EF0 tornado, (Czd)Cozad Muni Arpt, Nebraska, May 30, 2011

1. EF065 to 85 mphthis tornado

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. EF186 to 110 mph

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. EF2111 to 135 mph

   Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.

4. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. EF5over 200 mph

   Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.

7. Unrated

   The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

Rating

EF0

Date

May 30, 2011

Touchdown

7:34 PM CDT (00:34 UTC)

Lifted

7:36 PM CDT (00:36 UTC)

On the ground

2 minutes

Path length

0.4 miles (0.6 km)

Path width

25 yards (23 m)

Deaths

0

Injuries

0

County

Dawson County

Touchdown point

40.890, -100.031

Lift-off point

40.891, -100.025

Record number

1105301834-01

The evening hours of Memorial Day 2011 featured the most widespread damaging wind event of the spring severe weather season across South Central Nebraska, as a narrow, intense line of storms marched from west to east across the entire area. Along nearly the entire length of this north-south oriented squall line were estimated or measured wind gusts of 60-80 MPH, with automated equipment at the Lexington airport recording the highest-known measured gust of 90 MPH. As a result, widespread wind damage primarily to trees, power lines and outbuildings occurred across multiple counties. Although there several preliminary reports of brief tornadoes along the leading edge of the squall line, including one near Cozad early in the evening, radar data along with photographic and video evidence suggests that the vast majority of these reports were actually gustnadoes, which are brief, but sometimes strong circulations associated with outflow and not connected to cloud base rotation. Most of these gustnado reports focused west of the Highway 281 corridor. In addition, there were also sporadic reports of quarter size hail, but damaging straight-line wind along the surging outflow was the main story by far. Just to name a few, wind highlights included: a measured 74 MPH gust at Central Nebraska Regional Airport in Grand Island with several reports of structural damage within the city including a destroyed mini-storage building; a measured gust to 83 MPH at the Ord airport with considerable damage to a hangar; three empty grain bins blown off their foundations and an unsecured trailer rolled near Strang in Fillmore County. ||Focusing on timing, the initial severe storm development took place across north central Nebraska during mid-afternoon, with the developing severe squall line first creeping southward into western Dawson County around 7 PM CDT. Thereafter, the line continued to build south into Kansas as it marched east, crossing the Highway 281 corridor mainly between 9 and 10 PM CDT, and finally exiting eastern portions of South Central Nebraska between 11 PM and midnight CDT. ||The synoptic and mesoscale environment was certainly ripe for a damaging, linear wind event. Earlier in the day, a strong pressure gradient brought hours of sustained 30-40 MPH winds and frequent gusts of 45-55 MPH to South Central Nebraska, as a 994 millibar surface low pressure system organized near the Colorado-Kansas border. Aloft, a powerful, negatively tilted upper level trough centered across the Central and Northern Rockies gradually ejected northeast toward the Northern Plains, allowing considerable large scale forcing and increasing wind fields to overspread Nebraska, including 60-80 knot southwesterly flow at 500 millibars. Lower in the atmosphere, southerly low-level jet winds at 850 millibars increased to around 60 knots. At the surface, a pronounced cold front sliced through the area, providing sharp linear forcing for development of the squall line. Mesoscale severe weather parameters early in the evening included mixed layer CAPE values around 2500 J/kg, and deep-layer vertical wind shear generally 50-70 knots. As the evening wore on, 0-1 kilometer low-level bulk shear ramped up to notably strong values of 40-50 knots, providing a very favorable environment for damaging winds and gustnadoes.

A brief tornado was spotted near Cozad. No damage was reported.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

6 minutes of warning. NWS GID issued a tornado warning for this county at 00:28 UTC, 6 minutes before the tornado touched down, in force until 01:00 UTC.

The county was under a tornado watch, issued at 19:10 UTC and running to 02:00 UTC.

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The Storm Prediction Center had this point in a Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:51 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

Lexington (LXN), 24 km from the path, in the two hours either side.

From the Iowa Environmental Mesonet's archive of airport observations.

The North Platte radar (KLNX), 127 km away, was scanning. The volume nearest the touchdown began at 00:34 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

Local storm reports within 60 km of the path, in the three hours either side.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

The live radar over the trackEvery 2011 tornado in NebraskaEvery tornado in Nebraska since 1950Warnings in force in Nebraska nowThe forecast where you are

15 more were confirmed in the United States that day.

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.