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 2013
On May 21, an EF2 tornado touched down near the small community of Glenarm, Ontario about west of Fenelon Falls, and Environment Canada confirmed that the roof of a home was torn off by the tornado and a barn was destroyed. No injuries were reported in this storm. This was Ontario's second tornado of the 2013 season.
A large, slow moving system produced 86 tornadoes across the Great Plains in the last week of May. Many tornadoes, some strong to violent, touched down across Kansas and Nebraska from the 27th through the 29th, with weaker tornadoes recorded in other states. One of the most notable tornadoes of the outbreak was a wide wedge tornado that struck near El Reno, Oklahoma on the evening of May 31. It was the widest tornado ever recorded. The tornado was initially rated an EF5, with estimated winds being measured at > by a mobile Doppler radar; however, the worst damage was rated EF3, thus on August 30, 2013, the tornado's rating was downgraded to EF3. Eight deaths were attributed to this tornado including four storm chasers; TWISTEX project leader Tim Samaras, his son Paul, fellow chaser Carl Young, and amateur storm chaser Richard Charles Henderson. That same evening, a large EF3 tornado moved through several St. Louis suburbs, resulting in major damage and two injuries. In total, the outbreak resulted in 93 tornadoes.