Alert archive / Nebraska / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 221

May 1, 20126 counties in Iowa; 34 counties in Nebraska; 6 counties in South Dakota

The Storm Prediction Center issued this severe thunderstorm watch at May 1, 2012, 4:58 PM CDT for 6 counties in Iowa; 34 counties in Nebraska; 6 counties in South Dakota. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: May 1, 2012, 4:58 PM CDT (21:58 UTC)
Expired: May 1, 2012, 9:20 PM CDT
In force: 4 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

All 46 counties

Buena Vista County, IA, Cherokee County, IA, Ida County, IA, Monona County, IA, Plymouth County, IA, Woodbury County, IA, Antelope County, NE, Blaine County, NE, Boone County, NE, Boyd County, NE, Brown County, NE, Burt County, NE, Cedar County, NE, Colfax County, NE, Cuming County, NE, Custer County, NE, Dakota County, NE, Dixon County, NE, Dodge County, NE, Garfield County, NE, Greeley County, NE, Holt County, NE, Howard County, NE, Keya Paha County, NE, Knox County, NE, Logan County, NE, Loup County, NE, Madison County, NE, Merrick County, NE, Nance County, NE, Pierce County, NE, Platte County, NE, Rock County, NE, Sherman County, NE, Stanton County, NE, Thomas County, NE, Thurston County, NE, Valley County, NE, Wayne County, NE, Wheeler County, NE, Aurora County, SD, Brule County, SD, Charles Mix County, SD, Davison County, SD, Douglas County, SD, Gregory County, SD

The radar

The Sioux Falls radar (KFSD), 153 km from the middle of the area, began a volume at 21:58 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: 10%
Ten or more severe hail reports: 60%
One or more hailstones of 2 inches or more: 20%
Six or more combined severe hail and wind reports: 90%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
May 1, 4:58 PM CDT	Severe Thunderstorm Warning	LBF	Brown, Rock	62 min
May 1, 5:46 PM CDT	Severe Thunderstorm Warning	LBF	Holt, Rock	48 min
May 1, 6:31 PM CDT	Severe Thunderstorm Warning	LBF	Rock	44 min
May 1, 7:25 PM CDT	Severe Thunderstorm Warning	LBF	Holt	21 min
May 1, 9:15 PM CDT	Severe Thunderstorm Warning	FSD	Buena Vista, Cherokee, Clay, O'Brien, Plymouth, Sioux	30 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, 10.0 hours before the alert went out and 211 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: 47 J/kg
Mixed-layer CIN: -229 J/kg
Mixed-layer LCL: 653 m above ground
0-6 km bulk shear: 29 kt
0-1 km storm-relative helicity: 196 m²/s²
0-3 km storm-relative helicity: 190 m²/s²
Significant tornado parameter: 0.0
Supercell composite: -0.1

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

908 
WWUS20 KWNS 012202
SEL1
SPC WW 012202
IAZ000-NEZ000-SDZ000-020600-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 221
NWS STORM PREDICTION CENTER NORMAN OK
500 PM CDT TUE MAY 1 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

       NORTHWEST IOWA
       CENTRAL THROUGH NORTHEASTERN NEBRASKA
       SOUTHEAST SOUTH DAKOTA

EFFECTIVE THIS TUESDAY AFTERNOON AND WEDNESDAY MORNING FROM 500
PM UNTIL 100 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 115
STATUTE MILES EAST AND WEST OF A LINE FROM 45 MILES NORTH
NORTHEAST OF YANKTON SOUTH DAKOTA TO 35 MILES SOUTHEAST OF
BURWELL NEBRASKA.  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 217...WW 218...WW
219...WW 220...

DISCUSSION...TSTMS EXPECTED TO DEVELOP SWD ALONG NE-SE COLD FRONT
NOW CROSSING SE SD/CNTRL SD AS SFC HEATING CONTINUES TO DESTABILIZE
REGION TO ITS SE.  DEEP SHEAR AND INSTABILITY SHOULD BE SUFFICIENT
FOR A FEW SUSTAINED STORMS/SUPERCELLS WITH LARGE HAIL AND DMGG WIND.
ADDITIONAL...POSSIBLY SEPARATE STORM DEVELOPMENT MAY OCCUR LATER
THIS EVE OVER S CNTRL AND ERN NEB AS SLY LLJ BROADENS AND
STRENGTHENS IN RESPONSE TO DIURNAL CYCLE AND APPROACH OF CNTRL RCKYS
UPR IMPULSE.

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 550. MEAN STORM
MOTION VECTOR 26030.


...CORFIDI

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 1, 2:30 PM CDT	Mesoscale Discussion	SPC	Cherokee, Clay, Dickinson, Emmet, Lyon, O'Brien and 4 more	60 min
May 1, 2:59 PM CDT	Tornado Watch	SPC	Clay, Dickinson, Lyon, O'Brien, Osceola, Sioux	6 hr
May 1, 6:11 PM CDT	Mesoscale Discussion	SPC	Clay, Dickinson, Emmet, Kossuth, Lyon, O'Brien and 3 more	94 min

Nearby

Severe Thunderstorm Watches in Nebraska, 2012 Severe Thunderstorm Watches in Iowa, 2012 Severe Thunderstorm Watches in South Dakota, 2012 Every 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.