EF0 tornado, Forest Lake to Scandia, Minnesota, July 17, 2010

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 17, 2010

Touchdown

8:44 PM CDT (01:44 UTC)

Lifted

8:52 PM CDT (01:52 UTC)

On the ground

8 minutes

Path length

5.2 miles (8.3 km)

Path width

50 yards (46 m)

Deaths

0

Injuries

0

Property damage

$50,000

County

Washington County

Touchdown point

45.238, -92.959

Lift-off point

45.276, -92.868

Record number

1007171944-01

The atmosphere became very unstable Saturday afternoon, and along with a strong wind shear, aided in the development of very large hail, isolated tornadoes and significant straight-line wind damage. ||The first storm developed near Alexandria and moved southeast along Interstate 94 before dying in the southwest part of the Twin Cities late that afternoon. Numerous reports of very large hail, up to the size of softballs, occurred near St. Cloud, southeast to Watertown. ||The next area of severe storms developed across central Minnesota, and far west-central Minnesota and moved east and southeast toward east-central Minnesota where a strong bow echo developed and moved across the northern portion of the Twin Cities Metropolitan Area. ||There was widespread damage along the leading edge of this bow echo where numerous trees, power lines and homes were either uprooted, blown down, or destroyed. ||These storms moved into west-central Wisconsin and also caused damage to trees before weakening toward the late evening.

Hundreds of trees were broken or toppled, including some that fell on sheds and houses. Shingles and soffits were removed from some houses.

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

34 minutes of warning. NWS MPX issued a tornado warning for this county at 01:10 UTC, 34 minutes before the tornado touched down, in force until 01:45 UTC.

The county was under a tornado watch, issued at 20:17 UTC and running to 04:00 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 Moderate Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 00:54 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 Minneapolis radar (KMPX), 68 km away, was scanning. The volume nearest the touchdown began at 01:42 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 2010 tornado in MinnesotaEvery tornado in Minnesota since 1950Warnings in force in Minnesota nowThe forecast where you are

6 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.