February 7, 2008
Meteorologists Study Deadly Tornado Outbreak
Warm moist air and a shifting weather pattern courtesy of the La Nina phenomenon aided in the development of the Feb. 5 tornadoes, which killed at least 50 people and were among the 15th deadliest in U.S. recorded history. But meteorologists are now trying to explain why the tornadoes occurred so early in the year.
It was farther north than most February tornadoes and stronger, Joseph Schaefer, director of the Storm Prediction Center in Norman, Okla., told Associated Press.
Tornadoes do occur in February. In 1971, a deadlier February outbreak in the Mississippi Delta killed 121 people. A study conducted by Schaefer two years ago, found that winter tornadoes in parts of the South occur more frequently and are stronger when there is a La Nina, a cooling of Pacific waters that is the flip side of the better known El Nino.
February tornadoes usually pop up near the Gulf Coast, not in Kentucky or Tennessee, said University of Oklahoma meteorology professor Howard Bluestein.
A heavy contributing factor was the warm weather. It was 84 degrees in Oklahoma before the storm front moved through on its path of destruction. On Tuesday, 97 weather stations broke or tied records in Arkansas, Alabama, Tennessee and Kentucky - the hardest-hit states, according to Associated Press.
Still, meteorologists said there is not enough recorded historical evidence of such storms to blame global warming at this point, but Tuesday's tornadoes had all of the key deadly elements: warm air near the ground; high winds; and warm moist air coming north from the Gulf of Mexico.
Schaefer told Associated Press, La Nina doesn't specifically cause tornadoes, it helps shift the jet stream, pushing storms from the West and moisture from the Gulf into the necessary collision course over the South.
El Nino, La Nina occurs every few years, and has been changing global weather patterns for a few months now, Mike Halpert, deputy director of the Climate Prediction Center, which monitors La Nina, told Associated Press.
Preliminary figures for January show 136 tornadoes, five tornado deaths and three killer tornadoes, although these figures tend to drop after closer analysis.
Between 1997 and 2007, the average February has 30 tornadoes, killing 9 people. Early reports tallied 68 tornadoes so far this month.
"We're off to a big start for the year," said Greg Carbin, a meteorologist at the storm center.
Meteorologists said that the patterns point to the likelihood of more tornado outbreaks this season.
"As long as the pattern remains the same it can be very active," Schaefer said. "It's not a time to let down your guard."
On the Net:
Storm Prediction Center
University of Oklahoma
Climate Prediction Center