Flash Flood in Ottawa County, Michigan

Three to five inches fell in just one to three hours across portions of central and eastern Ottawa county. This caused extensive flooding of the Grand Valley State University Allendale campus, where over a million dollars worth of damage due to flooding was reported. A coop observer in Allendale measured 4.43 inches of rainfall with this event and a CoCoRaHs observer near Tallmadge measured 3.74 inches of rainfall.

A warm front moved north across southern and central lower Michigan during the day of June 21st, allowing a much warmer and very humid airmass to advect into the area. Thunderstorms developed during the mid afternoon hours due to the building heat and instability and lake breeze convergence. The first of the thunderstorms developed near Holland around 4 p.m. just a couple miles inland of Lake Michigan where the convergence was the strongest. Numerous additional thunderstorms developed in the zone of lake breeze convergence. The storms eventually congealed into a line of storms which marched eastward across the area during the early to mid evening hours.

The storms produced winds of up to around 60 mph in some localized locations. A gust to near 50 mph at the Gerald R Ford Airport in Grand Rapids produced damage to a couple of hangars that injured four people who were in the hangars at the time. The storms also produced some hail, with the biggest hail stones measuring over two inches in diameter in Muskegon and just east of Bangor.

The most significant issue with the storms however was heavy rainfall. A storm that produced very heavy rainfall and did not move very fast in eastern Ottawa county from Allendale to near Marne produced 3 to locally 5 inches of rain within a two hour time frame. This created flooding on parts of the campus of Grand Valley State University, and produced standing water on the roads in Allendale and Tallmadge township in Ottawa county. Some other areas that received the highest rainfall totals were near the intersection of Isabella, Montcalm and Gratiot counties. Western Calhoun county also received significant rainfall and portions of the aforementioned areas saw up to 5 inches of rain falling in a 2 to 3 hour time frame.