Alert archive / Iowa / Severe Thunderstorm Watches in 2011
Severe Thunderstorm Watch 824
The Storm Prediction Center issued this severe thunderstorm watch at Sep 2, 2011, 10:23 PM CDT for 32 counties in Iowa. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Sep 2, 2011, 10:23 PM CDT (03:23 UTC)
- Expired
- Sep 3, 2011, 4:00 AM CDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1 in
- Strongest gust expected
- 60 kt
All 32 counties
Adair County, IA, Benton County, IA, Black Hawk County, IA, Boone County, IA, Buchanan County, IA, Cass County, IA, Cedar County, IA, Clinton County, IA, Dallas County, IA, Delaware County, IA, Dubuque County, IA, Greene County, IA, Grundy County, IA, Guthrie County, IA, Hardin County, IA, Iowa County, IA, Jackson County, IA, Jasper County, IA, Johnson County, IA, Jones County, IA, Keokuk County, IA, Linn County, IA, Madison County, IA, Mahaska County, IA, Marion County, IA, Marshall County, IA, Polk County, IA, Poweshiek County, IA, Story County, IA, Tama County, IA, Warren County, IA, Washington County, IA
The radar
The Des Moines radar (KDMX), 37 km from the middle of the area, began a volume at 03:23 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.
What SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 10%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 30%
- One or more gusts of 65 knots or more
- 20%
- Ten or more severe hail reports
- 10%
- One or more hailstones of 2 inches or more
- 5%
- Six or more combined severe hail and wind reports
- 60%
Warnings issued inside it
5 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 2, 10:48 PM CDT | Severe Thunderstorm Warning | DMX | Boone, Dallas, Greene, Guthrie | 42 min |
| Sep 2, 11:02 PM CDT | Severe Thunderstorm Warning | DMX | Black Hawk, Bremer, Butler, Grundy, Marshall, Tama | 46 min |
| Sep 2, 11:25 PM CDT | Severe Thunderstorm Warning | DMX | Boone, Dallas, Polk, Story | 34 min |
| Sep 2, 11:45 PM CDT | Severe Thunderstorm Warning | DMX | Black Hawk, Bremer | 45 min |
| Sep 2, 11:50 PM CDT | Severe Thunderstorm Warning | DVN | Buchanan, Delaware | 55 min |
Discussions around it
SPC mesoscale discussions over the same counties from four hours before the watch to its end.
The nearest sounding before it
Davenport, (KDVN), launched 00:00Z, 3.4 hours before the alert went out and 238 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
- 1861 J/kg
- Mixed-layer CIN
- -107 J/kg
- Mixed-layer LCL
- 1596 m above ground
- 0-6 km bulk shear
- 29 kt
- 0-1 km storm-relative helicity
- 87 m²/s²
- 0-3 km storm-relative helicity
- 165 m²/s²
- Significant tornado parameter
- 0.2
- Supercell composite
- 3.6
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 2, 10:04 PM CDT | Mesoscale Discussion | SPC | Adair, Adams, Audubon, Benton, Black Hawk, Boone and 22 more | 86 min |
| Sep 2, 11:56 PM CDT | Mesoscale Discussion | SPC | Benton, Black Hawk, Boone, Buchanan, Cedar, Clayton and 26 more | 94 min |
| Sep 3, 12:48 AM CDT | Severe Thunderstorm Watch | SPC | Clayton, Fayette | 6 hr |
Nearby
Severe Thunderstorm Watches in Iowa, 2011Every severe thunderstorm watch in 2011
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.