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March 18, 2010 / Dave Gorham

Coming Soon: El Niño and the Tornado

At the risk of making YourWeatherBlog begin to sound like YourElNiñoBlog, I wanted to tie the two main weather features of the coming couple of months into one sentence: El Niño will likely enhance the spring severe weather season with more frequent storms, stronger storms and more tornadoes.



Tornadoes can generate wind speeds of 250mph or more near the center of the tornado. Photo: NOAA and U.S. Department of Commerce.

So far 2010 has gotten off to a slow start as far as tornadoes are concerned: 162 is average by this time of year, yet there have been only about a third or less of that as we move into the last week or so of March. In fact, the month of February had only one tornado reported across the United States. But Saturday is the first day of spring and spring is the true beginning of tornado season.

What does El Niño bring to the severe season? Nothing we haven’t seen already. Namely, wetter and cooler weather for the southern States. Now, the cooler weather may act to stabilize the lower atmosphere, but the increased frequency of El Niño-driven Pacific storms should overpower the somewhat cooler atmosphere and allow the opportunity for more frequent thunderstorms.

Thanks to El Niño and more frequent Pacific storms, the southern States are expected to remain cooler than normal for April. Image: ImpactWeather StormWatch.

In addition, the steering current of these storms, the southern jet stream known as the subtropical jet stream, will add an additional level of severe storm potential. Consider the open sunroof in your car. As you speed down the highway, have you noticed how there is an updraft in the cabin? Things like papers or the smoke of a cigarette are lifted upward and then out of the car? The same phenomena occurs with a jet stream over a thunderstorm: the rapidly rushing air of the jet stream over a thunderstorm tends to help lift air currents within the thunderstorm higher and faster. This allows a moderate thunderstorm to grow into a strong thunderstorm and a strong thunderstorm to grow into a severe thunderstorm.

An open sunroof and a speeding car creates an updraft or an exhaust mechanism inside your car. Photo: Flickr

It would be nice if the lower-than-normal number of tornadoes continued through the months of spring. It doesn’t look like that will happen. Once again we can thank El Niño for a sour turn to the usual weather conditions across the southern United States (perhaps southern Europe, as well).

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