Exceptional heat yesterday in southern Manitoba

An intense heat wave has gripped southern Manitoba for the last few days, and will continue today with high temperatures once again in the mid thirties. 

The peak of the heat during this heat wave occurred yesterday with temperatures not seen in decades in southern parts of the Manitoba Red River Valley. Temperatures reached over 40°C in these parts, the first time that has occurred in southern Manitoba since August 2018 when Elm Creek and Waskada hit 40.0°C. The high of 41.3°C in Gretna yesterday was the highest recorded in Manitoba since August 6, 1988 when Starbuck reached 41.5°C, the same day that Winnipeg had reached a record high of 38.7°C. In addition, it was higher than ever recorded anywhere else in Canada this early in the season (via Thierry Goose). The only other time it got this hot this early in the season was in the same area of Manitoba on May 30, 1934 when Morden hit 42.2°C. 

It would appear the southern Red River Valley of Manitoba is the only spot in Canada that can get this hot this time of year. A few factors result in this possibility, such as the Manitoba escarpment which produces a downsloping effect when winds are from the southwest. The Red River Valley also has the lowest elevations of the southern Prairies. In dry years such as this one, the soils are also still quite dark with very little in the way of evapotranspiration, resulting in strong absorption of sunlight. 

The following table shows the highs over 40°C that were recorded yesterday in southern Manitoba (note that Winkler MAFRI station also later recorded 40.6°C - data went missing but they later retrieved it back).

In Emerson, it was the first 40°C recorded since 1939 (via Scott Kehler). In Morden, it was the first since 1989 and only the second time 40°C was reached in June (the other occurrence was 40.6°C on June 18, 1933). 

More communities in southern Manitoba, including Winnipeg, could have hit 40°C if it wasn't for a cold front which quickly moved through in the afternoon. In Winnipeg, if a high of 40°C had occurred, it would have been the first since 1949. Instead, the official high was 36.5°C, breaking the daily record of 35.6°C in 1988. It was only the fourth year since 1872 to have recorded temperatures over 36°C this early in the season (the others being in May 1964, 1980 and 1934). Temperatures over 37°C were also recorded at some backyard sites such as 37.2°C in Charleswood and 37.6°C in Whyte Ridge. 

South of the border, it was just as hot in North Dakota. Grand Forks reached over 39°C, the hottest temperature recorded since the late 1980s when temperatures over 40°C occurred (via NWS Grand Forks). More than half of North Dakota exceeded 37°C, with several locations reaching close to or above 40°C (via Daryl Ritchison). 

Also of note, the temperatures rose incredibly fast in the morning hours, typical of very dry and sunny days such as in the deserts. Winnipeg Airport recorded its hottest 9am, 10am and 11am temperatures on record since 1953, and its second hottest noon temperature, as seen in the following table:

Note that on July 11, 1936, it is estimated that the temperatures in the morning were very similar to yesterday (via Rob Paola). That day in 1936 hit 42°C, which goes to show how hot it could have been if the cold front did not come through yesterday afternoon. 

Other parts of southern Manitoba rose even quicker than Winnipeg. By 9am, it was already 31°C in Carman and Winkler. In the same communities, it was 34°C by 10 am. By 11 am, it was 36°C from Morden to St Adolphe. By noon, it was 38°C in Morris, Morden and Winkler. 

The afternoon cold front unfortunately advanced too quickly for Winnipeg to receive any thunderstorm activity. Thunderstorms developed quickly along and just south of the US Border in the late afternoon and early evening hours along the front, then moved southward. Intially, it was difficult for much rainfall to reach the surface due to the deep dry and hot layer between the surface and the clouds. These types of conditions tend to produce strong wind gusts with thunderstorms due to significant evaporation of rainfall as it falls from the clouds. Evaporation requires drawing energy from the air, thus cooling the air and further accelerating the descending air under the thunderstorm because cold air is heavier than warm air. With the storms yesterday, several gusts between 80 and 85 km/h were recorded south of the border (via Daryl Ritchison). In addition, a gust of 95 km/h was recorded at the Menisino Manitoba Agriculture station in southeastern Manitoba. This particular gust in Manitoba occurred as the storms had just developed, with no rainfall accumulation recorded (dry microburst). The strong winds and initial lack of rain reaching the ground had resulted in blowing dust south of the border. 

Blowing dust from developing thunderstorm at Maddock ND NDAWN station (via Daryl Ritchison)

Due to the heat wave, the province of Manitoba announced that it would allow the reopening of splash pads and pools to allow residents without air conditioning to cool off. Libraries and community centres could also open as cooling centres for the vulnerable. These were announced due to the ongoing COVID-19 pandemic which has resulted in numerous closures of public spaces. In addition, restrictions on backcountry travel and burning permits were announced to help prevent fires during the exceptional drought situation. 

US Drought Monitor showing exceptional drought in ND extending into MB, the worst drought category