Flathead Range & Glacier NP

Keep an eye on the clock, and an eye on slopes above you. Dangerous wet snow avalanches will become likely on or below steep slopes receiving sustained sun, or where the surface snow is wetting for the first time. Collapsing cornices can drag a rider off a ridge, or drop dense debris onto slopes below. In the highest, coldest terrain, a lingering concern is a hard slab breaking on deeply-buried weak layers. In this terrain, avoid steep, unsupported slopes with variable snow depths. 

Weather summary and outlook*: Mostly cloudy skies kept temperatures above freezing overnight at most stations below 7000 feet. The exceptions were in the Whitefish Range. Skies cleared early this morning, and will remain mostly sunny until mid-afternoon. At and near ridgelines, expect gusty west-southwest winds and air temperatures again near 40 degrees. Overnight, skies look to be overcast, with a few hours of freezing temperatures above about 6000 feet. Saturday, expect shallow morning inversions, mostly cloudy skies, highs again near 40 degrees at 6000 feet, and diminished winds. 

Snowpack and Avalanche Discussion: Several weather factors are conspiring to increase the wet snow avalanche danger today: a warming trend over the past two days, a snow surface that's a few days old, no overnight refreeze of the snow surface, and mostly sunny skies. So the snowpack this morning is already warm, and with more direct radiation input, will heat quickly on all but the most shaded terrain at upper elevations. Triggered and natural sluffs of wet snow are likely on steep slopes where the snow surface is wetting for the first time, and on steep slopes where there's a foot or more of wet, cohesionless older snow. These conditions are more widespread in the Flathead Range, where it's been 48 hours or more since the snow surface refroze. The Flathead Range also has continuous snow above about 3800 feet, with long, steep avalanche paths. Natural wet snow avalanches may run full track in some of these paths today. I expect nearly all wet snow avalanches today to involve loose snow, because a snow structure that favors wet slab avalanches exists only on isolated slopes. Wet snow avalanche hazards may be a wee bit slower to develop in the Whitefish Range, thanks to a brief period of freezing temperatures early this morning.

Today's warm, sunny weather also increases the threat posed by Cornices and Glide avalanches. The first seems to pose more hazard today, with cornices sagging and tugging at their roots in the warm temperatures and sun. Looking up, they're an obvious threat. On ridges, the danger may be less obvious. Numerous accidents have occurred when cornices collapse under human-powered and motorized riders, including one two weeks ago in California. Stay well back from the edges of cornices, ideally downslope of the crests on the windward sides of ridges. Stay out from under open glide cracks and slopes with a rumpled, moguled look that shows the snowpack has been sliding downslope.

And then there's the lingering hazard of large hard slabs failing on mid-winter persistent weak layers. The current warming is a test of whether they remain unstable. Given that the test is ongoing, I'd avoid upper elevation shady terrain that's convex in shape, looks to have variable snow depths, and is steeper than about 35 degrees. 

*The National Weather Service has stopped producing their Snow and Avalanche Guidance product, which provides us with forecasted sky, temperature, wind, and precipitation values for 12-hour periods. For the rest of the season, we'll include a weather summary and outlook in the discussion.