This Day in Weather History - August 21

 August 21, 1931 Heat Wave Sends Temperatures to 100F

From the Winnipeg
Tribune Aug 22,
1931, page 1

A week-long heat wave brought temperatures to their peak on August 21, 1931. Winnipeg reached 37.8°C (100°F), tied hottest temperature of the 20th century so far (up to 1931), and the hottest since June 1900 when it reached 38.3°C. 

The heat was preceded by a night of vivid thunderstorms which began just before midnight. Lightning was reportedly spectacular, but the storms produced only a little rain. Localized downpours were, however, enough to provide relief to gardens. The nighttime temperature barely dropped, however, with a low of 20.0°C in Winnipeg. It was said that the storms made it feel more humid. 

From the Winnipeg
Tribune Aug 21, 
1931, page 1