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 2018
There were 1,169 preliminary reports of tornadoes in the United States in 2018, of which at least 987 have been confirmed. Fifteen tornado-related deaths were confirmed worldwide; ten in the United States, four in Brazil, and one in Canada. The United States saw below-average numbers of tornadoes in 2018, with near record low tornado amounts in the typical peak month of May. Elsewhere in North America, the only officially-rated violent (EF4-EF5) tornado of the year occurred near the town of Alonsa, Manitoba on August 3; therefore, making 2018 the first year that the United States has not had a violent tornado touchdown through the entire year. With only 10 fatalities in the United States, 2018 also had the lowest number of tornado-related fatalities on record in the United States.16 tornadoes were reported in the United States in January, of which 15 were confirmed.