Great 1986 Flood in Southeast Michigan

Original : Bill Deedler, Weather Historian, WFO Detroit/Pontiac MI

2016 Edits: Rich Pollman and Danny Costello

September, being somewhat of a transition month between summer and fall, generally brings a taming of the summer heat and thunderstorms. Normal rainfall amounts drop off from the summer maximum and the weather, more often than not, goes into more of a tranquil period before the fall storms begin to rage. But this was not the case on September 10-12th, 1986 in Central Lower Michigan into the "Thumb Region" of Southeast Lower Michigan.

The September 1986 Michigan Flooding was the worst flood disaster in 50 years and would not be exceeded until the August 2014 Metro Detroit Flood. Total damage was estimated between $400 and $500 million, which is between $850 million and $1 billion in 2014 dollars . The August 2014 Metro Detroit Flood would eventually exceed the dollar damage with up to $1.8 billion in flood damage. Of that total, around $120 million ($260 million in 2014 dollars) was crop damage, since the flood came near harvest time. The entire flood area covered generally a 60 mile wide band across the central portion of Lower Michigan. The central axis of the flood area extended from north of Muskegon, near Rothbury, east across all of Central Lower Michigan to near Port Sanilac, in Southeast Lower Michigan's "Thumb Region". Some major cities in Southeast Lower Michigan affected by the flood included Saginaw, Bay City and Midland. It is interesting to note that the city of Flint actually experienced more severe flooding in September 1985 than it did in September 1986.

Several estimates about the likelihood of such a flood like the one in 1986 were tossed about such as a "100 year flood" or a "500 year flood". But to the people of the flood stricken area it is known as "The Flood"! A number of rain events plagued this area through September but the main one occurred September 10-12th, 1986. The flooding rains were triggered by a nearly stationary front which, like the flood area itself, stretched east-west across Central Lower Michigan. Warm, moisture-laden air from the Gulf of Mexico (enhanced by a moisture plume from remnants of a tropical system over the Eastern Pacific), streamed north and east out of the Midwest, across the stationary front into Central Lower Michigan. To the north, cooler, drier air remained entrenched over Upper Michigan. The upper wind pattern across the Great Lakes was conducive in holding the surface front nearly in place, resulting only in a slow drift to the north through the entire period. This in turn, caused any available moisture pushing north across the front to be wrung out and dumped persistently over the same general area.

An extensive area of heavy rain and severe thunderstorms with torrential rains developed just north of the front and extended west from Michigan into Wisconsin. As the moisture from the south overran the front and fell as heavy rain over Central Lower Michigan, it also traversed the same area from west to east during the two day period. This process of precipitation developing and repeatedly moving over the same area is known all too well by meteorologists and hydrologists as "train-echoing". This was the primary mechanism for the persistent heavy rainfall during this particular flood event.

The rain began late Tuesday night, September 9th, over West-Central Lower Michigan and steadily moved east across Central Lower Michigan and into the "Thumb Region" of Southeast Lower Michigan overnight. Rainfall during the September 10-12th period over Central Lower Michigan averaged an incredible 6 to 12 inches, with even isolated reports of up to 14 inches. Much of this deluge fell in a 12 hour period on the 11th. The table below has the rainfall amounts for selected observation points across Southeast Lower Michigan.  The September 1986 rainfall ranks as the wettest month on record for Saginaw, the 3rd wettest month for Flint and the 11th wettest month for Detroit 

The heaviest band of rain over Southeast Lower Michigan for the two day period extended from the Alma area, east across Saginaw into Vassar. As a result of these monsoon-like rains, several rivers surged over their banks and established record heights (see table below).

The Cass River at Vassar with a flood stage of 14 feet rose to an unprecedented (and almost unbelievable) 24.82 feet, or better than 10 feet above flood stage! This level of nearly 25 feet is even more astonishing, when you consider the normal height of the river is about 4.5 feet. Likewise, the Cass River at Frankenmuth rose to around 10 feet above its flood stage with a 27.52 feet reading (flood stage is 17 feet).

Like many locations in and near rivers and drainage areas, the flooding in the town of Vassar was a nightmare! It was definitely one of the hardest hit areas with all the downtown businesses and about 50 homes being flooded. The flood waters reached to the intersection of Main and Huron St. on the northwest side of the Cass River and extended to the intersection of Huron and East St. on the southeast side. The river rose so quickly and forcefully, that some people barely had enough time to get out. Several people awoke in Vassar to find their streets and cars covered in rushing water as the raging river surrounded their homes and businesses. But further downriver on the Cass, at Frankenmuth, vigorous sand bagging on top of permanent levees protected the downtown area from any serious flooding.

Several people lost their lives either directly or indirectly due to the flood. Looking through newspaper articles and related storm reports, at least 10 people died. The body of a hunter was found on the bank of the Muskegon River, a woman who drove her car off a flooded road into the Cass river, two children playing near flooded streams were swept away, two more people drowned while in boats, falling overboard; and another  two men were electrocuted while using sump pumps in flooded rooms. Sadly, the flood also took its toll on human life in another, devastating way. Two farmers, after seeing all their crops under water, committed suicide. Close to 100 people were injured in the flood.

Across Central Lower Michigan, 22 counties were declared disaster areas. This encompassed nearly 14,000 square miles and where 1.8 million people lived.  Even though damage was estimated between $400 to $500 million (1986 dollars), it hard to put a dollar figure on the huge amount of personal items these people lost and also, the emotional scars some still carry with them. To give an idea the volume of water that fell over Saginaw River basin, it was estimated by the state hydrologist (at that time) that if that water could be drained into Lake St. Clair, it would raise its level 10 feet!  The Bay City Times, in retrospect, summed up "The Flood" well by telling their readers to just scan the "D" listings in the dictionary, "It’s all there, Downpours, Drenching, Devastation and Disaster"!

Two key elements that contribute to flash flooding are rainfall intensity and duration. Other factors that play important roles include soil conditions, topography and ground cover. Flash floods cause more deaths each year in the United States than lightning, tornadoes or hurricanes! In the 30 year period ending 2015, averages of 82 people are killed from flooding. Lightning claims 48 lives per year, tornadoes 70, and hurricanes 46.

The National Weather service issues Flash Flood and Flood Warnings when flash flooding or flooding is occurring or imminent. Remember the following when you are in a flood situation...