Tornado
The United States has the most tornadoes of any country, nearly four times more than estimated in all of Europe, excluding waterspouts. This is mostly due to the unique geography of the continent. North America is a large continent that extends from the tropics north into arctic areas, and has no major east-west mountain range to block air flow between these two areas. In the middle latitudes, where most tornadoes of the world occur, the Rocky Mountains block moisture and buckle the atmospheric flow, forcing drier air at mid-levels of the troposphere due to downsloped winds, and causing the formation of a low pressure area downwind to the east of the mountains. Increased westerly flow off the Rockies force the formation of a dry line when the flow aloft is strong, while the Gulf of Mexico fuels abundant low-level moisture in the southerly flow to its east. This unique topography allows for frequent collisions of warm and cold air, the conditions that breed strong, long-lived storms throughout the year. A large portion of these tornadoes form in an area of the central United States known as Tornado Alley. This area extends into Canada, particularly Ontario and the Prairie Provinces, although southeast Quebec, the interior of British Columbia, and western New Brunswick are also tornado-prone. Tornadoes also occur across northeastern Mexico.
Tornadoes of 2008
The largest severe weather outbreak in Europe in 2008 took place. At least 20 tornadoes were reported across a large section of the continent. At least one person was killed and one other was injured in northwestern Russia, with the fatality taking place in Udmurtiya where a house was destroyed. The strongest tornado was at least an F2. Other tornadoes were reported in Germany, Italy, Poland, Croatia, Latvia, the Netherlands and Denmark.
After a lull in activity, several small tornado events took place in the second week of July, mostly in the northern Plains region. On July 7, several tornadoes were reported near the Manitoba/North Dakota border causing damage to trees, roofs, and boats. Among the areas hit were Bottineau, Rolette and Towner Counties in North Dakota as well as Lake Metigoshe and Turtle Mountain Provincial Park in Manitoba. An EF3 tornado destroyed 12 homes and damaged 18 homes in Rolla and destroyed eight homes and damaged 47 homes in Belcourt. An EF1 tornado also touched down in Green Lake County, Wisconsin. On July 8, a barn roof was removed by an EF0 tornado that hit Whitley County, Indiana. An EF1 tornado ripped off part of a warehouse roof in Petersburg, Virginia on July 9.