EF0 tornado, Corydon, Indiana, April 19, 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

April 19, 2011

Touchdown

12:09 AM EDT (04:09 UTC)

Lifted

12:10 AM EDT (04:10 UTC)

On the ground

1 minutes

Path length

0.3 miles (0.5 km)

Path width

50 yards (46 m)

Deaths

0

Injuries

0

County

Harrison County

Touchdown point

38.228, -86.127

Lift-off point

38.230, -86.122

Record number

1104192209-01

Over the space of about four hours from late on April 19 into the early morning hours of April 20, 2011, a squall line brought a historic number of tornadoes to southern Indiana and central Kentucky. Storm surveys over the subsequent few days uncovered 25 tornadoes -the most ever recorded here in one outbreak. On the 19th, low pressure had organized over southeast Kansas with a stationary front reaching east into the central Appalachians. Plentiful moisture streamed northward from the Gulf of Mexico ahead of the system. The Kansas low moved along the front and swung a cold front eastward. Instability, strong upper level winds, and significant changes in wind speed and direction with height helped cause a large squall line to develop ahead of the low and its cold front. The squall line caused severe weather from the eastern Great Lakes to the Red River Valley. Over two dozen tornadoes spun up along the line as it crossed southern Indiana and central Kentucky. Despite the numerous twisters and the fact that they struck during the overnight hours, there were no fatalities or injuries.

An NWS storm survey confirmed an EF-0 tornado with wind speeds estimated at 65 mph. The path length was approximately 0.3 miles with a width of 50 yards. Numerous hardwood and softwood trees were either snapped or uprooted along the northern bank of Indian Creek.

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

35 minutes of warning. NWS LMK issued a tornado warning for this county at 03:34 UTC, 35 minutes before the tornado touched down, in force until 04:15 UTC.

The county was under a tornado watch, issued at 02:15 UTC and running to 07:32 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 Moderate Risk, with a 0.10 chance of a tornado within 25 miles. The outlook in force was issued at 01:10 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.

The Louisville radar (KLVX), 32 km away, was scanning. The volume nearest the touchdown began at 04:08 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 IndianaEvery tornado in Indiana since 1950Warnings in force in Indiana nowThe forecast where you are

69 more were confirmed in the United States that day.

All 70 of them

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.