The Evansville tornado had winds of up to 135 mph and was classified as an F2. Here's what that means.

Alex Groth, Milwaukee Journal Sentinel
Updated ·3 min read

The National Weather Service assessed the strength of a tornado after it touched down in Wisconsin on Thursday just south of Madison between Evansville and Edgerton.

An EF-1 occurred about 5:15 p.m. near Albany, just southwest of Evansville, then an EF-2 tornado touched down at about 5:40 p.m. that moved northeast from Evansville to southwest Jefferson County. Winds reached up to 135 mph in the Evansville tornado.

Tornadoes can occur in many different shapes and sizes—from a few yards to over one mile wide. They can move slowly or at speeds of 60 mph or faster.

Tornadoes can change intensity quickly, so all tornadoes should be considered dangerous no matter the level. Here's what to know about how tornadoes are classified and the danger signs:

How are tornadoes classified?

Tornadoes are classified using what's known as the EF scale, which factors in estimated wind speeds and related damage.

  • EF-0: wind speeds 65 to 85 mph

  • EF-1: wind speeds 86 to 110 mph

  • EF-2: wind speeds 111 to 135 mph

  • EF-3: wind speeds 136 to 165 mph

  • EF-4: wind speeds 166 to 200 mph

  • EF-5: wind speeds greater than 200 mph

What are tornado danger signs?

  • Dark, greenish clouds and sky

  • An isolated lowering of the the base of a cloud during a thunderstorm, also known as a wall cloud

  • Debris cloud

  • Large hail

  • Funnel cloud

  • Roaring noise

What was the worst tornado to hit Wisconsin?

Wisconsin started keeping official track of tornadoes in 1950. According to those records, the deadliest tornado was an EF-5 that hit Colfax on June 4, 1958. The twister was part of an intense outbreak that affected a large part of the upper Midwest from June 3-5, 1958. It spawned four severe tornadoes across the Eau Claire–Chippewa Falls metropolitan area, primarily along and near the Chippewa and Eau Claire rivers. The 90-mile tornado left 29 dead and injured more than 200.

In 2005, 62 tornadoes hit Wisconsin, which remains the record for the most tornadoes in a single year from the last 30 years. In comparison, 1952 only saw one tornado the whole year. According to the National Weather Service, the average Wisconsin tornado is an EF-1, lasts about 9.8 minutes, has a path length of 5.5 miles and a maximum width of 121 yards. On average, June sees the most tornadoes, but the season lasts from April to September.

How to prepare for a tornado:

The National Weather Service recommends the following safety tips to prepare for a tornado:

  • Make sure you know which county you live in. The National Weather Service issues tornado warnings that could include an entire county, or portions of neighboring counties

  • View the latest forecast via the National Weather Service, TV or news station

  • Know your communities warning system. Communities have different ways of warning residents about tornadoes, with many having sirens for only outdoor warning purposes

  • Designate a safe room in your home where your family and pets can stay during a tornado. This could include a basement, storm cellar, or an interior room on the lowest floor with no windows

  • Practice periodic tornado drills so everyone knows what to do during a tornado

  • Prepare for high winds by removing diseased and damaged limbs from trees. Secure any lawn furniture, trash cans and hanging plants

For more information, visit ready.gov/tornadoes.

Ridah Syed contributed to this report.

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This article originally appeared on Milwaukee Journal Sentinel: Has Wisconsin ever had an EF5 tornado?