Alert archive / Iowa / Severe Thunderstorm Watches in 2011

Severe Thunderstorm Watch 785

August 18, 201123 counties in Iowa; 23 counties in Nebraska

The Storm Prediction Center issued this severe thunderstorm watch at Aug 18, 2011, 1:27 PM CDT for 23 counties in Iowa; 23 counties in Nebraska. It was in force for 8 hr.

The area

The outline as issued.

The facts

Issued: Aug 18, 2011, 1:27 PM CDT (18:27 UTC)
Expired: Aug 18, 2011, 9:00 PM CDT
In force: 8 hr
Issued by: the Storm Prediction Center
Largest hail expected: 3 in
Strongest gust expected: 60 kt

All 46 counties

Adair County, IA, Adams County, IA, Audubon County, IA, Carroll County, IA, Cass County, IA, Cherokee County, IA, Crawford County, IA, Fremont County, IA, Guthrie County, IA, Harrison County, IA, Ida County, IA, Mills County, IA, Monona County, IA, Montgomery County, IA, Page County, IA, Plymouth County, IA, Pottawattamie County, IA, Ringgold County, IA, Sac County, IA, Shelby County, IA, Taylor County, IA, Union County, IA, Woodbury County, IA, Antelope County, NE, Boone County, NE, Burt County, NE, Cass County, NE, Cedar County, NE, Colfax County, NE, Cuming County, NE, Dakota County, NE, Dixon County, NE, Dodge County, NE, Douglas County, NE, Knox County, NE, Lancaster County, NE, Madison County, NE, Otoe County, NE, Pierce County, NE, Platte County, NE, Sarpy County, NE, Saunders County, NE, Stanton County, NE, Thurston County, NE, Washington County, NE, Wayne County, NE

