A historical look at May’s warmth and summer heat

Upper lows we’ve seen so far this year haven’t tapped into as much cold weather

I guess the first thing I need to update is the precipitation totals for May, as the expected late-May/early-June storm system brought some significant rainfall totals across our region. The Winnipeg region ended up coming in about 15 mm above average and the Brandon region came in right around average, while the region around Dauphin was about 10 mm below average. This means May ended up having near- to slightly above-average amounts of precipitation.

The next topic has to do with these pesky upper lows that have been hitting every couple of weeks for the last month now. If you remember back a couple of years, we saw several of these upper lows over the late spring and early summer that brought plenty of cold weather and rainfall. So far this year these upper lows haven’t been as strong and haven’t been able to tap into as much cold weather. This fact still leads me to believe we’ll end up seeing a warmer-than-average summer, since so far, even with the upper lows, we are still seeing temperatures running near to above average.

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A few people have asked me just what kind of temperatures we would see if we have a hot or even record-hot summer. It can be tough to pick out just what makes a hot summer. You can have really hot days, but cooler nights, or pretty warm days and very warm nights. The best way to measure overall temperature is to use the mean or average temperature for the whole summer, which for this we’ll use July and August. In the table you’ll see the top five hottest summers, looking all the way back to the 1880s.

Winnipeg’s hottest summers (average temperature in degrees celcius)

  • 1983 – 22.3
  • 1936 – 21.7
  • 1955 – 21.5
  • 1930 – 21.2
  • 1989 – 20.8

If we look at the summer of 1983 a little closer, starting with July and using Winnipeg’s data, there were nearly 15 days during the month with daytime highs greater than 30 C. While there were a lot of warm days, the hottest day was only around 34 C. Overnight lows were mostly in the 14 to 17 C range, with a couple of days only dropping down into the low 20s. There were a couple of cool days at the start of the month, with an overnight low on July 5 dropping down to 5 C. The heat was turned up even more in August 1983, with 17 days having highs in the 30s and a couple of days peaking in the 36 to 37 C range. Overnight lows were a little cooler than they were in July, with most nights falling into the 12 to 16 C range. July’s precipitation was very light, with amounts only in the 20-30 mm range. Thunderstorms in August pushed precipitation values up to around average for the month, with about 80 mm reported.

Another topic I have been asked about concerns the statement I made about the last time we saw a May that was as warm as it was this year. Basically, it seems a few people didn’t believe me, so I figured I would take a bit of a deeper look into May temperature records just to help clarify things a little bit. All three of our main locations recorded a mean monthly temperature about 2.5 C above average for May, which is a mean temperature of between 13 and 14 C.

Looking back at Winnipeg’s data, the last year that we saw a mean temperature that was in this range was in 1991, when the mean May temperature was 14.6 C. In Brandon you would also have to go back to 1991, when the mean monthly temperature hit 13.1 C. For Dauphin we need to go back to 1989, when the mean monthly temperature hit 13.1 C. I created a graph showing the mean monthly May temperatures for Winnipeg dating back to 1939 that will help you see just how long a streak of average to below-average May temperatures we have experienced. The blue line on the graph is the long-term average for the month of May. Looking at the graph, you have to go back to the 1980s to see an extended time frame that had warmer-than-average Mays. That means you would have to now be in your late 20s or early 30s to remember this type of May weather. Kind of remarkable, when you think about it.

About the author

Co-operator contributor

Daniel Bezte

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.



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