Alert archive / Nebraska / Tornado Watches in 2007

Tornado Watch 631

August 21, 200720 counties in Nebraska; 10 counties in South Dakota

The Storm Prediction Center issued this tornado watch at Aug 21, 2007, 3:45 PM CDT for 20 counties in Nebraska; 10 counties in South Dakota. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Aug 21, 2007, 3:45 PM CDT (20:45 UTC)
Expired: Aug 21, 2007, 10:00 PM CDT
In force: 6 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2.5 in
Strongest gust expected: 60 kt

All 30 counties

Antelope County, NE, Boone County, NE, Boyd County, NE, Cedar County, NE, Colfax County, NE, Cuming County, NE, Dakota County, NE, Dixon County, NE, Garfield County, NE, Holt County, NE, Knox County, NE, Loup County, NE, Madison County, NE, Pierce County, NE, Platte County, NE, Rock County, NE, Stanton County, NE, Thurston County, NE, Wayne County, NE, Wheeler County, NE, Bon Homme County, SD, Charles Mix County, SD, Clay County, SD, Douglas County, SD, Gregory County, SD, Hutchinson County, SD, Lincoln County, SD, Turner County, SD, Union County, SD, Yankton County, SD

The radar

The Sioux Falls radar (KFSD), 158 km from the middle of the area, began a volume at 20:46 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: 50%
One or more hailstones of 2 inches or more: 40%
Six or more combined severe hail and wind reports: 80%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Aug 21, 5:03 PM CDT	Severe Thunderstorm Warning	FSD	Charles Mix	57 min
Aug 21, 5:21 PM CDT	Severe Thunderstorm Warning	LBF	Holt	24 min
Aug 21, 5:40 PM CDT	Severe Thunderstorm Warning	FSD	Douglas	50 min
Aug 21, 5:44 PM CDT	Severe Thunderstorm Warning	LBF	Holt	46 min
Aug 21, 5:46 PM CDT	Tornado Warning	FSD	Charles Mix	44 min
Aug 21, 5:56 PM CDT	Severe Thunderstorm Warning	FSD	Bon Homme	64 min
Aug 21, 6:02 PM CDT	Severe Thunderstorm Warning	FSD	Hutchinson	32 min
Aug 21, 6:03 PM CDT	Tornado Warning	LBF	Holt	27 min
Aug 21, 6:12 PM CDT	Tornado Warning	FSD	Bon Homme	48 min
Aug 21, 6:14 PM CDT	Severe Thunderstorm Warning	OAX	Knox	61 min
Aug 21, 6:28 PM CDT	Tornado Warning	LBF	Holt, Wheeler	32 min
Aug 21, 6:36 PM CDT	Severe Thunderstorm Warning	FSD	Charles Mix	39 min
Aug 21, 6:43 PM CDT	Severe Thunderstorm Warning	LBF	Garfield	47 min
Aug 21, 6:56 PM CDT	Severe Thunderstorm Warning	FSD	Bon Homme	49 min
Aug 21, 6:58 PM CDT	Severe Thunderstorm Warning	LBF	Holt, Wheeler	62 min
Aug 21, 7:10 PM CDT	Severe Thunderstorm Warning	FSD	Yankton	65 min
Aug 21, 7:14 PM CDT	Severe Thunderstorm Warning	OAX	Knox	44 min
Aug 21, 7:26 PM CDT	Severe Thunderstorm Warning	LBF	Garfield	49 min
Aug 21, 7:33 PM CDT	Tornado Warning	OAX	Cedar	42 min
Aug 21, 7:35 PM CDT	Severe Thunderstorm Warning	FSD	Dakota	55 min
Aug 21, 7:47 PM CDT	Severe Thunderstorm Warning	FSD	Dixon	43 min
Aug 21, 7:53 PM CDT	Severe Thunderstorm Warning	OAX	Pierce	52 min
Aug 21, 7:57 PM CDT	Severe Thunderstorm Warning	LBF	Wheeler	33 min
Aug 21, 8:03 PM CDT	Severe Thunderstorm Warning	OAX	Boone	42 min
Aug 21, 8:12 PM CDT	Severe Thunderstorm Warning	LBF	Garfield	48 min
Aug 21, 8:21 PM CDT	Severe Thunderstorm Warning	FSD	Union	24 min
Aug 21, 8:40 PM CDT	Severe Thunderstorm Warning	OAX	Madison, Platte	65 min
Aug 21, 8:44 PM CDT	Severe Thunderstorm Warning	OAX	Boone	31 min
Aug 21, 9:11 PM CDT	Severe Thunderstorm Warning	OAX	Stanton	29 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, 8.8 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.

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: 174 J/kg
Mixed-layer CIN: -479 J/kg
Mixed-layer LCL: 1438 m above ground
0-6 km bulk shear: 21 kt
0-1 km storm-relative helicity: 46 m²/s²
0-3 km storm-relative helicity: 61 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.

Issued	Product	Office	Counties	Lasted
Aug 20, 7:03 PM CDT	Mesoscale Discussion	SPC	Cedar	117 min
Aug 20, 7:35 PM CDT	Mesoscale Discussion	SPC	Burt, Butler, Cass, Clay, Colfax, Cuming and 27 more	85 min
Aug 21, 2:47 PM CDT	Mesoscale Discussion	SPC	Antelope, Blaine, Boone, Boyd, Brown, Buffalo and 44 more	118 min
Aug 21, 3:50 PM CDT	Severe Thunderstorm Watch	SPC	Adams, Buffalo, Custer, Dawson, Franklin, Frontier and 16 more	6 hr
Aug 21, 5:53 PM CDT	Mesoscale Discussion	SPC	Buffalo, Dawson, Frontier, Furnas, Gosper, Harlan and 5 more	97 min
Aug 21, 6:17 PM CDT	Mesoscale Discussion	SPC	Antelope, Boone, Burt, Cedar, Colfax, Cuming and 11 more	88 min
Aug 21, 6:47 PM CDT	Tornado Watch	SPC	Burt, Dodge, Washington	7 hr

Nearby

Tornado Watches in Nebraska, 2007 Tornado Watches in South Dakota, 2007 Every tornado watch in 2007

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.