Tornado Widths– NOAA Makes Changes In Procedure

By Paul Homewood

NOAA have claimed that the El Reno tornado, in Oklahoma in May, was the widest tornado on record. As I pointed out at the time, there was evidence to suggest that the width of earlier tornadoes had been underestimated. One tornado, in particular, Hale County, Texas, in May 1968, was officially categorised as 3000 yards wide, but the original Storm Data Publication described the width as “between two to three miles wide”. Vague at best, but also indicative that the width varied between two to three miles.

Thanks to a reader, I have discovered that there was a policy change at NWS in 1994, to report “maximum width” instead of “mean path width”.

The reference to this was contained in a paper by Harold Brooks, “On the Relationship of Tornado Path Length and Width to Intensity”, published in 2003. (Page 318)

http://www.nssl.noaa.gov/users/brooks/public_html/papers/lengthwidth.pdf

Although, according to Brooks, the policy change occurred in 1994, this does not explain why a tornado in 1997 was similarly underestimated – see here.

Either way, it is clear that claims of “widest ever” for the El Reno tornado need to be taken with a pinch of salt.

Here is what NOAA says:

On May 31st, a cold front moving through the Central and Southern Plains spawned severe weather from Oklahoma to Indiana. There were 30 preliminary reports of tornadoes in eight states. The hardest hit areas included the Oklahoma City Metro area, the St. Louis metro area, and locations north of Tulsa, Oklahoma. In the Oklahoma City area, three tornadoes were confirmed, including an EF-0 and EF-1 which hit part of Moore, Oklahoma. The deadliest tornado of the outbreak hit just west of Oklahoma City, in the town of El Reno.

The EF-5 tornado had estimated winds well over 200 miles per hour (estimated from Doppler radar), was on the ground for 16.2 miles and had an estimated path width of 2.6 miles. The 2.6 miles width surpasses the Hallam, Nebraska tornado of May 2004 as the widest tornado on record for the United States and subsequently the world. The Hallam EF-4 tornado was 2.5 miles wide. It was also the 60th confirmed EF-5 (or F-5 prior to 2007) tornado in the U.S. in the 1950-present record. Parts of El Reno were also hit by an EF-5 tornado in May 2011, and prior to the Moore EF-5 was the last EF-5 confirmed in the nation.

Highways in the area had severe traffic congestion due to the rush hour commute, creating a very dangerous scenario. The tornado resulted in at least nine fatalities, seven of which were in automobiles. The fatality count might have been higher, but the tornado hit a relatively sparsely populated area on the south side of El Reno. The storms in Oklahoma were also accompanied by heavy rainfall that led to flash flooding. Numerous people had to be rescued from the flood waters, and an estimated 100,000 homes and businesses lost power during the event. An additional nine people were killed due to severe winds and the flash flooding. More information on this tornado is available from the National Weather Service.

Source: http://www.ncdc.noaa.gov/sotc/tornadoes/2013/5

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