Alert archive / Iowa / Severe Thunderstorm Watches in 2011
Severe Thunderstorm Watch 295
The Storm Prediction Center issued this severe thunderstorm watch at May 12, 2011, 6:05 PM CDT for 38 counties in Iowa. It took effect at May 12, 2011, 6:10 PM CDT. It was in force for 7 hr.
The area
The outline as issued.
The facts
- Issued
- May 12, 2011, 6:05 PM CDT (23:05 UTC)
- In effect from
- May 12, 2011, 6:10 PM CDT
- Expired
- May 13, 2011, 1:00 AM CDT
- In force
- 7 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 2 in
- Strongest gust expected
- 50 kt
All 38 counties
Adair County, IA, Adams County, IA, Audubon County, IA, Black Hawk County, IA, Boone County, IA, Bremer County, IA, Butler County, IA, Calhoun County, IA, Carroll County, IA, Cass County, IA, Clarke County, IA, Crawford County, IA, Dallas County, IA, Fremont County, IA, Greene County, IA, Grundy County, IA, Guthrie County, IA, Hamilton County, IA, Hardin County, IA, Ida County, IA, Jasper County, IA, Madison County, IA, Mahaska County, IA, Marion County, IA, Marshall County, IA, Mills County, IA, Montgomery County, IA, Page County, IA, Polk County, IA, Pottawattamie County, IA, Poweshiek County, IA, Sac County, IA, Story County, IA, Tama County, IA, Union County, IA, Warren County, IA, Webster County, IA, Woodbury County, IA
The radar
The Des Moines radar (KDMX), 28 km from the middle of the area, began a volume at 23:06 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
- 20%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 20%
- One or more gusts of 65 knots or more
- 5%
- Ten or more severe hail reports
- 60%
- One or more hailstones of 2 inches or more
- 10%
- Six or more combined severe hail and wind reports
- 90%
Warnings issued inside it
8 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 12, 6:28 PM CDT | Severe Thunderstorm Warning | FSD | Cherokee, Ida, Woodbury | 47 min |
| May 12, 7:08 PM CDT | Severe Thunderstorm Warning | DMX | Sac | 37 min |
| May 12, 7:12 PM CDT | Severe Thunderstorm Warning | FSD | Ida, Woodbury | 28 min |
| May 12, 8:01 PM CDT | Severe Thunderstorm Warning | DMX | Crawford | 44 min |
| May 12, 8:21 PM CDT | Severe Thunderstorm Warning | DMX | Carroll, Greene | 39 min |
| May 12, 8:39 PM CDT | Severe Thunderstorm Warning | DMX | Calhoun | 51 min |
| May 12, 9:06 PM CDT | Severe Thunderstorm Warning | DMX | Calhoun, Greene | 39 min |
| May 12, 10:06 PM CDT | Severe Thunderstorm Warning | OAX | Pottawattamie | 39 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
Omaha, NE (KOAX), launched 12:00Z, 11.1 hours before the alert went out and 216 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
- 353 J/kg
- Mixed-layer CIN
- -73 J/kg
- Mixed-layer LCL
- 759 m above ground
- 0-6 km bulk shear
- 21 kt
- 0-1 km storm-relative helicity
- 40 m²/s²
- 0-3 km storm-relative helicity
- 82 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.3
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 11, 8:16 PM CDT | Mesoscale Discussion | SPC | Adams, Fremont, Mills, Montgomery, Page, Taylor | 59 min |
| May 12, 2:37 PM CDT | Tornado Watch | SPC | Harrison, Monona, Shelby | 7 hr |
| May 12, 5:35 PM CDT | Mesoscale Discussion | SPC | Calhoun, Carroll, Crawford, Harrison, Ida, Monona and 4 more | 85 min |
| May 11, 7:51 PM CDT | Mesoscale Discussion | SPC | Dundy, Frontier, Furnas, Hayes, Hitchcock, Red Willow | 84 min |
| May 12, 2:06 PM CDT | Mesoscale Discussion | SPC | Adams, Boone, Buffalo, Butler, Cass, Clay and 39 more | 114 min |
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.