Flathead Range & Glacier NP

Be alert for fresh, reactive slabs of dense, wind-drifted snow at upper elevations. These can be dangerous where they're more than about 8 inches thick or above terrain traps. Minimize your chances of triggering a large avalanche that breaks several feet deep in old weak layers by avoiding likely trigger points, such as steep break-overs or slopes where the snowpack appears thin and rocky. Expect the danger to rise to Moderate at mid-elevations if snowfall exceeds forecasts.

The hunt for snow that's not topped with a breakable crust may take you into the terrain where you're most likely to find small but reactive slabs of wind-blown snow. That's because areas where recently-deposited rime or freezing rain crusts are thinnest  - or topped with 4 to 6 inches of recent powder- are also the areas with the most snow available for transport. And winds have finally increased to speeds where they can blow snow around, with upper-elevation stations reporting hourly averages of 15 to 30 mph overnight and gusts of 20 to 60 mph. These winds are blowing loose snow around and creating isolated slabs of drifted snow. Sticking to sheltered, mid-elevation slopes will offer the most pleasant, lowest-risk riding today. 

We continue to see evidence that deeply buried weak layers are strengthening and becoming unreactive to the weight of a rider or machine. No propagation in snowpack tests, few reported signs of instability since New Year's Eve, and no reported triggered avalanches on these layers since Dec. 29th, even with people riding steeper terrain. 

 I'm still leery of some slopes, however. Tuesday, my partner and I looked down the steep, southerly chutes dropping down from the Tunnel Ridge weather station. The chutes were a series of short snowfields above rollovers where the slopes disappeared from view, many with rock outcrops dotting the sides. Windward, sunny terrain with variable snow depths and lots of trigger points. Just the kind of terrain where one is likely to get surprised. No thanks. 

Tuesday's snow surfaces are getting buried today in many locations. Many of these -surface hoar, near-surface facets, facets under thin rain or rime crusts - could form future weak layers, particularly if they are buried initially with thin, soft slabs. Pay attention if you're out the next few days to how these layers are behaving. They won't pose a hazard now unless they're buried by drifted snow. But they may be a future problem where they're breaking or collapsing easily in snowpack tests or on test slopes. If today's storm overproduces, the future could be now; expect a widespread Storm Slab problem to develop at mid-elevations.