Alert archive / Iowa / Severe Thunderstorm Watches in 2011
Severe Thunderstorm Watch 521
The Storm Prediction Center issued this severe thunderstorm watch at Jun 20, 2011, 3:46 AM CDT for 32 counties in Iowa; 16 counties in Nebraska. It was in force for 5 hr.
The area
The outline as issued.
The facts
- Issued
- Jun 20, 2011, 3:46 AM CDT (08:46 UTC)
- Expired
- Jun 20, 2011, 8:46 AM CDT
- In force
- 5 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 2 in
- Strongest gust expected
- 60 kt
All 48 counties
Adair County, IA, Audubon County, IA, Black Hawk County, IA, Boone County, IA, Calhoun County, IA, Carroll County, IA, Cass County, IA, Crawford County, IA, Dallas County, IA, Greene County, IA, Grundy County, IA, Guthrie County, IA, Hamilton County, IA, Hardin County, IA, Harrison County, IA, Jasper County, IA, Madison County, IA, Mahaska County, IA, Marion County, IA, Marshall County, IA, Mills County, IA, Monona County, IA, Montgomery County, IA, Polk County, IA, Pottawattamie County, IA, Poweshiek County, IA, Sac County, IA, Shelby County, IA, Story County, IA, Tama County, IA, Warren County, IA, Webster County, IA, Burt County, NE, Butler County, NE, Cass County, NE, Colfax County, NE, Cuming County, NE, Dodge County, NE, Douglas County, NE, Lancaster County, NE, Madison County, NE, Platte County, NE, Sarpy County, NE, Saunders County, NE, Seward County, NE, Stanton County, NE, Thurston County, NE, Washington County, NE
The radar
The Omaha radar (KOAX), 96 km from the middle of the area, began a volume at 08:49 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
- 5%
- Ten or more severe wind reports
- 30%
- One or more gusts of 65 knots or more
- 30%
- Ten or more severe hail reports
- 30%
- One or more hailstones of 2 inches or more
- 20%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
2 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jun 20, 3:55 AM CDT | Severe Thunderstorm Warning | OAX | Butler, Colfax, Platte, Seward | 50 min |
| Jun 20, 6:40 AM CDT | Severe Thunderstorm Warning | DMX | Marion, Warren | 37 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 00:00Z, 8.8 hours before the alert went out and 97 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
- 2452 J/kg
- Mixed-layer CIN
- -12 J/kg
- Mixed-layer LCL
- 1426 m above ground
- 0-6 km bulk shear
- 39 kt
- 0-1 km storm-relative helicity
- -15 m²/s²
- 0-3 km storm-relative helicity
- 106 m²/s²
- Significant tornado parameter
- 0.2
- Supercell composite
- 2.2
The text
As transmitted, in the capitals the NWS used until 2016.
397
WWUS20 KWNS 200842
SEL1
SPC WW 200842
IAZ000-NEZ000-201500-
URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 521
NWS STORM PREDICTION CENTER NORMAN OK
345 AM CDT MON JUN 20 2011
THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
CENTRAL AND WESTERN IOWA
EASTERN NEBRASKA
EFFECTIVE THIS MONDAY MORNING FROM 345 AM UNTIL 1000 AM CDT.
HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.
THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 40
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 5 MILES SOUTH
SOUTHWEST OF COLUMBUS NEBRASKA TO 30 MILES SOUTH OF WATERLOO
IOWA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED
WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).
REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.
OTHER WATCH INFORMATION...CONTINUE...WW 518...WW 519...
DISCUSSION...SCATTERED STRONG TO SEVERE THUNDERSTORMS PERSIST OVER
EASTERN NEB AND WESTERN IA. THESE STORMS WILL CONTINUE TO TRACK
EASTWARD ALONG BAROCLINIC ZONE...WITH AMPLE MOISTURE/INSTABILITY
BEING FED FROM THE SOUTH. LARGE HAIL APPEARS TO BE THE MAIN THREAT
WITH THESE STORMS.
AVIATION...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 27035.
...HARTSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jun 19, 9:16 PM CDT | Mesoscale Discussion | SPC | Adair, Adams, Appanoose, Audubon, Boone, Carroll and 31 more | 59 min |
| Jun 19, 9:49 PM CDT | Tornado Watch | SPC | Fremont, Harrison, Mills, Monona, Montgomery, Page and 2 more | 6 hr |
| Jun 19, 11:42 PM CDT | Severe Thunderstorm Watch | SPC | Benton, Cedar, Clinton, Des Moines, Henry, Iowa and 10 more | 6 hr |
| Jun 20, 1:40 AM CDT | Mesoscale Discussion | SPC | Adair, Adams, Appanoose, Audubon, Boone, Carroll and 24 more | 35 min |
| Jun 20, 3:27 AM CDT | Mesoscale Discussion | SPC | Adair, Adams, Appanoose, Audubon, Boone, Carroll and 28 more | 33 min |
| Jun 20, 4:08 AM CDT | Mesoscale Discussion | SPC | Benton, Cedar, Clinton, Davis, Des Moines, Henry and 12 more | 67 min |
| Jun 20, 7:29 AM CDT | Mesoscale Discussion | SPC | Black Hawk, Grundy, Hamilton, Hardin, Jasper, Mahaska and 6 more | 61 min |
| Jun 20, 3:08 PM CDT | Tornado Watch | SPC | Audubon, Carroll, Cass, Crawford, Fremont, Harrison and 6 more | 7 hr |
| Jun 20, 5:55 PM CDT | Mesoscale Discussion | SPC | Adair, Audubon, Boone, Calhoun, Carroll, Dallas and 15 more | 65 min |
| Jun 20, 6:17 PM CDT | Mesoscale Discussion | SPC | Fremont, Harrison, Mills, Monona, Plymouth, Woodbury | 58 min |
| Jun 20, 6:53 PM CDT | Tornado Watch | SPC | Adair, Adams, Audubon, Boone, Buena Vista, Calhoun and 41 more | 6 hr |
| Jun 19, 8:24 PM CDT | Mesoscale Discussion | SPC | Adams, Blaine, Boone, Buffalo, Chase, Clay and 35 more | 96 min |
| Jun 20, 12:45 AM CDT | Severe Thunderstorm Watch | SPC | Chase, Dundy, Frontier, Hayes, Hitchcock, Red Willow | 2 hr |
| Jun 20, 8:05 AM CDT | Mesoscale Discussion | SPC | Furnas, Red Willow | 55 min |
| Jun 20, 8:38 AM CDT | Severe Thunderstorm Watch | SPC | Adams, Buffalo, Dawson, Franklin, Frontier, Furnas and 8 more | 6 hr |
| Jun 20, 12:22 PM CDT | Mesoscale Discussion | SPC | Adams, Boone, Buffalo, Clay, Custer, Dawson and 17 more | 83 min |
| Jun 20, 1:00 PM CDT | Tornado Watch | SPC | Adams, Antelope, Boone, Buffalo, Butler, Clay and 34 more | 10 hr |
| Jun 20, 2:19 PM CDT | Mesoscale Discussion | SPC | Adams, Boone, Buffalo, Clay, Dawson, Franklin and 17 more | 86 min |
| Jun 20, 2:52 PM CDT | Mesoscale Discussion | SPC | Hayes, Hitchcock, Lincoln, Logan, Red Willow | 53 min |
| Jun 20, 3:59 PM CDT | Mesoscale Discussion | SPC | Adams, Antelope, Boone, Buffalo, Clay, Custer and 21 more | 61 min |
Nearby
Severe Thunderstorm Watches in Iowa, 2011Severe Thunderstorm Watches in Nebraska, 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.