Weather Wise: A rare storm for Montana

HELENA — What a wet, weekend storm. Several towns in Montana, including Helena, Great Falls and Bozeman, had a record amount of precipitation. Most of Montana saw between 1 and 2 and a half inches of rain, with some spots getting more than 3 inches of rain, and the storm is not quite over with yet, so precipitation totals could still increase.

Steady to heavy rain fell across the state seemingly all weekend long, creating areas of minor flooding, making for tough travel conditions on the roads, and really limiting outdoor activities. If you, your kids, and or your pets went a little stir crazy, it might be nice to know that a storm like that does not come around too often.

In fact, with storm totals of 1-3″ of rain over the course of 2-3 days, the frequency of a storm like that is between about 2 to every 5 years. storms are described by their recurrence interval or return period, which is the average time between events of that size. For those who make wagers out there, a storm like this has about a 20% chance of happening any given year. This does not mean a storm like this will happen every 5 years. It’s possible it could happen every 2 years, or 10 years apart, or twice in a row, even.

Over 20 years, you could expect a storm like that about 4 times, but the actual number could vary. A one-in-5-year storm is relatively common but still a significant weather event that probably won’t happen again for a little while.