Posted: May 22, 2013 10:11 PM by Russ Thomas - StormTracker Weather Center
MISSOULA - Devastating tornadoes, like the ones seen in parts of Oklahoma and Kansas this weekend are an all too familiar scene in the Southern Plains. While Montana does not see volatile weather nearly as often, this is the time of year we should pay attention to the skies.
Tornados in Western Montana are a rare occurrence, but they do happen. In all, fourteen reported tornadoes have touched down over the last 62 years, including three in Flathead, Lake, and Ravalli Counties, and two in Missoula. The number of average yearly tornadoes across Montana during that span is six, but Western Montana averages one tornado every four and a half years. So, why does the Eastern half of the state see more severe storms and tornadoes?
The availability of low level moisture is the main factor. By and large, Montana is a very dry state however, Central and Eastern Montana is more susceptible to receiving monsoonal moisture from the Gulf of Mexico. When this moisture interacts with a cold front moving over the Rockies, the warm moist air rises creating strong storms. Windshear within these storms helps to generate these tornadoes. The most recent example of a powerful tornado came in June of 2010 in Billings, where an EF2 tornado tore through the town with a reported wind speed of 130mph.
Occasionally, Western Montana does receive enough moisture to create the potential for tornadoes. In fact, the most likely time for severe weather and tornado development begins in late May. Between late May and mid-July, that combination of available moisture and an active jet stream can create a focal point for tornadoes to develop.
The bottom line is that, while tornado development is rare, it can occur, and now is the time to pay close attention to the skies, as we transition from late spring to early summer.
Data from the past 62 years shows most of Montana's tornadoes occur in the eastern part of the state, specifically Valley County.