Idaho’s location, nestled between the Rocky Mountains and high desert plateaus, typically shields it from the meteorological conditions that fuel the most violent tornadoes common in the Great Plains. The state sees a relatively low frequency of these rotating columns of air compared to states further east. While Idaho is not considered a part of “Tornado Alley,” it is still susceptible to these events, most of which are weaker and short-lived. Understanding the risk and history of these storms requires looking at the most recent confirmed event within the context of the state’s historical averages and extremes.
The Details of the Last Confirmed Tornado
The last confirmed tornado in Idaho touched down on July 25, 2024, near Glenns Ferry in Elmore County. This event was classified as a landspout tornado, a type of weak rotation that forms from the ground up under a rapidly growing cumulus cloud, rather than descending from a supercell thunderstorm. The National Weather Service (NWS) office in Boise confirmed the event and assigned it an Enhanced Fujita Scale Zero (EF-0) rating based on the observed damage.
The EF-0 rating is the lowest on the scale and corresponds to estimated wind speeds between 65 and 85 miles per hour. The short-lived vortex had a path length of only about 0.3 miles and an approximate width of 100 feet. Damage reports indicated a damaged roof, several downed trees, and power lines that sustained damage, even producing power flashes as debris struck them.
The landspout gained strength by tapping into a nearby thunderstorm’s updraft, which helped organize the rotating air already present near the surface. Although the damage was limited to property and resulted in no injuries or fatalities, the confirmation highlights that tornadoes can occur in the high desert region of southern Idaho. The official determination relied heavily on public video submissions, as radar data alone did not clearly indicate a tornado.
Historical Averages and Tornado Frequency in Idaho
Tornado activity in Idaho is significantly lower than in other parts of the country, averaging about 2.5 tornadoes annually. These events are strongly seasonal, with the peak time for activity occurring in the late spring and early summer months, particularly June. Historically, June has accounted for the highest number of recorded events in the state.
The majority of these storms are weak, falling into the EF-0 or EF-1 categories, which is typical for states west of the Great Plains. Geographically, the highest concentration of activity tends to be in the southeastern and southern portions of the state, particularly across the Snake River Plain. Counties like Bingham, Jefferson, and Power have historically recorded the most tornadoes.
This pattern of low frequency and low intensity places Idaho among the states with the least tornado activity per square mile. The infrequency of the storms means there is a relatively low risk of experiencing a high-magnitude event. The low annual average reflects the mountain ranges and arid climate that often suppress the atmospheric ingredients necessary for significant tornado development.
Idaho’s Most Powerful Recorded Tornadoes
The severity of tornadoes is measured using the Enhanced Fujita (EF) Scale, which assigns a rating from EF-0 (weakest) to EF-5 (strongest) based on wind speed estimates and observed damage. While most Idaho tornadoes are confined to the lower end of this scale, the state has recorded a few historically significant, higher-magnitude storms. These stronger events demonstrate the potential for localized severe weather, even given the state’s low tornado frequency.
One notable historical event was the F3 tornado that struck Nez Perce County on June 7, 1936, recorded as the deadliest in the state’s history with two fatalities. Another significant event was the 1973 Roert tornado, also cited as one of Idaho’s deadliest. A more recent example was the F2 tornado that tore through Blackfoot in 2006, leaving behind a path of destruction. The 1978 Idaho Falls tornado also caused extensive damage, impacting nine homes and twenty-three businesses with roof damage.