Whitefish Range

Despite 3 to 5 inches of welcome new snow, avalanche hazards remain isolated.  Check for exceptions to the generally safe conditions on steep, upper elevation slopes. In this terrain, you may find small pockets of drifted snow at the tops of chutes and on the lee sides of exposed ridges and summits. This terrain also harbors weak layers close enough to the surface to be collapsed by the weight of a person or snowmachine. You can find great riding on wind-sheltered slopes where the pitch stays the same throughout or gets less steep.    

Three to 10 inches of low-density snow over the past two days. It's no snow-pocalypse, but we'll take it. The fresh snow is enough to create new avalanche hazards in some parts of the region, while potentially reactivating older concerns. Wind speeds and accumulations have varied across the region, so the changes are localized. In general, though, slopes where you find 8 inches or more of recent or drifted snow will be the most dangerous.  Shooting cracks and whumpfing collapses are clear signs of this danger. 

Thursday, observers reported triggering small slabs of drifted snow in John F. Stevens Canyon and soft, breakable cornices in the southern Whitefish Range. I expect that triggering similar slabs will be the most widespread hazard today. Look for soft but dense slabs of drifted snow about a foot thick near ridges at mid and upper elevations. They'll be most common and largest on northerly and easterly slopes near the crest of the Swan and Flathead Ranges, and the peaks around Lake McDonald. They'll be most dangerous where they can carry you into or over terrain that increases the chances of deep burials or trauma - gullies, trees, or cliffs. 

Because the fresh snow has fallen on a buffet of weak or slick interfaces, the new snow hazards won't be limited to areas prone to collecting drifted snow. The weak snow surfaces include facets and surface hoar that developed in the recent cold weather, as well as wind-polished crusts. As the fresh snow consolidates above these layers, slabs will likely become reactive to the weight of a person or snowmachine. Most will not produce enough debris to bury or injure a person. The exceptions will be about 8 inches or more thick. These can break wide enough to catch a person, and the debris may run fast and far on underlying crusts. Thursday, the signs of this danger were obvious - audible collapses and cracks shooting up to 25 feet away. On very steep slopes where the snow hasn't yet consolidated into a slab, you may be able to trigger sluffs of loose, cohesionless snow that can pose a danger above terrain traps. 

For two weeks, we've been highlighting slopes above about 7000 feet where the 1/13 storm didn't deposit a hard crust. In this terrain, a person could still trigger slabs that break 1 to 2 feet deep on weak layers of buried surface hoar or facets near crusts. With incremental loading by recent snow over the past few days, those concerns linger on steep slopes with likely trigger points. Those are spots where the weak layers tend to be most developed, or are closer to the surface and more easily collapsed by the weight of a person or snowmachine.  Visualize slopes with convex profiles (steeper further downslope) or that have variable snowdepths due to underlying talus and rock outcrops, or because of erosion by cross-slope or upslope winds. Look for terrain like this and then find alternatives, so you can avoid exposing yourself and your party to the potential of triggering large and dangerous slabs.