After the devastation we’ve already seen, the worst of tornado season could be yet to come

Despite the deadly and destructive tornado outbreaks we've seen over the past three weeks, May 2013 is actually tallying up to be a fairly quiet month for tornadoes compared to previous years. With May usually the most active month for tornadoes, hopefully that will mean a quiet June as well, but can we really count on that?

Historically, although tornadoes are seen in every month of the year, the trends usually show lower numbers in the fall, winter and early spring, then increasing into April, peaking in May and then tapering off through June, July and August. May and June see the most, overall, with April and July coming in at a distant 3rd and 4th place.

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That trend was skewed in the past two years, though. For both 2011 and 2012, the peak of the tornado season actually happened in April. This was especially true for 2011, when April saw an astounding 758 tornadoes, ranking it as the most active month for tornadoes on record. Both years had strong La Niña weather patterns in the Pacific Ocean, bringing unusually warm spring weather for the southern United States, which may have helped to kick off the tornado season early. For 2011, that was also combined with unusually cold weather in the northern and western United States, which probably made that particular season so bad.

Other than 2011's sudden jump from 78 tornadoes in March to 758 in April, there has still been the same trend in the numbers of gradually increasing to the peak for 2010 and 2012, and all three years saw the gradually decrease afterward.

So, what, if anything, does that say about what we're seeing so far this year, and what we may see to come?

For this year, forecasts were already calling for an active severe storm season, with 'tornado alley' shifted more to the east. This is remarkably similar to what was seen in 2010. That year, the season got off to a late start, just as we're seeing now, and tornado alley was similarly shifted further to the east. The peak of that season straddled May and June, with roughly similar numbers both months.

With the persistent cold weather into the early part of the season, it's possible that we may simply see fewer tornadoes this year, overall. Given the incredible devastation and tragic deaths we've already seen over the last three weeks, we can only hope that's the case.

At the same time though, we can't ignore the possibility that the weather so far this year may have delayed the peak of the tornado season, pushing it back so that we will actually see much more activity in the months to come.

Of course, yesterday, June 1st, was the start of the 2013 Atlantic Hurricane Season, which is already forecast by the National Hurricane Center to be 'active or extremely active'. Nothing is currently brewing in the Atlantic that's of any significant concern, but dealing with a potentially active hurricane season at the same time as the possibility of a late peak to the tornado season is a dire situation, to be sure.

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Here in Canada, where the tornado season usually peaks in June and July, there have already been five tornadoes in Ontario so far — an EF1 near Shelburne on April 18th, three EF0 tornadoes on May 21st (one east of Lake Simcoe and two between the lake and Georgian Bay), and one witnessed by storm chaser Dave Patrick near Arthur and Mount Forest on Saturday, June 1st. These all happened as part of the same weather systems that spawned all the tornadoes in the United States, so an increase in tornadoes for the US in June (if that happens) could mean more for southern Ontario as well.

In addition, we've seen several storms that have produced 'downbursts' and 'microbursts', such as the thunderstorm that passed through Brampton on Wednesday morning, and the storm that hit Shawville, QC on Friday afternoon.

Out west, where the strongest tornadoes tend to happen in Canada (including two if the deadliest, in Edmonton in 1987 and Pine Lake in 2000), there hasn't been much activity yet. However, the forecast for this month is talking about potential tornado activity in Alberta and Saskatchewan starting next week and continuing until the end of the month. With a slow start to the season in the U.S., and the shift of tornado alley to the east, there may be a similar delay and shift in the Prairies this year, but experts are still advising Canadians to prepare, just in case.

The Government of Canada lists tornado facts and warning signs, as well as what do to if you are in a tornado, on their website.

(Images courtesy: Reuters, NOAA)

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