Note: Click the "fullscreen" button under the photo captions to view the graphics at a larger size.
When we look at where all of the tornadoes have traveled in Michigan, there appears to be three main "tornado alleys."
The maps show all of the recorded tornadoes in Michigan since 1950, according to the Storm Prediction Center.
If you look at the maps of tornado tracks, there are areas that have had more tornadoes than surrounding areas. These areas where more tornadoes have occurred would be what I call Michigan's "tornado alleys."
There are three common paths of tornadoes, as I see it. The largest tornado alley is a wide swath from west to east from the Grand Rapids area to the Lansing area to the Flint/Saginaw area. The second tornado alley lies in far southern Lower Michigan from the Coldwater area to Hillsdale to Adrian to Monroe. There appears to be lesser amounts of tornadoes between those two tornado alleys, helping the concentrated paths of tornadoes stick out.
The final tornado alley is an interesting one, and not where you would expect it. Look at northeast Lower Michigan. There is a group of stronger tornadoes from the Gladwin area through West Branch to Hale to Oscoda and Harrisville.
The Upper Peninsula hasn't had enough tornadoes since 1950 to visually pick out a tornado alley there.
Here's a database of all the tornadoes since 1950. You can choose a county, year, tornado strength or all of the above.
I think in each of these broad perspective tornado alleys there are concentrated areas making even more localized tornado alleys. It will be interesting to look at those localized tornado alleys in further posts.
What would cause Michigan's tornado alleys?
When I look at these tornado alleys, I see a combination of two geographic situations as the likely cause. Of course we know the Great Lakes affect our weather, and our tornado tracks are no exception. Tornadoes usually need large amounts of low-level wind shear. This means the wind direction changes a lot in the lowest 6,000 feet of the atmosphere. Wind shear is the number one factor that takes a severe thunderstorm and turns it tornadic.
That's where the Great Lakes fit in. The northeast tornado alley and the wide Grand Rapids to Flint/Saginaw tornado alley often have a lake breeze somewhere during tornado development. The lake breeze drastically changes the wind direction at the surface, and produces large amounts of wind shear. This lake breeze effect is real apparent in the northeast Lower tornado alley. The lake breeze there will move in off Lake Huron, producing an easterly wind. A severe thunderstorm moving into northeast Lower from the west hits the lake breeze. The storm then has enough wind shear to produce a tornado. The same effect happens in Saginaw and Genesee Counties with lake breezes and northeast winds coming off the Thumb. West Michigan can have the opposite wind with lake breezes from Lake Michigan.
The other factor is probably just the lay of the land. Possibly the hilly areas of southern Lower Michigan do something to alter the wind-flow pattern. This may give storms increased wind shear and a better shot at producing a tornado.
Related: Amazing drone views of Michigan tornado wreckage
What are your thoughts?
Have you observed particular paths of tornadoes in your area? Do you have any thoughts why? Please post your comments below.
MLive Chief Meteorologist Mark Torregrossa has been forecasting Michigan weather for more than 25 years. He's been chief meteorologist at three television news stations in Michigan, and he's an avid gardener and hunter. Email him at mtorregr@mlive.com and find him on Facebook at facebook.com/mark.torregrossa and Twitter @weathermanmark