the onset of more appreciable convective
development. With upper 80s surface temperatures and middle 70s
dewpoints, the 17z run of the RAP appears to have an accurate
depiction of the surface conditions. The RAP forecast soundings
show around 3000 J/kg MLCAPE over northeast OH. The 30-40 kt flow
in the 700-500 mb layer (per the RAP soundings) will aid in some
multicellular organization once convective initiation occurs. The
primary risks with the stronger storms will be gusts in the 55-65
mph range and perhaps marginally severe hail. The area from
northeast OH into western PA is being considered for a severe
thunderstorm watch.
..Smith/Thompson.. 08/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PBZ...CLE...ILN...
LAT...LON 40448242 41418233 42028032 41047959 40127967 40018197
40448242SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 12, 3:48 PM EDT | Severe Thunderstorm Watch | SPC | Ashtabula, Carroll, Columbiana, Cuyahoga, Geauga, Harrison and 12 more | 6 hr |
| Aug 12, 6:22 PM EDT | Mesoscale Discussion | SPC | Belmont, Carroll, Columbiana, Harrison, Jefferson, Mahoning | 83 min |
| 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 Ohio, 2021Mesoscale Discussions in Pennsylvania, 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.