Dexter Tornado of March 15, 2012 northwest of Ann Arbor Michigan

The Storm Prediction Center issued mesoscale discussion #258 at 3:52 EDT with the expectation primarily of hail. At 4:30 pm Severe Thunderstorm Watch #76 was issued, effective immediately, with standard boilerplate language that severe thunderstorms occasionally can and do produce tornadoes. Conditions were marginal and it wasn't until 5:44 that mesoscale discussion #260 mentioning isolated tornadoes was issued.

Images courtesy NOAA Storm Prediction Center.

Meanwhile the Detroit NWS was watching storms grow rapidly as they moved slowly eastward into Livingston and Washtenaw counties, and when strong rotation was noted by radar, the first tornado warning was issued just after 5:00 as shown below. While the storms had been moving east or even slightly north of east, it soon became evident this storm was moving southeast, as shown by the tornado track below. The tornado touched down at 5:17 EDT. The southeast movement fortunately meant it would pass west and south of Ann Arbor (where it's not clear how seriously U of M students and U of M bus drivers took the warning sirens), and instead (as two subsequently issued tornado warnings showed) head toward Saline and Milan (where most residents have more common sense; editor's disclaimer- the author is a Purdue graduate). The radar loops below courtesy of the Weather Underground (an admittedly nice offshoot of U of M) show the southeastward movement, and the hook echo associated with the slow-moving tornado that moved through Dexter between 5:17 and 5:52 (note the image at 17:16), and a second hook that developed or re-developed after the storm moved south of Interstate 94 (note the image at 18:16 an hour later), although that funnel did not appear to reach the ground .

Hudson Mills Park video
Dexter tornado forming
image courtesy National Weather Service click images above for youtube videos

 

Tornado Path
image above courtesy National Weather Service Detroit office

 

 
animated images courtesy Weather Underground (a very useful offshoot of U of M)

 

screenshot taken from Weather Underground

 

WXYZ Channel 7 Action News video myfoxdetroit WJBK Fox 2 Photo Gallery

 

ABC News Video

 

March 15th storm reports from SPC