Catastrophe modeling firm AIR Worldwide reported that the huge storm system that impacted the United States from New Mexico to Michigan and Georgia over the Christmas holiday weekend delivered at least nine tornadoes in North Texas. In addition to tornadoes, the storm hit a large swath of the country with flash floods, blizzards, hail and freezing rain.
It is too early to tell the extent of damage caused by the Texas tornadoes, which were mostly concentrated in the vicinity of Dallas, the fourth most populous metropolitan area in the country. According to local officials, as many as 1,450 homes may have been damaged or destroyed.
The most serious damage was caused by a tornado that hit Rowlett in Dallas and Rockwall counties with EF-3 winds gusting between 136 and 165 mph. It then struck nearby Garland, a northeastern suburb of Dallas, as an EF-4 tornado, which typically has wind gusts between 166 and 200 mph. The line of damage caused by this tornado — the deadliest to hit the Dallas area since an EF-4 tornado hit Garland on May 9, 1927 — is about 13 miles long.
An additional EF-2 tornado struck near Copeville in Collin County and Blue Ridge, Ovilla/Glenn Heights, Hubbard, Ennis, Eustace, Sulphur Springs, Emory, and Sunnyvale were also hit by tornadoes. The Texas Gov. Greg Abbott has declared Collin, Dallas, Ellis, and Rockwall counties disaster areas.
Damage surveys are still ongoing, and it is too soon to have a complete account of the damage caused, according to AIR Worldwide.
Initial reports indicate that 600 structures were damaged in Garland, most of them single-family homes, and that a similar number may have been damaged in Rowlett. An RV park near Sunnyvale in Dallas County is reported to have sustained damage to 63 structures, and 116 structures are known to have been damaged in Glenn Heights in Dallas and Ellis counties, 29 of them seriously.
In addition to damaged structures, there was extensive damage to vehicles, power lines, and trees.
According to AIR, commercial buildings are, on average, less vulnerable than residential structures or automobiles. Older commercial buildings with reinforced concrete or brick exteriors can behave better than modern commercial structures, particularly those with a great deal of glass. Light-metal structures, which are the most vulnerable to high winds, may suffer severe to complete damage from tornadoes.
The tornado activity on December 26 was accurately forecast by the Storm Prediction Center and appropriate warnings were issued. All but one of the reported tornadoes occurred in the enhanced risk area indicated. Tornadoes can appear at any time of the year, but they occur less frequently in winter.
On the Gulf Coast, peak “tornado season” is during the spring. From 1950–2012, only 12 December days have seen EF-4 or EF-5 tornadoes. Tornadoes can also happen at any time of the day or night, but most occur between 4 p.m. and 9 p.m. The Garland Tornado struck just prior to 7 p.m.
AIR said the U.S. tornado count for 2015 is well below average. While an average of 1,200 to 1,300 tornadoes occur annually in the United States, the Storm Prediction Center at the National Weather Service reports that only 1,056 tornadoes had been recorded as of Dec. 27.
Source: AIR Worldwide
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