Tornado Alley Shifts East as Delayed Tornado Season Begins




April 2
, 2010
Jon Auciello and Senior Meteorologist Henry Margusity
AccuWeather


This year's tornado season is expected to shift farther eastward into the Midwest and become more active in late April through June.

The greatest concentration of tornadoes is reported between March and August each year in "Tornado Alley," which includes portions of Texas, Oklahoma, Kansas, Nebraska and South Dakota.

This spring, AccuWeather.com meteorologists expect tornado activity will increase farther east into the Midwest instead of the traditional Tornado Alley.

Tornado season usually begins in March, but this year, there has been a lack of tornadoes. A total of 64 tornadoes have occurred as of March 29. On average, 225 tornadoes occur by this date.

Several reasons account for the lack for tornadoes in 2010, an El Niño year.

1. A cooler-than-normal Gulf of Mexico.

2. Jet stream displaced farther south than normal due to the El Niño.

3. Persistent cool weather in the Plains and South.

The frequency of tornadoes will increase as the El Niño begins to weaken and the Gulf of Mexico sea surface temperatures warm.

The Midwest appears particularly primed for additional tornado outbreaks this year rather than the typical Tornado Alley states because of the predicted storm track and the proximity of Gulf moisture should be present by late April.

AccuWeather.com analyzed tornado reports dating back to 1950 from the Storm Prediction Center during April, May and June of 1958, 1966, 1978, 1988, 1993, 1995 and 2003, the most recent years categorized as El Niño events.

Two patterns emerged from this information: many states had fewer tornadoes reported early in severe weather season than normal, and then higher totals emerged in the following months for some states.

In April, the southern tier of states, including Oklahoma, Texas, Louisiana, Mississippi, Alabama and Florida, reported an increased number of tornadoes than they typically see. Meanwhile, nearly all states to the north of that line saw fewer twisters in El Niño years.

However, the severe weather often returned with a vengeance in the states lining the Mississippi River and many Southern states in May, as a much higher-than-normal amount of tornado reports occurred in those years.

Once June arrives, tornado activity begins to normalize overall across the country. The one exception is South Dakota, which has seen nearly double the amount of twisters in June El Niño years than others.

http://www.latimes.com/news/nationworld/nation/wire/ktla-earthquake,0,6948498.story