Arizona is not typically associated with the destructive power of tornadoes, unlike the Great Plains region often called Tornado Alley. The desert and mountainous geography present atmospheric challenges that make the conditions necessary for tornadic activity difficult to sustain. While the state experiences severe weather, the frequency of confirmed tornado touchdowns remains very low.
The Most Recent Confirmed Tornado
The last fully documented tornado to strike a metropolitan area in Arizona occurred on the night of July 2, 2024, in Tucson, located in Pima County. The National Weather Service (NWS) confirmed that the storm was an EF-1 on the Enhanced Fujita (EF) scale, which rates tornadoes based on the damage they cause. An EF-1 is classified as a weak tornado, with wind speeds ranging from 86 to 110 miles per hour.
The twister touched down around 10:45 PM near the city’s south side, specifically impacting the Rita Ranch area. It tracked approximately 3.25 miles before lifting back into the atmosphere. Damage reports indicated that the tornado was responsible for uprooting numerous large trees and causing damage to roofs, including the removal of tiles. A metal shipping container was also tossed by the powerful winds during the brief, ten-minute event.
The path of the tornado primarily followed a line along Valencia Road near Old Vail Road. Fortunately, no injuries or fatalities were reported as a result of the event, which is consistent with the generally weaker nature of tornadoes recorded in the state. The quick formation and short duration of the storm meant that it appeared and dissipated between radar scans, making it difficult for forecasters to issue a timely warning.
Historical Context and Frequency
Arizona’s average annual tornado count is significantly lower than that of states in the central United States. On average, the state records between two and five confirmed tornadoes per year. This low frequency emphasizes the atypical nature of tornadic activity in the region.
The majority of tornadoes in Arizona occur during the late summer months, primarily from July through September. This period coincides with the North American Monsoon, which brings a surge of moisture into the desert Southwest. August historically stands out as the peak month for tornado occurrence, accounting for the highest percentage of recorded events.
While summer monsoonal storms are the most common source, a secondary season for tornadoes can occur during the late fall and winter. These cooler-season events are typically associated with strong cold fronts moving across the state. The vast majority of Arizona’s tornadoes are classified as weak, falling into the EF0 or EF1 categories.
Meteorological Factors Governing Arizona Tornadoes
The formation of tornadoes in Arizona is limited by unique atmospheric and geographical constraints, which explains their relative infrequency. A primary missing ingredient for the powerful, long-track supercell tornadoes common in the Plains is sufficient wind shear. Wind shear refers to the change in wind speed or direction with height, which is necessary to create the horizontal rotation that can be tilted vertically into a tornado.
During the summer monsoon season, a high-pressure ridge often sits over the Southwest, which tends to suppress the strong upper-level winds required to produce significant vertical wind shear. The storms that do form are often convective, powered by intense surface heating and moisture brought in by the monsoon. The resulting storms frequently feature high cloud bases, meaning the rotating column of air has a longer distance to descend to the ground.
The tornadoes that do form, particularly in the summer, are often landspouts, which are non-supercell tornadoes. Landspouts develop from the ground up when surface winds converge along boundaries like outflow from a thunderstorm. An updraft from a storm overhead can then pull this low-level rotation upward, forming a tornado without the deep, persistent rotation characteristic of a supercell.
Geographically, the most tornado-prone areas tend to be the central and southern counties, including Maricopa, Coconino, and Pima. The mountainous regions and high plateaus further complicate the development of organized, long-lived storm systems. Consequently, Arizona’s tornadoes are typically short-lived and weak, reflecting the state’s challenging environment for severe weather.