"The EF Scale, which became operational on February 1, 2007, is used to assign a tornado a 'rating' based on estimated wind speeds and related damage," explains the NWS website.
While Arizona sees up to 10 tornadoes per year, almost all of them are in the northeastern part of the state.
The last twister to hit the Valley was four years ago according to NWS experts. On average, the NWS told 3TV the Valley only sees one tornado every five to 10 years – the strongest on record being an EF1 which carries winds up to 110 mph.
The experts said straight-line winds from microburst activity during the monsoon season can produce damage just as severe as, or even more so than weak tornadoes.
The strongest tornado in Arizona history, according to the NWS, was an EF3 (winds of 136-165 mph) twister in the Prescott area.