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MONTHLY OUTLOOK | May

Unofficial start to summer: May brings drastic changes


Dr. Doug Gillham
Meteorologist, PhD

Thursday, May 3, 2018, 12:47 PM - It seems like an understatement to say that spring got off to a very slow start across most of Canada. April in particular was unusually cold with many places recording their coldest or one of the coldest Aprils on record, despite some warm weather at the end of the month.

The map below shows the temperatures during April 2018 compared to normal. The various shades of blue and green highlight how widespread the colder-than-normal temperatures were across Canada. Parts of Newfoundland including St. John’s were a notable exception to this pattern as April temperatures were actually warmer than normal.

(COTTAGE REPORT: UNOFFICIAL START TO SUMMER IS AROUND THE CORNER. CHECK OUT OUR COTTAGE REPORT & START PLANNING!)

With the sudden arrival of early summer-like weather during the final week of April and the first week of May, you may be wondering if we are skipping spring and heading straight into summer.  

We are not completely skipping over spring, but we are seeing an accelerated transition from winter to summer across most of Canada. The dominant pattern for May is a striking contrast to what we saw during April as we expect that near seasonal and above seasonal temperatures will dominate the temperature pattern across southern Canada.

Since “normal” during May is 5 to 10 degrees C warmer than it is during April, a transition from a cold April to a normal or warmer-than-normal May is a rather dramatic swing in temperatures.

However, it is still much too early to put away your spring jacket or start planting your garden. Back and forth swings in temperature are normal during May and this year will be no exception.  All of Canada, will see periods of cooler weather during May, including areas where warmer than normal temperatures dominate the month. 

Of concern is that parts of northern Canada will be colder than normal during May and at times that cold air will dive south and interrupt the mild pattern.  However, the periods of cooler weather will not be as persistent or widespread as what we saw during April.

So, while the May will feature a very different weather pattern from April, it is unlikely that May will be the opposite of April. We do not expect that May will be as memorable for warmth as April was memorable for cold. But, we are seeing a quicker than typical transition from late winter-like weather to weather more typical of late spring (and at times early summer) across most Canada.

Watch below: The return of the ridiculously resilient ridge




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