The radar

The Omaha radar (KOAX), 49 km from the middle of the area, began a volume at 18:30 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: 70%
One or more hailstones of 2 inches or more: 40%
Six or more combined severe hail and wind reports: 80%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Aug 18, 1:43 PM CDT	Severe Thunderstorm Warning	FSD	Dakota, Dixon	62 min
Aug 18, 2:00 PM CDT	Severe Thunderstorm Warning	FSD	Ida, Woodbury	45 min
Aug 18, 2:08 PM CDT	Severe Thunderstorm Warning	OAX	Monona	37 min
Aug 18, 2:13 PM CDT	Severe Thunderstorm Warning	DMX	Crawford	47 min
Aug 18, 2:48 PM CDT	Severe Thunderstorm Warning	FSD	Woodbury	27 min
Aug 18, 3:14 PM CDT	Severe Thunderstorm Warning	OAX	Cedar	46 min
Aug 18, 3:15 PM CDT	Severe Thunderstorm Warning	FSD	Woodbury	18 min
Aug 18, 3:34 PM CDT	Severe Thunderstorm Warning	OAX	Harrison, Shelby	41 min
Aug 18, 3:42 PM CDT	Severe Thunderstorm Warning	FSD	Dixon	48 min
Aug 18, 3:44 PM CDT	Severe Thunderstorm Warning	OAX	Burt, Dodge, Washington	46 min
Aug 18, 3:57 PM CDT	Severe Thunderstorm Warning	OAX	Pierce, Wayne	63 min
Aug 18, 3:59 PM CDT	Severe Thunderstorm Warning	OAX	Cedar	20 min
Aug 18, 4:07 PM CDT	Severe Thunderstorm Warning	OAX	Pottawattamie, Shelby	38 min
Aug 18, 4:17 PM CDT	Severe Thunderstorm Warning	OAX	Harrison	43 min
Aug 18, 4:26 PM CDT	Severe Thunderstorm Warning	FSD	Dakota, Dixon	49 min
Aug 18, 4:44 PM CDT	Severe Thunderstorm Warning	OAX	Pottawattamie	46 min
Aug 18, 4:48 PM CDT	Severe Thunderstorm Warning	OAX	Antelope, Knox	57 min
Aug 18, 4:53 PM CDT	Severe Thunderstorm Warning	OAX	Monona	52 min
Aug 18, 4:56 PM CDT	Severe Thunderstorm Warning	OAX	Harrison, Pottawattamie	49 min
Aug 18, 5:00 PM CDT	Severe Thunderstorm Warning	FSD	Woodbury	45 min
Aug 18, 5:20 PM CDT	Severe Thunderstorm Warning	OAX	Mills, Pottawattamie	40 min
Aug 18, 5:22 PM CDT	Severe Thunderstorm Warning	FSD	Dakota, Dixon	23 min
Aug 18, 5:25 PM CDT	Severe Thunderstorm Warning	OAX	Montgomery, Pottawattamie	50 min
Aug 18, 5:25 PM CDT	Tornado Warning	OAX	Antelope	50 min
Aug 18, 5:28 PM CDT	Severe Thunderstorm Warning	OAX	Cedar	47 min
Aug 18, 5:37 PM CDT	Severe Thunderstorm Warning	OAX	Antelope, Knox, Pierce	38 min
Aug 18, 5:41 PM CDT	Flash Flood Warning	OAX	Harrison, Pottawattamie	5 hr
Aug 18, 5:43 PM CDT	Severe Thunderstorm Warning	OAX	Monona	47 min
Aug 18, 5:46 PM CDT	Severe Thunderstorm Warning	FSD	Dakota, Dixon	29 min
Aug 18, 5:50 PM CDT	Flash Flood Warning	OAX	Monona	6 hr
Aug 18, 5:52 PM CDT	Severe Thunderstorm Warning	OAX	Fremont, Mills, Pottawattamie	38 min
Aug 18, 5:57 PM CDT	Severe Thunderstorm Warning	FSD	Dixon	33 min
Aug 18, 5:58 PM CDT	Severe Thunderstorm Warning	OAX	Montgomery, Page	28 min
Aug 18, 6:01 PM CDT	Tornado Warning	OAX	Antelope, Knox	44 min
Aug 18, 6:05 PM CDT	Severe Thunderstorm Warning	DMX	Adams, Taylor	40 min
Aug 18, 6:08 PM CDT	Tornado Warning	OAX	Antelope	52 min
Aug 18, 6:15 PM CDT	Severe Thunderstorm Warning	OAX	Monona	45 min
Aug 18, 6:16 PM CDT	Severe Thunderstorm Warning	OAX	Fremont, Mills, Montgomery, Page	44 min
Aug 18, 6:25 PM CDT	Flash Flood Warning	OAX	Antelope	3 hr
Aug 18, 6:26 PM CDT	Severe Thunderstorm Warning	FSD	Dakota, Dixon	34 min
Aug 18, 6:28 PM CDT	Flash Flood Warning	FSD	Dakota	4 hr
Aug 18, 6:35 PM CDT	Severe Thunderstorm Warning	DMX	Taylor	40 min
Aug 18, 6:40 PM CDT	Severe Thunderstorm Warning	OAX	Page	38 min
Aug 18, 6:42 PM CDT	Severe Thunderstorm Warning	OAX	Harrison, Pottawattamie, Shelby	48 min
Aug 18, 6:56 PM CDT	Severe Thunderstorm Warning	OAX	Burt, Cuming, Dodge, Thurston	33 min
Aug 18, 6:57 PM CDT	Tornado Warning	OAX	Antelope, Boone, Madison	32 min
Aug 18, 7:02 PM CDT	Flash Flood Warning	FSD	Woodbury	98 min
Aug 18, 7:02 PM CDT	Tornado Warning	OAX	Knox	31 min
Aug 18, 7:08 PM CDT	Severe Thunderstorm Warning	DMX	Audubon, Cass	52 min
Aug 18, 7:14 PM CDT	Severe Thunderstorm Warning	DMX	Taylor	16 min
Aug 18, 7:15 PM CDT	Severe Thunderstorm Warning	OAX	Harrison, Pottawattamie, Shelby	45 min
Aug 18, 7:21 PM CDT	Tornado Warning	OAX	Antelope, Boone, Madison	39 min
Aug 18, 7:25 PM CDT	Severe Thunderstorm Warning	OAX	Antelope, Madison, Stanton	35 min
Aug 18, 7:36 PM CDT	Severe Thunderstorm Warning	OAX	Mills	39 min
Aug 18, 7:45 PM CDT	Tornado Warning	OAX	Boone, Butler, Madison, Platte	30 min
Aug 18, 7:47 PM CDT	Severe Thunderstorm Warning	OAX	Cass, Lancaster, Sarpy, Saunders	43 min
Aug 18, 7:58 PM CDT	Severe Thunderstorm Warning	OAX	Fremont, Mills, Page	47 min
Aug 18, 8:11 PM CDT	Severe Thunderstorm Warning	OAX	Cass, Lancaster, Otoe	49 min
Aug 18, 8:18 PM CDT	Severe Thunderstorm Warning	OAX	Boone, Butler, Colfax, Platte	42 min
Aug 18, 8:23 PM CDT	Severe Thunderstorm Warning	OAX	Fremont, Page	52 min
Aug 18, 8:34 PM CDT	Flash Flood Warning	OAX	Fremont, Mills, Pottawattamie	6 hr
Aug 18, 8:40 PM CDT	Flash Flood Warning	OAX	Platte	77 min
Aug 18, 8:55 PM CDT	Severe Thunderstorm Warning	OAX	Cass, Gage, Johnson, Lancaster, Nemaha, Otoe	38 min
Aug 18, 8:59 PM CDT	Severe Thunderstorm Warning	DMX	Taylor	46 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, 6.5 hours before the alert went out and 49 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 1181 J/kg
Mixed-layer CIN: -126 J/kg
Mixed-layer LCL: 683 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 234 m²/s²
0-3 km storm-relative helicity: 385 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 11.7

Open this sounding in Storm Lab

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 18, 12:31 PM CDT	Mesoscale Discussion	SPC	Crawford, Harrison, Ida, Mills, Monona, Plymouth and 3 more	89 min
Aug 18, 2:51 PM CDT	Mesoscale Discussion	SPC	Adair, Adams, Audubon, Cass, Fremont, Guthrie and 9 more	84 min
Aug 18, 6:18 PM CDT	Mesoscale Discussion	SPC	Fremont, Harrison, Mills, Monona, Montgomery, Page and 2 more	27 min
Aug 18, 6:38 PM CDT	Tornado Watch	SPC	Fremont, Mills, Page	5 hr
Aug 17, 9:18 PM CDT	Mesoscale Discussion	SPC	Blaine, Brown, Chase, Cherry, Dundy, Frontier and 10 more	57 min
Aug 18, 6:00 PM CDT	Mesoscale Discussion	SPC	Johnson, Nemaha, Pawnee, Richardson	60 min

Nearby

Severe Thunderstorm Watches in Iowa, 2011 Severe Thunderstorm Watches in Nebraska, 2011 Every 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.