Alert archive / Iowa / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 617

September 4, 201220 counties in Iowa; 7 counties in Minnesota

The Storm Prediction Center issued this severe thunderstorm watch at Sep 4, 2012, 10:19 PM CDT for 20 counties in Iowa; 7 counties in Minnesota. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued
Sep 4, 2012, 10:19 PM CDT (03:19 UTC)
Expired
Sep 5, 2012, 3:00 AM CDT
In force
5 hr
Issued by
the Storm Prediction Center
Largest hail expected
1.5 in
Strongest gust expected
60 kt
All 27 counties

Black Hawk County, IA, Bremer County, IA, Butler County, IA, Calhoun County, IA, Cerro Gordo County, IA, Emmet County, IA, Franklin County, IA, Grundy County, IA, Hamilton County, IA, Hancock County, IA, Hardin County, IA, Humboldt County, IA, Kossuth County, IA, Palo Alto County, IA, Pocahontas County, IA, Sac County, IA, Webster County, IA, Winnebago County, IA, Worth County, IA, Wright County, IA, Blue Earth County, MN, Faribault County, MN, Freeborn County, MN, Martin County, MN, Steele County, MN, Waseca County, MN, Watonwan County, MN

The radar

The Minneapolis radar (KMPX), 165 km from the middle of the area, began a volume at 03:20 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
30%
Ten or more severe hail reports
20%
One or more hailstones of 2 inches or more
10%
Six or more combined severe hail and wind reports
70%

Warnings issued inside it

10 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

IssuedProductOfficeCountiesLasted
Sep 4, 10:22 PM CDTSevere Thunderstorm WarningDMXPalo Alto, Pocahontas23 min
Sep 4, 10:33 PM CDTSevere Thunderstorm WarningMPXMartin39 min
Sep 4, 10:44 PM CDTSevere Thunderstorm WarningDMXEmmet, Kossuth, Palo Alto46 min
Sep 4, 10:47 PM CDTSevere Thunderstorm WarningDMXHumboldt, Kossuth, Palo Alto, Pocahontas43 min
Sep 4, 11:09 PM CDTSevere Thunderstorm WarningDMXHancock, Kossuth, Winnebago51 min
Sep 4, 11:37 PM CDTSevere Thunderstorm WarningDMXCerro Gordo, Hancock, Winnebago, Worth38 min
Sep 4, 11:49 PM CDTSevere Thunderstorm WarningMPXBlue Earth, Faribault, Freeborn, Steele, Waseca56 min
Sep 5, 12:14 AM CDTSevere Thunderstorm WarningDMXCerro Gordo, Worth16 min
Sep 5, 12:14 AM CDTSevere Thunderstorm WarningDMXCalhoun, Humboldt, Pocahontas, Webster46 min
Sep 5, 1:09 AM CDTSevere Thunderstorm WarningDMXBlack Hawk, Bremer, Butler, Grundy29 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

Minneapolis, MN (KMPX), launched 00:00Z, 3.3 hours before the alert went out and 165 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.

Skew-T log-pSkew-T log-p diagram, Minneapolis, MN at 00:00Z on 2012-09-05Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Minneapolis, MN at 00:00Z on 2012-09-05The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 4 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
3109 m above ground
0-6 km bulk shear
31 kt
0-1 km storm-relative helicity
4 m²/s²
0-3 km storm-relative helicity
63 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 4, 7:27 PM CDTMesoscale DiscussionSPCBuena Vista, Cherokee, Clay, Dickinson, Lyon, O'Brien and 3 more63 min
Sep 4, 7:45 PM CDTSevere Thunderstorm WatchSPCBuena Vista, Cherokee, Clay, Dickinson, Ida, Lyon and 5 more6 hr
Sep 4, 8:30 PM CDTMesoscale DiscussionSPCAllamakee, Black Hawk, Bremer, Buchanan, Butler, Chickasaw and 8 more60 min
Sep 4, 8:51 PM CDTSevere Thunderstorm WatchSPCBuchanan, Clinton, Delaware, Dubuque, Jackson, Jones5 hr
Sep 4, 9:51 PM CDTMesoscale DiscussionSPCBuena Vista, Calhoun, Cerro Gordo, Clay, Dickinson, Emmet and 12 more54 min
Sep 4, 11:16 PM CDTSevere Thunderstorm WatchSPCAllamakee, Chickasaw, Clayton, Fayette, Floyd, Howard and 2 more4 hr
Sep 5, 1:14 AM CDTMesoscale DiscussionSPCAllamakee, Audubon, Benton, Black Hawk, Boone, Bremer and 54 more91 min
Sep 5, 3:43 AM CDTMesoscale DiscussionSPCBenton, Cedar, Clinton, Des Moines, Dubuque, Henry and 14 more92 min

Nearby

Severe Thunderstorm Watches in Iowa, 2012Severe Thunderstorm Watches in Minnesota, 2012Every severe thunderstorm watch in 2012

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.