The Washington Post

2012 vs . 2011 tornadoes: A study in contrasts

Tornadoes in 2012 (turquoise line) and 2011 (green line) compared to average (black line) (NOAA)

NOAA’s Storm Prediction Center provides the following summary of this year’s numbers:

After a busy start, tornado events in the U.S. in 2012 have dropped well below the expected normal. The preliminary total of 757 tornadoes is about 400 tornadoes below what might be expected in a typical year. This chart shows that in late 2011, the annual running total was over 400 tornadoes above normal. This depicts the dramatic variability that can occur in tornado numbers from one year to the next.

Even if tornado activity is quite a bit above average the rest of the year, 2012 will be hard-pressed to reach the average annual total of 1,300.

The 2012 tornado season got off to a superfast start, with above normal activity into April. But then, as the storm track (and jet stream) took a huge jog north, tornado frequency (relative to average) tailed off. This was especially true over the summer as a huge ridge of high pressure (or heat dome) became established over the middle part of the country. Extraordinarily dry conditions and drought affected a sprawling region from the Rocky mountains to parts of the East Coast. This cut way down on tornado numbers.

But as the storm track shifted into Canada, our northern neighbor experienced a very active tornado season. The Weather Network reported Canada experienced more tornadoes in July than the entire U.S., with Saskatchewan the new tornado alley:

Saskatchewan has had upwards of thirty tornadoes this summer, with most happening in July. In a typical year, there’s an average of ten to twelve tornadoes in the province. What’s more, Saskatchewan alone had the same amount of tornadoes in July as the entire United States.

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.


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