Friday, 11 September 2015

Wet and Humid August

Temperature-wise, August 2015 was pretty much bang on normal with an average mean of 18.5°C. Hot and humid conditions occurred mid and late month with a few cooler periods in between. Overall, rainfall and humidity levels were well above normal for the month.

A heat wave mid month set some records for humidity in particular. 5 consecutive days exceeded 30°C with 4 of those days seeing dewpoints over 20°C and humidex values near or over 40. Three daily high and high minimum dewpoint records were broken during the heat wave. Most spectacular was a dewpoint of 24.5°C on Aug 15, the latest occurrence of dewpoint over 24°C and the 3rd highest daily dewpoint maximum in August since 1953.

Overall, dewpoint in August averaged 13.7°C, tying with 2003 for 14th most moist since 1953. Interestingly, 10 of the last 16 years had an average August dewpoint in the top 20 highest since 1953 while only 2 were in the top 20 lowest.

With high humidity came high rainfall amounts. 107.8 mm of rain fell at Winnipeg airport, the 22nd rainiest August since 1873 and the rainiest since 2010. Higher totals fell in the southern half of the city with locally close to 150 mm.

Rain and severe thunderstorms

There were 6 thunderstorm days at Winnipeg airport, bang on normal. It was a wet and stormy month overall in the Winnipeg area.

Large hail fell over south Winnipeg on August 7 with hail up to golf ball size. Damage to vehicles and gardens occurred. The same storm later produced a tornado near Anola. That same day, another tornado also reportedly touched down southwest of Swan River around midday.

Heavy thunderstorms brought flooding rains on August 22 to Winnipeg. Up to 50 mm fell in less than 1 hour in parts of the south end. Quarter-size hail, wind gusts to 80 km/h and frequent lightning also occurred, making for quite a storm to remember. Numerous streets and underpasses flooded and some were impassable. Water seeped into and flooded parts of St Vital Mall. Lightning also caused a few fires. The daily total rainfall at the Winnipeg airport was 38.4 mm, breaking the old record of 38.1 mm in 1959 for the day. Over 50 mm fell in the south end, making it one of the wettest days since 2010.

In addition, severe nocturnal thunderstorms also occurred during the overnight hours early on August 22. Winnipeg was spared the worst with only minor rainfall amounts and frequent lightning. Cottage country north of the city was not as lucky. A swath of quarter to softball size hail fell from Teulon to Matlock to Beaconia to Pine Falls. Major damage occurred, especially in the Grand Marais to Beaconia region where one person reported that every single vehicle outdoors during the storm was severely damaged. 50+ mm of rain also fell in the area within 1 hour, making for quite a storm. The largest hail reported was a 4-inch diameter hail stone near Powerview.
By Breanna Victoria near Altona Aug 28

Large and damaging nocturnal hailers occurred once again early on August 28, this time southwest of Winnipeg. Toonie-size hail and larger fell from Austin to Ste. Claude to Roseisle to Plum Coulee to Altona. The Plum Coulee to Altona region was hardest hit with hail up to baseball-size. Major damage occurred in Altona with broken windshields and siding, flattened and shredded plants/trees, damaged crops, dented vehicles and took down some small branches. The storm also dumped about 26 mm of rain, causing some street flooding.


  1. That early morning storm on Aug 22 in cottage country will be one I'll never forget. At Hillside beach near Victoria Beach at around 530 in the morning, for about 45 minutes there was not one moment where there wasn't lightning. The most constant flashing lightning I've ever seen! I wish I had a gopro to capture it all as a cell camcorder just wouldn't pick any of it up. A series of storms starting at around 3am rolled off of the lake from the SW. There were on and off storms all day on the 22nd until 11pm that night.

    1. Those nocturnal thunderstorms can be quite amazing! People tend to think the strongest storms occur during the day and don't come to expect such severe storms to pop up early in the morning. I'm not sure why, but no warnings were issued for those early morning storms on Aug 22.