Many of you have already seen this footage below, but I thought it would be interesting for WUWT readers to get a look at the cause behind it. Meteorologist Mike Smith, from WeatherData, sent an interesting picture and description of the incident vua email that I wanted to share. I’ve added some links and visuals also. – Anthony
Mike Smith writes: A “downburst” is a unique form of extreme winds unknown to meteorologists prior to 1977 when it was discovered by Drs. Ted Fujita and Horace Byers. While they can occur anywhere, the Dallas area has bitter experience with downbursts.
Delta Airlines’ flight 191 crashed in a downburst at DFW International Airport August 2, 1985, killing 135. In the quarter century since that horrible August day, meteorologists have made tremendous strides forecasting and warning of these small, but deadly, storms.
WeatherData Services, Inc., (an AccuWeather Company), applied that knowledge at 2:50pm May 2, 2009 when we issued a SkyGuard® warning of 65 mph winds for a client located in the Dallas suburb of Irving, TX. Based on radar, the winds struck between 3:10 and 3:15pm.
A post-storm survey by the National Weather Service determined winds were “nearly 70 mph.”
These winds collapsed the Dallas Cowboys’ practice facility where a “mini-camp” was in progress. According to NBC Sports, Cowboys’ owner Jerry Jones stated, “We did not get [a] good warning.” This may be because governmental sources did not issue a warning until 3:06pm, 16 minutes after WeatherData’s and just moments before the winds occurred.
Here is some background info on downbursts:
A downburst is created by an area of significantly rain-cooled air that, after hitting ground level, spreads out in all directions producing strong winds. Unlike winds in a tornado, winds in a downburst are directed outwards from the point where it hits land or water. Dry downbursts are associated with thunderstorms with very little rain, while wet downbursts are created by thunderstorms with high amounts of rainfall. Microbursts and macrobursts are downbursts at very small and larger scales respectively. Another variety, the heat burst, is created by vertical currents on the backside of old outflow boundaries and squall lines where rainfall is lacking. Heat bursts generate significantly higher temperatures due to the lack of rain-cooled air in their formation. Downbursts create vertical wind shear or microburst which is dangerous to aviation.
A downburst is created by a column of sinking air that, after hitting ground level, spreads out in all directions and is capable of producing damaging straight-line winds of over 150 mph (240 km/h), often producing damage similar to, but distinguishable from, that caused by tornadoes. This is because the physical properties of a downburst are completely different from those of a tornado. Downburst damage will radiate from a central point as the descending column spreads out when impacting the surface, whereas tornado damage tends towards convergent damage consistent with rotating winds. To differentiate between tornado damage and damage from a downburst, the term straight-line winds is applied to damage from microbursts.
Downbursts are particularly strong downdrafts from thunderstorms. Downbursts in air that is precipitation free or contains virga are known as dry downbursts; those accompanied with precipitation are known as wet downbursts. Most downbursts are less than 2.5 miles (4 km) in extent: these are called microbursts. Downbursts larger than 2.5 miles (4 km) in extent are sometimes called macrobursts. Downbursts can occur over large areas. In the extreme case, a derecho can cover a huge area more than 200 miles (320 km) wide and over 1000 miles (1600 km) long, lasting up to 12 hours or more, and is associated with some of the most intense straight-line winds, but the generative process is somewhat different from that of most downbursts.
Here is why a downburst is so dangerous to aviation.