Alert archive / Iowa / Tornado Watches in 2011
Tornado Watch 282
The Storm Prediction Center issued this tornado watch at May 11, 2011, 2:53 PM CDT for 39 counties in Iowa; 30 counties in Nebraska. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- May 11, 2011, 2:53 PM CDT (19:53 UTC)
- Expired
- May 11, 2011, 9:00 PM CDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 2 in
- Strongest gust expected
- 60 kt
All 69 counties
Adair County, IA, Adams County, IA, Appanoose County, IA, Audubon County, IA, Boone County, IA, Carroll County, IA, Cass County, IA, Clarke County, IA, Crawford County, IA, Dallas County, IA, Davis County, IA, Decatur County, IA, Fremont County, IA, Greene County, IA, Guthrie County, IA, Harrison County, IA, Jasper County, IA, Lucas County, IA, Madison County, IA, Mahaska County, IA, Marion County, IA, Marshall County, IA, Mills County, IA, Monona County, IA, Monroe County, IA, Montgomery County, IA, Page County, IA, Polk County, IA, Pottawattamie County, IA, Poweshiek County, IA, Ringgold County, IA, Shelby County, IA, Story County, IA, Tama County, IA, Taylor County, IA, Union County, IA, Wapello County, IA, Warren County, IA, Wayne County, IA, Antelope County, NE, Boone County, NE, Burt County, NE, Butler County, NE, Cass County, NE, Colfax County, NE, Cuming County, NE, Dodge County, NE, Douglas County, NE, Greeley County, NE, Hall County, NE, Hamilton County, NE, Howard County, NE, Lancaster County, NE, Madison County, NE, Merrick County, NE, Nance County, NE, Otoe County, NE, Pierce County, NE, Platte County, NE, Polk County, NE, Sarpy County, NE, Saunders County, NE, Seward County, NE, Stanton County, NE, Thurston County, NE, Washington County, NE, Wayne County, NE, Wheeler County, NE, York County, NE
The radar
The Omaha radar (KOAX), 30 km from the middle of the area, began a volume at 19:56 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
- 40%
- One or more EF2 to EF5 tornadoes
- 20%
- Ten or more severe wind reports
- 30%
- One or more gusts of 65 knots or more
- 30%
- Ten or more severe hail reports
- 40%
- One or more hailstones of 2 inches or more
- 30%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
30 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 11, 2:56 PM CDT | Severe Thunderstorm Warning | OAX | Mills, Pottawattamie | 49 min |
| May 11, 2:58 PM CDT | Severe Thunderstorm Warning | GID | Hamilton, York | 32 min |
| May 11, 3:03 PM CDT | Tornado Warning | GID | Hamilton, Merrick, Nance, Polk | 27 min |
| May 11, 3:14 PM CDT | Tornado Warning | GID | Polk | 12 min |
| May 11, 3:18 PM CDT | Severe Thunderstorm Warning | OAX | Platte | 42 min |
| May 11, 3:23 PM CDT | Severe Thunderstorm Warning | GID | Hamilton, Merrick, Nance, Polk | 40 min |
| May 11, 3:26 PM CDT | Severe Thunderstorm Warning | OAX | Burt, Butler, Colfax, Cuming, Dodge, Douglas and 4 more | 49 min |
| May 11, 3:28 PM CDT | Tornado Warning | GID | Merrick, Nance | 15 min |
| May 11, 3:52 PM CDT | Severe Thunderstorm Warning | OAX | Antelope, Boone, Madison, Platte, Stanton | 38 min |
| May 11, 3:56 PM CDT | Severe Thunderstorm Warning | OAX | Burt, Colfax, Cuming, Dodge, Stanton, Thurston and 1 more | 49 min |
| May 11, 3:57 PM CDT | Severe Thunderstorm Warning | OAX | Monona | 48 min |
| May 11, 4:01 PM CDT | Severe Thunderstorm Warning | DMX | Adams, Taylor | 44 min |
| May 11, 4:11 PM CDT | Tornado Warning | DMX | Adams, Taylor | 49 min |
| May 11, 4:28 PM CDT | Severe Thunderstorm Warning | OAX | Antelope, Madison, Pierce, Stanton, Wayne | 32 min |
| May 11, 4:31 PM CDT | Severe Thunderstorm Warning | OAX | Burt, Cuming, Stanton, Thurston, Wayne | 29 min |
| May 11, 4:34 PM CDT | Flash Flood Warning | OAX | Montgomery, Page | 67 min |
| May 11, 4:42 PM CDT | Flash Flood Warning | DMX | Adams, Taylor | 6 hr |
| May 11, 4:50 PM CDT | Tornado Warning | DMX | Adams, Union | 40 min |
| May 11, 4:57 PM CDT | Severe Thunderstorm Warning | DMX | Adams, Taylor | 38 min |
| May 11, 5:32 PM CDT | Severe Thunderstorm Warning | DMX | Adams, Ringgold, Taylor, Union | 43 min |
| May 11, 5:42 PM CDT | Tornado Warning | DMX | Union | 33 min |
| May 11, 5:44 PM CDT | Severe Thunderstorm Warning | DMX | Clarke, Decatur, Lucas, Madison, Ringgold, Warren | 46 min |
| May 11, 6:03 PM CDT | Flash Flood Warning | DMX | Union | 6 hr |
| May 11, 6:06 PM CDT | Severe Thunderstorm Warning | DMX | Adair, Clarke, Madison, Union | 54 min |
| May 11, 6:37 PM CDT | Severe Thunderstorm Warning | DMX | Dallas, Madison, Polk, Warren | 53 min |
| May 11, 6:42 PM CDT | Severe Thunderstorm Warning | DMX | Clarke, Decatur, Lucas, Warren | 48 min |
| May 11, 6:46 PM CDT | Severe Thunderstorm Warning | DMX | Wayne | 44 min |
| May 11, 7:29 PM CDT | Severe Thunderstorm Warning | DMX | Lucas, Marion, Monroe | 25 min |
| May 11, 8:24 PM CDT | Severe Thunderstorm Warning | DMX | Appanoose | 29 min |
| May 11, 8:27 PM CDT | Severe Thunderstorm Warning | DMX | Lucas, Marion, Monroe, Wayne | 48 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, 7.9 hours before the alert went out and 30 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
- 909 J/kg
- Mixed-layer CIN
- -95 J/kg
- Mixed-layer LCL
- 1123 m above ground
- 0-6 km bulk shear
- 24 kt
- 0-1 km storm-relative helicity
- 55 m²/s²
- 0-3 km storm-relative helicity
- 177 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 3.2
The text
As transmitted, in the capitals the NWS used until 2016.
