Today, March 11, the Western Montana Avalanche Center released its preliminary study of the Mt. Jumbo avalanche that plowed into Van Buren Street, killing one woman and trapping three others almost two weeks ago.

Avalanche Specialist Steve Karkanen says that heavy snowfall, cold weather, and strong winds helped to create an event that he described as "historic."

"It was such an unusual avalanche," Karkanen said. "The last part of February and the first part of March in most years, that mountain is bare and has no snow on it. The other thing that's unusual is that it was loaded on the west slope from winds that came out of the east. Typically Mt. Jumbo, on that particular slope, is wind scoured it gets prevailing winds from the west so we typically don't see much snow that gets loaded on those upper reaches.

Strong winds had been shooting through Hellgate canyon during Friday morning, pushing more snow on top of what was already an extremely abnormal amount of snow for that section of Mt. Jumbo

The strange weather conditions helped make an avalanche that was almost as powerful as it could have possibly been.

It's never been documented that an avalanche that size has hit the valley floor," Karkanen. "In the scale of 1 to 5, we are calling that a size 4, which means that it could go bigger at some point, based at the measurements that we have."

The study showed an average snow depth of about three feet and a total plummet of 2,200 feet from crown to terminus.

Steve Karkanen: