According to catastrophe modeling firm AIR Worldwide, a severe thunderstorm outbreak producing damaging wind, up to baseball-sized hail, heavy rainfall and more than a dozen tornadoes across five states—from Texas to Illinois—left a path of destruction over the weekend of April 23, and April 24, 2011. The storms damaged thousands of residential and commercial buildings, downed trees, and knocked out power to as many as 54,000 customers.
The storm also caused major travel delays in St. Louis, Missouri when a tornado struck a large section of the the main terminal of the Lambert-St. Louis International Airport, ripping off a portion of the roof and the airport’s C concourse. The storm prompted the governor of Missouri to declare a state of emergency in areas affected by the tornadoes. While power has been restored to thousands of residents, some 26,000 customers in Missouri and Illinois are still without power.
“The storms formed when a strong area of low pressure moved out of the Rocky Mountains and into the Central Plains earlier in the week, pulling in colder air,” explained Dr. Tim Doggett, principal scientist at AIR Worldwide. “The cold front interacted with a warm humid air mass that had moved in from the Gulf of Mexico. A strong jet stream led to increased wind shear and a change in wind direction, facilitating the formation of severe rotating thunderstorms, hail, and high winds.”
The largest tornadic storm originated in the east central region of Missouri. While several tornados touched down, the most devastating one touched down in St. Louis on Friday evening at 8 p.m. Dubbed the “Good Friday Tornado”, it left a track 22 miles long and almost a half mile wide, causing EF-4 level damage and producing wind gusts of 166 to 200 mph. It was the strongest tornado to hit St. Louis in 44 years.
Along the tornado’s path, heavy damage was reported to single and multi-family wood frame and unreinforced masonry homes. “At the level of winds produced by an EF-3 or EF-4 tornado even well-engineered buildings that are designed to survive very intense winds may sustain some damage to non-structural components such as wall cladding, windows and roofs,” said Dr. Doggett. “Tornadic winds passing over the roof act like air moving over an airplane wing: uplift is created, which tends to raise the roof vertically.” As real-time footage from the airport in St. Louis vividly illustrates, winds are then able to enter, pressurizing the building and blowing out windows—and with them, contents. Debris generated from the damaged structures (e.g., roof panels, shingles, glasses) becomes a source for damage to other properties.
According to the National Weather Services, the greatest damage occurred in the communities of Maryland Heights, Bridgeton, St. Ann, Edmundson, Lambert-St. Louis International Airport, Berkeley, and Ferguson in St. Louis County, Missouri, and in Madison County near Granite City, Illinois.
AIR continues to monitor the onset of the 2011 severe thunderstorm season and will provide updates as warranted.
Source : AIR Worldwide Press Release
