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How we got this spring heat wave

There are a number of words that have been used over the last week or so to try and describe the weather we’ve been experiencing, and I feel pretty much every one has been valid. Words like unprecedented, never before, amazing, unusual, remarkable, unheard of, and even a little scary all describe the weather perfectly. When you go through a seven- to 10-day period where record-warm temperatures are being set at several locations every day, and that most locations set not one or two records but upwards of five to eight records, it is truly some unusual weather!

Let’s try to put things into perspective to show just how strange this weather has been. If we compare our temperatures to the usual temperature range for this time of the year, you would see that things are so warm, our overnight lows are above the high end of the usual high temperature range for this time of the year. Looking back at both Winnipeg’s and Brandon’s temperature records over the past 100 years, we have only seen high temperatures greater than 20 C on three occasions. Table 1 shows some of the all-time March records for both locations.

I guess the biggest question about this remarkable weather is “What caused it?” Three different factors came together to bring about this early-spring heat wave. The first feature was the development of a large summer-like blocking ridge of high pressure over the eastern United States. While this type of pattern can develop at any time of the year, it is much more prevalent in the summer. Usually at this time of the year this ridge would be much weaker and would only last a couple of days, not the 10 or more days that we’ve seen.

This ridge of high pressure brought plenty of sunshine along with very warm temperatures. Across much of the U.S. Midwest, all-time record highs for March have been smashed due to this strong high. This then leads to the second feature: the low snow cover we saw across both the Canadian and U.S. Plains. The low snow cover quickly melted, leaving open fields with little surface water. This means much more of the sun’s energy can go to warm the air instead of melting snow and evaporating water.

The final feature that helped bring the really warm weather over the weekend was a strong area of low pressure that developed to our west. The counter-clockwise rotation around this strong low pulled up plenty of warm air from the southern states, along with extremely high dewpoints. You know things are really weird, weather-wise, when the dewpoint temperatures in the middle of March are in the 14 to 18 C range, which is warmer than the record-high air temperatures!

As with most things in life, it has to come to an end. For us in and around Manitoba that means we’ll leave these unprecedented temperatures and return to those that are just a little unusual. It might seem cold, but we’ll still see temperatures near to above the usual temperature range for this time of the year — although after being spoiled for so long now, it just might be a little hard to take!

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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