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.

Warm and Very Humid July

July 2015 was perfect for spending time outdoors and enjoying the many activities we look foreward to in the summer. Generally, temperatures were close to or slightly above seasonal on most days, but consistently high humidity made it feel hotter. This high humidity helped fuel an active month for thunderstorms and heavy rains across southern Manitoba.

The average mean temperature at Winnipeg airport was 20.2°C in July, slightly above normal (+0.6°C) and the warmest since 2012. Despite being above normal, only 2 days exceeded 30°C at Winnipeg airport. The 1981-2010 normal is 5 days. In fact, the first 30°C day of the year wasn't until July 26, the second latest on record since 1872.

Top 5 latest dates to reach 30°C for the first time in a year
1. Aug 16 (2008)
2. Jul 26 (2015)
3. Jul 24 (1882, 1927)
5. Jul 19 (1920)

The lack of 30°C days at the airport was a little surprising and masked the fact that it was a hot July. Most locations around the city were hotter. Charleswood recorded 10 days over 30°C.

The humidity was the main story of July. 14 days saw a dewpoint over 20°C at Winnipeg airport, tying with 1957 for the most in July since 1953. The 1981-2010 normal is 6 days. In addition, the average hourly dewpoint observation was 16.1°C, the second highest in July since 1953. The 1981-2010 normal is 14.2°C.

Top 5 most humid Julys since 1953 (according to average hourly dewpoint observation)
1. 16.5°C (2012)
2. 16.1°C (2015)
3. 15.5°C (1966, 1989)
5. 15.4°C (1955, 1983, 2007, 2010)

Top 6 most 20°C dewpoint days in July since 1953
1. 14 days (1957, 2015)
3. 12 days (1955, 2001, 2005)
6. 11 days (1966)

The dewpoint peaked at 24.1°C on July 12, breaking the old record of 23.9°C in 1955 for the day. This occurred during an 8-day streak with maximum dewpoints over 20°C. Two other maximum dewpoint records were broken during the month (22.5°C on July 27 and 22.4°C on July 28).

Dark as night during a t-storm near 7 pm July 4 in Wpg

Thunderstorms were also a big story in July with 8 thunderstorm days at Winnipeg airport, the most in July since 2005 and the most for any month since June 2007. The worst of the storms missed Winnipeg however. Rainfall was slightly below normal for the month as a result. Many parts of southern Manitoba got over 100 mm of rain in July, including 178 mm in Portage la Prairie. Even isolated portions of southwest Winnipeg got a little over 100 mm. Some of the heaviest rains were in the Morris to St. Pierre Jolys area where over 200 mm fell.

Another memorable event was the July 27 southwestern Manitoba tornado event. Full summary of the event is on A Weather Moment.