This Day in Weather History - August 17

August 16-17, 1985 Cold Heavy Rainfall Event with 90-140 mm

An unseasonably strong long pressure system moved into the Red River Valley from the United States August 16-17, 1985. The rain moved in late in the day on the 16th, then continued most of the 17th. There were embedded thunderstorms which produced higher rainfall rates. The system brought strong winds along with very chilly temperatures, making it feel much more like fall than summer. The rains were much unwelcomed after an already extremely wet August. Parts of southern Manitoba received over 200 mm of rain during the month from start to finish, making it the wettest on record for many. Winnipeg Airport received 218.0 mm, the wettest August on record since 1872. 

This particular storm system on August 16-17 dumped 50 to 140 mm of rain in the Red River Valley, including in the Winnipeg area. 97.4 mm of rain fell at Winnipeg Airport within a 24-hour period, a new record for the month of August, beating 84.6 mm on August 16, 1884. Some streets flooded as a result of the heavy rain, as well as over 300 basements. Two homes were struck by lightning. The axis of highest amounts was across the western Red River Valley. 

Rainfall amounts August 16-17, 1985

Portage la Prairie City 140.5 mm
Carman 139.6 mm
St Claude 127.0 mm
Portage Southport 121.8 mm
Miami 121.7 mm
Deerwood 117.6 mm
Morden 116.4 mm
Starbuck 110.8 mm
Winnipeg Airport 97.4 mm
Selkirk 95.4 mm
Stonewall 92.8 mm
MacGregor 84.0 mm

Winds gusting over 80 km/h were accompanied by the system as well. Portage la Prairie gusted to 83 km/h, Brandon 80 km/h and Winnipeg 67 km/h. The wind and rain knocked over some power lines, causing outages. Temperatures hovered around 12 to 13°C throughout the day on the 17th, making for an unusually chilly August day. The maximum of 13.8°C was a record low maximum for the date at Winnipeg Airport. 

The cold, windy and rainy weather occurred on a weekend, resulting in various event cancellations. Businesses along the shores of the lakes suffered from lack of business, which had been a theme of the summer. 

From the Winnipeg Free Press, August 18, 1985, page 1

Sources: This post contains info from the Winnipeg Free Press August 18 and 19, 1985, as well as from Environment and Climate Change Canada.