25 years ago, the largest flash flood in Twin Cities history began on July 23, and ended during the early morning hours of July 24. Known locally as the “Superstorm”, the storm caused damage to 9,000 homes and killed two people. Value of the damage was estimated at $27 million. This storm was voted the eighth most significant weather event in the state of Minnesota during the 20th century.
This storm is special to me as It is one of the earliest significant events that I am old enough to remember. I was seven years old at the time, watching my Dad play softball that evening at Dred Scott Playfield in Bloomington. As the game progressed, the skies off to the north and west turned an eerie green, and the outdoor sirens sounded soon after. Play was halted as the participants on the field looked around in confusion at the weather situation. Realizing that conditions were about to get ugly, people bolted for their cars, using any means necessary to exit the park. Upon returning home, seeing images on television of streets turning into rivers, and no one being able to venture out anywhere was something I will never forget. This was my first experience riding out a severe storm locally, and it peaked my curiosity into weather!
During the afternoon hours of July 23, 1987, temperatures were hovering around 90 degrees, with a dew point in the low 70s. This created a very unstable environment for the development of severe thunderstorms and heavy rain as a cold front moving from north to south through the area served as a lifting mechanism. A tornado watch was issued by the National Severe Storms Forecast Center (pre-Storm Prediction Center) for central and southern Minnesota, including the Twin Cities metro, until 9 p.m.
Storms developed west of the Twin Cities during the early evening hours, and moved into the northwestern metro after 6 p.m. Severe thunderstorm warnings were issued at 6:16 p.m. for Wright, Hennepin, and Anoka Counties. Straight-line winds of 70 mph were reported in these areas. The storms went tornadic within the hour as a tornado warning was issued for Hennepin and Anoka Counties at 6:40 p.m., followed by a reported tornado at 6:47 p.m. in Maple Grove. It traveled about five miles into northern sections of Brooklyn Park. It was later rated as an F3 by the National Weather Service with winds estimated at 158 to 206 mph. No fatalities or injuries were reported with this twister. According to Jonathan Yuhas, the twister destroyed 14 homes and damaged over 300 homes and businesses in it’s path. While there were many reports of tornadoes and funnel clouds across the metro throughout the evening, only one confirmed tornado occurred this day.
The severe thunderstorms transitioned into heavy rain producers as they reached the core of the Twin Cities by 8 p.m. The frontal boundary stalled over the southern part of the Twin Cities area, and additional storm cells formed along the front throughout the evening and early morning hours. In a span of six hours, 10 inches of rain fell officially at Minneapolis/St. Paul International Airport (MSP). To this day, it stands as a record for rainfall in a 24 hour period. In addition, the largest official single-day rainfall in Twin Cities history occurred on July 23 as 9.15 inches fell over five hours. During the first three hours, rainfall intensity exceeded 2 inches per hour. Between the 8 and 10 p.m. hour, the rate exceeded 2.5 inches per hour. According to Dr. Mark Seeley, this was a once in a 100 year occurrence. The greatest 60 minute precipitation total during the Superstorm was 2.78 inches.
By sunrise on July 24, parts of Minnetonka, Hopkins, Eden Prairie, Edina, Bloomington, Richfield and south Minneapolis had received about 12 inches of rain. In northeastern Eden Prairie, a weighted water gage recorded 11.32 inches.
Other rainfall totals from across the Twin Cities:
- Edina - 11.09 inches
- Bloomington - 10.36 inches
- St. Paul (Highland Park) – 9 inches
- New Hope – 7.83 inches
- Plymouth – 7 inches
Water was as deep as 13.5 feet on Interstate 494 near East Bush Lake Road in Bloomington, forcing the road to be closed for nearly 5 days until drainage systems could catch up.
Flood damage across the Twin Cities was severe. Just three days before this event, up to nine inches of rain fell over the same areas across the southern metro on July 20 and July 21, setting the stage for flash flooding with any additional rain. Flood waters from the Superstorm closed many roads, and vehicles were completely submerged. Storm sewers could not keep up with the deluge, causing water to gush out of manholes like geysers. Minnehaha Creek and the Nine Mile Creek were turned into raging rivers, threatening residences and roads along it’s banks. One person died in Hopkins when his vehicle was swept into Nine Mile Creek. Thousands of basements were flooded, and some roofs collapsed. A man in south Minneapolis was killed in his basement when a foundation wall collapsed on him. Water entered businesses along flooded roadways, and the ground level of the Southdale Center in Edina was covered with one to three inches of standing water. Some stores sustained water damage. Stranded shoppers stayed overnight inside the mall.
The two heavy rain events during the month (July 20-21 and July 23-24) combined to give the Twin Cities it’s wettest summer on record, with 23.52 inches of rain falling from June to August. Total annual precipitation in 1987 was 32.16 inches. Of that total, nearly 56 percent of that fell in July, and 31 percent of the precipitation that year occurred during the Superstorm.
- Minnesota State Climatology Office
- KARE News11 Sunrise, July 24, 1987. Video provided by TC Media Now.
- KARE News11 at 5, July 24, 1987. Video provided by TC Media Now.
- WCCO-AM Radio storm coverage (MP3 format): Part 1, Part 2, Part 3. Audio provided by RadioTapes.com. (Note: The large audio file size make take a few moments to load).