Michigan Tornado History: 20th Anniversary of the March 27, 1991, Tornado Outbreak
Today marks the 20th Anniversary of the March 27, 1991, tornado outbreak, one of the largest in Michigan history. Fifteen tornadoes touched down across the state, including 4 F3, 3 F2, 3 F1, and 5 F0 tornadoes. These tornadoes resulted in 18 injuries and over 40 million dollars in damage.
March 27, 1991, in Michigan was characterized by unseasonably warm and humid conditions, with several rounds of rain and thunderstorms. A warm front had passed northward through the Lower Peninsula of Michigan by 7am, placing Michigan in southerly flow, allowing temperatures to reach into the mid-60s by the afternoon, with dew points approaching 60 degrees, from the Ohio border to the Straits of Mackinac.
An occluding surface low pressure was located over north-central Kansas the morning of March 27, 1991, with scattered thunderstorms along and ahead of the cold front.
At 500mb, a significant trough located over the Central Plains would work its way northeast as a cutoff low over central California began to open up and translate into the Four Corners region. A closed low at 850mb with a 65 knot low level jet was located over the Western Great Lakes and Middle Mississippi Valley. There was a split flow in the jet stream, with a 100 knot jet streak.
As the day progressed, strong southerly winds in advance of the storm system helped to increase temperatures and moisture across the Lower Peninsula. By late afternoon, temperatures across the Lower Peninsula had reached the mid- to upper-60s, and dew point temperatures were in the mid- to upper-50s, despited several rounds of rain and thunderstorms. Reported cloud bases were between 2000 and 3000 feet.
The afternoon sounding from KFNT showed an unstable atmosphere, with in excess of 1000 J/kg of cape, and a cyclonically curved hodograph. This instability and shear was more than sufficient for severe thunderstorms and supercells.
The first tornadoes touched down at 4:02pm in Northern Lower Michigan, with the last of 15 tornadoes touching down at 9:53pm in St. Clair County.