EF0 tornado, Knoke, Iowa, July 3, 2007

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

July 3, 2007

Touchdown

9:05 PM CDT (02:05 UTC)

Path length

0.1 miles (0.2 km)

Path width

30 yards (27 m)

Deaths

0

Injuries

0

Crop damage

$1,000

County

Calhoun County

Touchdown point

42.510, -94.790

Lift-off point

42.510, -94.790

Record number

0707032005-01

A cold front moved southeast across the Dakotas into northwest Iowa during the late afternoon and evening hours. The airmass became quite unstable ahead of the cold front with high temperatures reaching near 90 F. and dew points around 70. CAPE values were around 4000 J/kg by the late afternoon as lifted indices fell to around -9. There was a decent amount of CAPE available in the -10 to -30 C. layer of the atmosphere. I spite of this, very little hail was realized with the freezing level around 16,000 ft. Shear was fairly weak during the day and increased to around 30 kts during the evening hours. A narrow line of thunderstorms developed in northwest Iowa during the early evening hours, then drifted south-southeast into west central and central Iowa during the night. One of the storms produced a brief spin-up tornado in Calhoun County west of Jolley. The LCL level was relatively high in the area, at around 1500 meters. That may have limited the lift of the tornado. It touched down in a field and caused little damage. Many of the storms produced gusty winds and for a brief period of time the line produced severe winds as they moved into an area of higher DCAPE air with values in the 800 to 1000 J/kg range. There were scattered reports of crop damage and downed trees as the storms passed. During the late evening, an area of severe thunderstorms to the northeast of the DMX CWA back developed into northeast Iowa. One of the storms produced Nickel size hail southeast of Waterloo.

Tornado touched down briefly in a field northwest of Jolley.

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

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.

The county was under a tornado watch, issued at 21:06 UTC and running to 03:38 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 00:55 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 Des Moines radar (KDMX), 123 km away, was scanning. The volume nearest the touchdown began at 02:04 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 2007 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

13 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.