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What’s Up With May’s Weather?

After a week of really nice weather across much of agricultural Manitoba, we saw the weather turn back to cool, wet conditions. Some of the comments I’ve been hearing about the weather are that our seasons are off by a month, or simply that Mays appear to be getting wetter and colder. At first I kind of dismissed these comments, but then I started to think back to when I was younger and it does seem that the nice, warm, dry Mays of my youth just don’t happen anymore.

So I decided to do a quick check back at the weather data for both Winnipeg and Brandon to see if there is any truth to this idea that our Mays are getting colder and wetter. The first thing I noticed is that, while the temperatures and precipitation amounts between the two centres were understandably different, the pattern and trends between them were identical. So I chose just to include one city’s set of graphics.

I took the mean monthly temperatures and precipitation totals from 1980 to 2009 and graphed them out. When I did this, I didn’t notice a real obvious trend in the data. So I then took that same data set and averaged out the monthly temperatures for each decade of data. I then graphed this data out and if you take a look at the two graphs I have included, you can see there is a rather interesting pattern.

If we look at the first graph showing the mean decadal temperatures, you will see that first of all, there is not a huge difference in temperatures between the decades, and considering that this graph is an average of 10 years of data, this makes sense. If we look at the temperatures during April there does not appear to be any pattern. The 1980s were warm and so were the last 10 years. Meanwhile, the 1990s were a cooler decade. If we jump ahead and look at June, we again do not see any real pattern. This time it was the 1990s that were a little warmer.


Now, if we look at the month of May, there does appear to be a pattern emerging, and that pattern seems to confirm what most people have been noticing. May does seem to be trending towards colder conditions.

I did the same thing with precipitation data, and interestingly enough, the same general patterns emerged. April and June showed what we would expect: random variability. May, on the other hand, showed a definite trend toward wetter conditions.

I wasn’t content with just leaving it at this, knowing that a particularly unusual year could bias the data during any decade to give a false indication of what that decade was like – so I went back to the data and removed the lowest and highest readings for both temperature and precipitation. After I did this the result for all three months did not change, which showed me that the data was not being biased by any particularly unusual year.

So, if you’ve been thinking our Mays are not as nice as they once used to be, it appears the data supports this. Just why this might be happening is anyone’s guess. Will this trend continue? We’ll have to wait and see, but judging by last year and this year, the answer is looking to be “yes.”

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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