Alert archive / Iowa / Mesoscale Discussions in 2021
Mesoscale Discussion 1461
The Storm Prediction Center issued this mesoscale discussion at Aug 10, 2021, 1:12 PM CDT for 41 counties in Iowa. It was in force for 93 min.
The area
The outline as issued.
The facts
- Issued
- Aug 10, 2021, 1:12 PM CDT (18:12 UTC)
- Expired
- Aug 10, 2021, 2:45 PM CDT
- In force
- 93 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 41 counties
Appanoose County, IA, Benton County, IA, Black Hawk County, IA, Bremer County, IA, Buchanan County, IA, Butler County, IA, Cedar County, IA, Clarke County, IA, Clayton County, IA, Davis County, IA, Decatur County, IA, Delaware County, IA, Dubuque County, IA, Fayette County, IA, Grundy County, IA, Hardin County, IA, Henry County, IA, Iowa County, IA, Jasper County, IA, Jefferson County, IA, Johnson County, IA, Jones County, IA, Keokuk County, IA, Linn County, IA, Lucas County, IA, Madison County, IA, Mahaska County, IA, Marion County, IA, Marshall County, IA, Monroe County, IA, Polk County, IA, Poweshiek County, IA, Ringgold County, IA, Story County, IA, Tama County, IA, Union County, IA, Van Buren County, IA, Wapello County, IA, Warren County, IA, Washington County, IA, Wayne County, IA
The radar
The Des Moines radar (KDMX), 98 km from the middle of the area, began a volume at 18:15 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
Davenport, (KDVN), launched 12:00Z, 6.2 hours before the alert went out and 170 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
- 3755 J/kg
- Mixed-layer CIN
- -67 J/kg
- Mixed-layer LCL
- 819 m above ground
- 0-6 km bulk shear
- 12 kt
- 0-1 km storm-relative helicity
- -37 m²/s²
- 0-3 km storm-relative helicity
- 4 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
640
ACUS11 KWNS 101812
SWOMCD
SPC MCD 101812
WIZ000-IAZ000-101945-
Mesoscale Discussion 1461
NWS Storm Prediction Center Norman OK
0112 PM CDT Tue Aug 10 2021
Areas affected...Portions of south-central and eastern Iowa
Concerning...Severe potential...Watch possible
Valid 101812Z - 101945Z
Probability of Watch Issuance...40 percent
SUMMARY...Monitoring storm intensity/coverage across eastern Iowa
for a potential severe thunderstorm watch.
DISCUSSION...A storm has formed in Clarke County, Iowa. SPC
mesoanalysis and forecast soundings would suggest a bit more warming
would have been expected before widespread surface based storm
development was imminent. However, radar characteristics suggest
this storm could be surface based. Therefore, more widespread
surface based storm development may be more imminent than previously
thought. Instability across eastern Iowa is extreme with MLCAPE
around 4000 J/kg and mid-level lapse rates around 8 C/km per SPC
mesoanalysis.
Based on the DMX and EAX VWPs there appears to be some stronger
mid-level flow across southern Iowa which may provide enough shear
for some better storm organization.
Therefore, given the extreme instability and at least modest shear,
any sustained, organized convection will likely be severe. The
primary question at this time will be storm coverage. Therefore,
storm trends will continue to be monitored and if/when stronger,
sustained updrafts appear imminent, a watch may become necessary.
..Bentley/Thompson.. 08/10/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...DVN...ARX...DMX...
LAT...LON 40689447 41899378 42999273 42919114 42509083 41339121
40709169 40689447SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 10, 2:08 PM CDT | Severe Thunderstorm Watch | SPC | Allamakee, Benton, Black Hawk, Bremer, Buchanan, Cedar and 28 more | 6 hr |
| Aug 10, 5:51 PM CDT | Mesoscale Discussion | SPC | Cedar, Clinton, Jackson, Jones, Muscatine, Scott | 84 min |
Nearby
Mesoscale Discussions in Iowa, 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.