On July 2, 1997 Lower Michigan experienced a severe weather outbreak that produced 16 tornadoes, the most ever for a single event for the state of Michigan* at that time (19 tornadoes occurred in Michigan on May 21, 2001*). In Southeast Michigan there were 13 tornadoes (the most ever for Southeast Michigan in a single episode*). The tornadoes occurred in Saginaw, Genesee, Lapeer, Livingston, Oakland, Macomb, and Wayne counties (Image1 Image2). In addition, the thunderstorms produced straight line winds (winds not associated with tornadoes) of up to 100 mph, which also caused extensive damage. Unfortunately, 7 lives were lost directly from the storms along with a number of other indirect storm related deaths. Damage estimates from the storms were over 135 million dollars (1997 dollars, 168 million dollars adjusted to inflation, 2006).
*Prior to 1994 tornadoes were classified as a distinct tornado if there was a 5 miles break between damage paths. After 1994, this standard was change to 2 miles between damage paths. Had the 5 mile rule been in place, the number of tornadoes in Southeast Michigan during the July 2, 1997 Outbreak would have been between 7 and 13.
Also of note, the tornado intensity in 1997 was based on the Fujita or F Scale. On February 1, 2007, the NWS started rating tornadoes based on the Enhance Fujita or EF Scale.
An unusually strong storm system for July moved through the Great Lakes region on that day. This storm system not only featured a strong cold front, but also a strong storm in the mid levels of the atmosphere which provided additional energy . An upper level band of strong winds (the jet stream) was also unusually strong for July and positioned over the Great Lakes region. Combine all of this with a very warm and humid air mass, and the atmosphere was set up for severe thunderstorms (12Z DTX sounding).
The wind profile of the atmosphere was favorable for the development of supercell type thunderstorms, the most dangerous type of thunderstorm. Supercell thunderstorms are the most likely type of thunderstorms to produce a tornado, and most of the strong and violent tornadoes are produced from supercell thunderstorms. The wind profile that favors supercells is where there is strong wind shear. This can be accounted in two ways, and increase in wind speed with height or a clockwise turning of the wind direction with height. On July 2nd, the atmosphere had both types of wind shear over Lower Michigan ( VAD wind profile Hodograph Storm Relative Helicity).
The National Weather Service in White Lake issued a Severe Weather Potential Statement for Southeast Michigan at 520 a.m. and then an update at 1135 a.m. on July 2nd. Both of the Statements mentioned the possibility of a widespread severe weather outbreak with isolated tornadoes. A tornado watch was issued by the Storm Prediction Center at 110 p.m. that covered most of the Lower Peninsula, as a line of storms began to develop along the cold front in far western lower Michigan. The first warning that was issued by the National Weather Service in White Lake, was a tornado warning for Saginaw county at 305 p.m. The last tornado warning was issued for Wayne county at 701 p.m.
There were three supercell storms that moved through Southeast Michigan that produced the tornadoes. The first supercell moved from southern Saginaw County through Genesee and Lapeer Counties and then weakened as it moved into St. Clair County. The second supercell moved from Livingston County through Oakland County and then into Macomb County. The third cell moved along the Livingston and Washtenaw Counties. border and then into Wayne County ( Radar Loop Satellite Loop ).
The supercell that moved through Saginaw and Genesee Counties and then into Lapeer County spawned 9 of the 13 tornadoes. At 3:41 p.m., there was a brief tornado on the southwest side of Chesaning and then at 3:46 pm in the small community of Oakley. By 4:10 p.m. another tornado produced damage near Layton Corners. At 4:06 p.m., the National Weather Service Doppler Radar at White Lake, Michigan depicted that supercell (Figure 2a). The storm relative velocity product (Figure 2b) at the same time showed a Tornadic Vortex Signiture (TVS), with a rotational velocity of greater than 45 knots, just exiting the Chesaning area. On radar velocity products, red indicates where precipitation is moving away from the radar beam, and green indicates where precipitation is moving toward the radar beam. When these areas of red and green get close to each other and cyclonic rotation is observed, it is called a mesocyclone, a sign of a severe storm. As this rotation gets tighter and closer to the ground, tornadic signatures may begin to develop.
This supercell continued its east-southeast movement and tornadoes were confirmed near Burt, Montrose, and 2.5 miles south of Montrose. These tornadoes all occurred at about 4:20 pm. The supercell continued to show strong rotational signatures that were increasing when the storm produced an F3 tornado near Clio at 4:30 p.m. As the storm moved to the east over Thetford township, just 5 miles east of Clio, the radar indicated rotational velocity of greater that 55 knots with a diameter of only .7 nautical miles at 4:41 p.m. (Figure 3) and greater than 50 knots with a diameter of .5 nautical miles at 4:46 p.m. (Figure 4). At 4:45 p.m. another F3 tornado was produced by this supercell over Thetford Township, were one person was killed. The last tornado that was spawned by the supercell occurred at 5:15 p.m. 4 miles northeast of Columbiaville in Lapeer County.
The second supercell entered the NWS White Lake County Warning Area (CWA) of Responsibility by dropping a tornado northwest of Fowlerville in Livingston County. At 4:41 p.m., the Doppler radar reflectivity ( Figure 5) indicated a supercell to the north of Fowlerville and another cell to the southwest of the community. It was the supercell to the north of Fowlerville that produced the Livingston County tornado. This tornado stayed on the ground for approximately 10 miles, the longest track of any of the tornadoes on July 2nd. The supercell then moved into northwest Oakland County where another tornado was produced 3 miles northeast of Holly at 5:32 p.m. Unfortunately, one person was killed from this tornado. The last tornado that was spawned by this supercell occurred south-southeast of Romeo. The radar at 6:16 p.m. showed a classic hook echo ( Figure 6a Figure 6b) and strong rotation.
The last of the tornado bearing storms moved through Wayne County. In the 6:16 p.m. reflectivity image ( Figure 7a), notice the line of thunderstorms from Lake St. Clair to Royal Oak. Then there is a wave in the line that extends from Royal Oak to Detroit and Dearborn. This is called a Line Echo Wave Pattern (LEWP). Within the wave is another common place for tornadoes to form. South of this feature is a bow echo which is usually associated with strong straight line winds. In the storm relative velocity product (Figure 7b) there is greater than 55 knots of rotation just west of I-75 in the city of Detroit. From 6:00 p.m. to about 6:10 p.m. there was a strong F2 tornado that was on the ground for 5 miles across Northwest Detroit, Highland Park, and Hamtramck. As the bow echo moved through the Grosse Pointe areas, the 6:26 p.m. base velocity data from the radar indicated greater that 64 knots (74 mph), and up to 100 knots (up to 115 mph) of potential "straight line" wind (Figure 8). Five people were killed and eight others were injured in Grosse Pointe Park as these strong winds moved through the area.
Storm Data and Surveys
|Southeast Michigan Data||State of Michigan Data|
|Damage south of Clio, F3 tornado
||Thetford Township, F3 tornado
||Thetford Township, F3 tornado
|Thetford Township, Vassar Road
|Oakland County, I-75 at Holly Road
Damage from 100+ mph straight line wind
just before tornado touchdown
Severe Weather Potential Statements
A Listing of the Warnings that were issued by NWS White Lake, Michigan