Alert archive / Iowa / Tornado Warnings in 2011
Tornado Warning 20, NWS Sioux Falls, SD
NWS Sioux Falls, SD issued this tornado warning at May 11, 2011, 6:37 PM CDT for Lyon County, Sioux County, Iowa. It was in force for 23 min. 1 report came from inside the area while it was in force.
The area
The outline as issued, with what was reported inside it.
The facts
- Issued
- May 11, 2011, 6:37 PM CDT (23:37 UTC)
- Expired
- May 11, 2011, 7:00 PM CDT
- In force
- 23 min
- Issued by
- NWS Sioux Falls, SD
- Area
- Storm-based polygon
Counties Lyon County, IA, Sioux County, IA
The radar
The Sioux Falls radar (KFSD), 50 km from the middle of the area, began a volume at 23:41 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 was reported inside it
| Time | Report | Where | Remark |
|---|---|---|---|
| May 11, 6:53 PM CDT | TORNADO | 4 S George, IA | TRAINED SPOTTER ONE MILE SOUTH OF ASHTON, LOOKING WEST AT A THIN ROPE TORNADO PICKING UP DUST NEAR GEORGE. |
Local storm reports filed while the alert was in force, from inside its polygon or its counties.
The nearest sounding before it
Omaha, NE (KOAX), launched 12:00Z, 11.6 hours before the alert went out and 223 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.
244 WFUS53 KFSD 112337 TORFSD IAC119-167-120000- /O.NEW.KFSD.TO.W.0020.110511T2337Z-110512T0000Z/ BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING NATIONAL WEATHER SERVICE SIOUX FALLS SD 637 PM CDT WED MAY 11 2011 THE NATIONAL WEATHER SERVICE IN SIOUX FALLS HAS ISSUED A * TORNADO WARNING FOR... CENTRAL LYON COUNTY IN NORTHWEST IOWA... NORTH CENTRAL SIOUX COUNTY IN NORTHWEST IOWA... * UNTIL 700 PM CDT * AT 637 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS WERE TRACKING A SEVERE THUNDERSTORM PRODUCING A BRIEF TORNADO BETWEEN ROCK VALLEY AND OON. DOPPLER RADAR SHOWED A BRIEF TORNADO MOVING NORTHEAST AT 20 MPH. * THIS TORNADIC STORM WILL BE NEAR... ALVORD AROUND 645 PM CDT... PRECAUTIONARY/PREPAREDNESS ACTIONS... TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE OR OUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT YOURSELF FROM FLYING DEBRIS. && LAT...LON 4347 9625 4330 9594 4316 9629 4323 9639 TIME...MOT...LOC 2337Z 216DEG 19KT 4326 9625 $$ LAFLIN
2 follow-up statements
242 WFUS53 KFSD 112339 CCA TORFSD IAC119-167-120000- /O.COR.KFSD.TO.W.0020.110511T2337Z-110512T0000Z/ BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING...CORRECTED NATIONAL WEATHER SERVICE SIOUX FALLS SD 637 PM CDT WED MAY 11 2011 THE NATIONAL WEATHER SERVICE IN SIOUX FALLS HAS ISSUED A * TORNADO WARNING FOR... CENTRAL LYON COUNTY IN NORTHWEST IOWA... NORTH CENTRAL SIOUX COUNTY IN NORTHWEST IOWA... * UNTIL 700 PM CDT * AT 637 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS WERE TRACKING A SEVERE THUNDERSTORM PRODUCING A BRIEF TORNADO BETWEEN ROCK VALLEY AND DOON. DOPPLER RADAR SHOWED A BRIEF TORNADO MOVING NORTHEAST AT 20 MPH. * THIS TORNADIC STORM WILL BE NEAR... ALVORD AROUND 645 PM CDT... PRECAUTIONARY/PREPAREDNESS ACTIONS... TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE OR OUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT YOURSELF FROM FLYING DEBRIS. && LAT...LON 4347 9625 4330 9594 4316 9629 4323 9639 TIME...MOT...LOC 2337Z 216DEG 19KT 4326 9625 $$ LAFLIN
275 WWUS53 KFSD 112351 SVSFSD SEVERE WEATHER STATEMENT NATIONAL WEATHER SERVICE SIOUX FALLS SD 651 PM CDT WED MAY 11 2011 IAC119-167-120000- /O.CON.KFSD.TO.W.0020.000000T0000Z-110512T0000Z/ LYON IA-SIOUX IA- 651 PM CDT WED MAY 11 2011 ...A TORNADO WARNING REMAINS IN EFFECT FOR NORTH CENTRAL SIOUX AND CENTRAL LYON COUNTIES UNTIL 700 PM CDT... AT 651 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS WERE TRACKING A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A BRIEF TORNADO. THIS STORM WAS LOCATED NEAR DOON...OR 8 MILES SOUTH OF ROCK RAPIDS...MOVING NORTHEAST AT 20 MPH. THIS TORNADO WILL AFFECT MAINLY RURAL AREAS OF CENTRAL LYON AND NORTH CENTRAL SIOUX COUNTIES. PRECAUTIONARY/PREPAREDNESS ACTIONS... TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE OR OUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT YOURSELF FROM FLYING DEBRIS. && LAT...LON 4347 9625 4330 9594 4316 9629 4323 9639 TIME...MOT...LOC 2351Z 216DEG 19KT 4332 9619 $$ LAFLIN
The office that day
Everything else NWS Sioux Falls, SD issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 11, 4:55 PM CDT | Severe Thunderstorm Warning | FSD | Plymouth, Woodbury | 50 min |
| May 11, 5:37 PM CDT | Severe Thunderstorm Warning | FSD | Plymouth | 38 min |
| May 11, 5:42 PM CDT | Severe Thunderstorm Warning | FSD | Plymouth, Sioux, Woodbury | 48 min |
| May 11, 5:48 PM CDT | Severe Thunderstorm Warning | FSD | Lyon, Sioux | 42 min |
| May 11, 6:49 PM CDT | Severe Thunderstorm Warning | FSD | Lyon, Sioux | 41 min |
| May 11, 6:58 PM CDT | Tornado Warning | FSD | Dickinson, Lyon, O'Brien, Osceola | 32 min |
Nearby
Tornado Warnings in Iowa, 2011Every tornado warning in 2011Tornadoes 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.