Tornadoes and storms hit parts of the United States

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  • A tornado photographed at Tipton, Oklahoma on the 7th November 2011. Source: Steve Grabman/NOAA

    Storm reports across the USA on the 7th November 2011. Source NOAA

    Storm reports across the USA on the 8th November 2011. Source NOAA

    Satellite image of the Bering Sea storm on the 8th November 2011. Source: NASA

  • Tornadoes and storms hit parts of the United States
    12.11.2011 14:54

     

    Damaging thunderstorms spread east across the southern Great Plains of the United States during Monday 7th and Tuesday 8th of November, producing strong winds, flash flooding, large hail, and several tornadoes. Western Alaska was also battered by an exceptionally strong storm this week, which produced damaging hurricane force winds, and produced a storm surge which flooded many low-lying coastal communities.

    Intense thunderstorms began to break out across Oklahoma and northern Texas on Sunday 6th November, ahead of an eastward moving cold front in association with a low pressure system situated across western Oklahoma. Heavy rainfall and flash flooding affected parts of central Oklahoma last Sunday night with as much as 9 inches (228mm) recorded during the event. The storm system then gradually moved east into Monday with supercell thunderstorm generation occurring, which spawned several tornadoes. The strongest tornado recorded was just to the east of Tipton, Tillman County, in the south of Oklahoma. This tornado was graded an EF4 on the Enhanced Fujita Scale used to measure the strength and severity of tornadoes. This was the first EF4 tornado to hit Oklahoma in November since records began in 1950, with estimated maximum wind speeds of between 166-200mph. The rating was based primarily on the damage it caused to a research station; as due to the fact that the strongest winds within a tornado are highly localised, it is often impossible to determine the strongest winds within these systems. However, unlike most events the Tillman tornado came very close to the Fort Cobb weather station, allowing a detailed analysis of the storm before it was destroyed by flying debris. A pressure drop of 10mb was recorded in just 3 minutes as the tornado approached, with a maximum wind gust of 90mph just before the station was destroyed.

    A total of 21 tornadoes were sighted during the event of the 8/9 November, located across southern Oklahoma, eastern Texas and north-east Louisiana, but the rest were nowhere near as intense as the Tillman Tornado.

    The southern Great Plains wasn’t the only region of the US to experience strong winds and flooding, with the western coast of Alaska experiencing a powerful extra-tropical storm which moved north through the Bering Sea. Hurricane force winds disrupted power supplies, and a storm surge as high as 10ft (3m) above normal high tide flooded many coastal communities. Winds gusted above 85mph at some locations, with the system being the most powerful storm to hit the region since November 1974. The storm also produced significant snowfalls and blizzards further inland where the temperatures were near or below freezing, with between 3 to 8 inches (7-20cm) of snow recorded in the state’s largest city, Anchorage, by the end of Thursday.

    By: Chris Burton