TULSA - Deadly tornadoes that have raked communities in middle America over the past week, including Monday’s twister that carved a path of destruction through the Oklahoma City suburb of Moore, contradict what had been a relatively quiet start of the 2013 tornado season.
This is the furthest into May the U.S. had gone without registering an EF1 or stronger tornado, which are the types that can cause damage. That’s according to Harold Brooks, a research meteorologist at the National Severe Storms Laboratory in Norman, Okla.
An unusually cool spring and unusual upper air patterns kept the funnel clouds at bay until mid-May, or about a month after they typically begin their deadly dance in this part of the country. But that calm melted away with the recent rise in temperatures and humidity in the Plains and Midwest that produced ideal temperatures for deadly tornadoes in Oklahoma and Texas since last Wednesday.
“What had happened over the last week, and for quite a while there, was a ridge in the atmosphere that stayed over the western United States, and that is a pretty unfavorable pattern for tornadoes,” Brooks said. “But, over the last few days, the ridge has moved east and the trough flow came over central United States. On Saturday, we got a lot of moisture that returned from Gulf of Mexico, and when you bring those ingredients together, something’s going to happen.”
Tornado strikes have fallen markedly in the U.S. since the 2011 season, when the country was hit over and over by killer twisters. April 2011 had 497 EF1 or stronger tornadoes. That’s not only a record, but it’s more than the next two highest months combined, Brooks said.
From June 2010 through May 2011, there were 1,050 EF1 or stronger tornadoes, which was a record high for a 12-month period. Just a year later, a record tornado drought began. From May 2011 through April 2013, there were only 217 tornadoes, 30 fewer than the old record.
As Monday’s devastating touchdown in Moore shows, a slow start to the season says nothing about how it how it could eventually shape up.
“It was quiet in February through April; that doesn’t tell us anything that will happen in May,” Brooks said.
As Moore residents frantically searched the wreckage of schools and homes destroyed by Monday’s strike, communities elsewhere in Oklahoma and the region were bracing for the possibility of new funnel clouds or huge hail stones.
Hours before the Moore strike, National Weather Service meteorologist Peter Snyder predicted that twisters could touch down in the region and other areas to the east.
“There’s a good environment for super cell development, and it could develop a squall line that produces 70 mph wind and clusters of thunderstorms,” Snyder said. “It’s a similar situation [as Sunday] but it will affect points east today.”
The deadly tornado strikes began Wednesday, when a twister outbreak in North Texas killed six people and injured dozens of others, many in the community of Granbury.
A huge storm system that moved through the Plains and Midwest on Sunday produced tornadoes in Kansas and Iowa, but it was Oklahoma that bore the brunt of the destruction, with at least 39 injured throughout the state and two deaths from a tornado strike near Shawnee, 30 miles east of Moore.
Information for this article was contributed by Seth Borenstein of The Associated Press.
Front Section, Pages 1 on 05/21/2013