638
WWUS20 KWNS 111955
SEL2
SPC WW 111955
IAZ000-NEZ000-120000-
URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 282
NWS STORM PREDICTION CENTER NORMAN OK
255 PM CDT WED MAY 11 2011
THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF
SOUTHWEST IOWA
EASTERN NEBRASKA
EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 255 PM UNTIL
700 PM CDT.
TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.
THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 155 STATUTE
MILES EAST AND WEST OF A LINE FROM 10 MILES NORTH OF DENISON IOWA
TO 20 MILES WEST SOUTHWEST OF SHENANDOAH IOWA. FOR A COMPLETE
DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE
(WOUS64 KWNS WOU2).
REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.
OTHER WATCH INFORMATION...CONTINUE...WW 278...WW 279...WW
280...WW 281...
DISCUSSION...INTENSE STORMS EXPECTED TO CONTINUE TO SPREAD NWD
ACROSS DESTABILIZING AIRMASS ALONG THE MISSOURI RIVER VALLEY. WHILE
SPEED SHEAR IN THE CLOUD-BEARING LAYER IS NOT PARTICULARLY CONDUCIVE
TO ROBUST ORGANIZATION...DEGREE OF INSTABILITY...DIRECTIONAL
SHEAR...AND STORM SCALE INTERACTIONS ARE EXPECTED TO COMPENSATE FOR
THIS SHORTCOMING AND LEAD TO AN INCREASING CHANCE FOR ENHANCED LOW
LEVEL STORM ROTATION AND POSSIBLE TORNADOES. EXPECT THIS POTENTIAL
TO UNFOLD AS STRONGER UPDRAFTS ALONG THE LEADING EDGE OF MCS COLD
POOL ENCOUNTER BACKED LOW LEVEL FLOW ACROSS ERN NEB AND SWRN IA.
AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
500. MEAN STORM MOTION VECTOR 20035.
...CARBINSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 10, 8:45 PM CDT | Mesoscale Discussion | SPC | Allamakee, Howard, Mitchell, Winneshiek, Worth | 90 min |
| May 11, 8:09 AM CDT | Mesoscale Discussion | SPC | Allamakee, Appanoose, Benton, Black Hawk, Bremer, Buchanan and 32 more | 66 min |
| May 11, 1:23 PM CDT | Severe Thunderstorm Watch | SPC | Allamakee, Benton, Buchanan, Cedar, Clayton, Clinton and 17 more | 6 hr |
| May 11, 2:31 PM CDT | Mesoscale Discussion | SPC | Adair, Adams, Audubon, Carroll, Cass, Crawford and 13 more | 59 min |
| May 11, 3:38 PM CDT | Mesoscale Discussion | SPC | Allamakee, Appanoose, Benton, Black Hawk, Buchanan, Cedar and 26 more | 2 hr |
| May 11, 5:03 PM CDT | Mesoscale Discussion | SPC | Buena Vista, Cherokee, Clay, Dickinson, Ida, Lyon and 6 more | 57 min |
| May 11, 6:17 PM CDT | Mesoscale Discussion | SPC | Appanoose, Clarke, Davis, Decatur, Jasper, Lucas and 9 more | 28 min |
| May 11, 12:16 PM CDT | Severe Thunderstorm Watch | SPC | Adams, Buffalo, Butler, Cass, Clay, Colfax and 37 more | 5 hr |
| May 11, 3:57 PM CDT | Mesoscale Discussion | SPC | Nemaha, Pawnee, Richardson | 48 min |
| May 11, 4:52 PM CDT | Tornado Watch | SPC | Dundy, Furnas, Harlan, Hitchcock, Red Willow | 6 hr |
Nearby
Tornado Watches in Iowa, 2011Tornado Watches in Nebraska, 2011Every tornado 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.