Fact or Myth: Lake Michigan a Tornado Deterrent

Dark clouds hang over the horizon, tumbling closer as a moist, warm air settles in and lightning strikes in the distance.

Then, the sirens sound.

The wind is picking up and it seems like conditions are getting very dangerous — but with Lake Michigan right next door, there's no way it's a tornado, right?

Wrong.

"That is one of those wives tales that’s been out there for a long time," said Emergency Preparedness Coordinator Tod Pritchard of the Wisconsin Emergency Management department.

Cool lake breezes are not thunderstorms' ideal partner, meaning fewer tornadoes might occur by lakes, but state meteorologist Rusty Kapela said that doesn't mean Lake Michigan air staves off any chance of a tornado.

"The cooler breezes off the Great Lakes ... are what I call low-octane fuel. Thunderstorms like high-octane fuel, which is warm, moist air," Kapela wrote in an e-mail, adding that thunderstorms typically become weaker as they approach or go over Lake Michigan, coming into contact with the "low-octane fuel."  

• Read: More tornado myths and facts available on ReadyWiscons.wi.gov.

"However, in some situations, an atmospheric conveyor belt of warm, moist, unstable air sets up at 4,000 to 6,000 feet above the ground in the form of a low-level jet stream, with winds out of the southwest at 35 to 50 mph," Kapela continue. "When this conveyor belt sets up over southern Wisconsin it doesn't matter whether Lake Michigan is there or not — you're going to have your tornadoes."

It's written in history

This myth was so recently proven false, it might be still be fresh in some Milwaukee-area residents' memories.

On June 30, 2011, Kapela said a storm hit eastern Racine and Kenosha counties with winds of 70 to 90 mph; winds of 50 to 65 mph were recorded in southeast Milwaukee County during the storm.

But the storm actually remained 5 to 10 miles offshore, over Lake Michigan, the entire time, according to the National Weather Service. The strength of the storm over the lake was so strong, however, that it had damaging effects on land — even taking lives.

"Numerous trees were uprooted, power lines were knocked down and roofs had shingle damage," NWS said. "There were reports of felled trees or tree branches damaging homes and mobile homes."

Closer to home, a tornado formed July 18, 1996 in Fredonia, Kapela said. The tornado moved southeast through Ozaukee County and disappeared onto Lake Michigan. That same storm produced a second tornado just a few miles north of Port Washington.

In Wisconsin, the peak tornado season is April to August, according to ReadyWisconsin.wi.gov, but warmer lake temperatures in fall create prime conditions for what are known as "water spouts." 

• Related:

"At this time of the year, the water temperature of Lake Michigan reaches its peak somewhere in the 70-75 degree range ... and leads to an unstable airmass over Lake Michigan in the lowest 5,000 feet of the atmosphere when cold air moves in on northwest or north winds," Kapela said. "There are other non-cold-front cases that involve the winds over Lake Michigan converging from different directions along a line, which results in the formation of rain showers and some waterspouts."

• Photos: A waterspout formed over Lake Michigan on Sept. 24, 2011.

These waterspouts, Kapella said, are not nearly as strong as the water spouts that come from storms — such as the ones that developed in July 1996 after the storms moved offshore.

Know what to do in an emergency

Another "myth" is the idea that the siren warning system found in most communities is meant as an alert to people who are indoors.

It's not.

"It’s an outdoor warning system … people have this belief that they should be able to hear it everywhere throughout the city and their homes," Port Washington Police Capt. Michael Keller said. "Those people in their homes, you’ve gotta believe they’ve got better warning through ... media and technology. There’s no way you can guarantee that something is going to be heard in every building. I think, over time, people have come to believe that that’s what it was meant for, and it really wasn't."

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And though the National Weather Service has the ability to warn areas of severe weather as early as three days in advance — as it did on Feb. 29 this year — that doesn't mean you'll always know when lightning is going to strike.

The Wisconsin Emergency Management website has tips on preparing a plan for emergency weather situations with your family.

The website also has information about weather radios, which the site calls a "smoke detector for severe weather and hazardous conditions."

Weather radios act as an alarm during severe weather situations, and also have a battery backup in case the power is knocked out. They are available at most stores that sell electronics; read more here.