Bitterroot

Large human-triggered persistent slab avalanches are possible at middle and upper elevations. Wet loose avalanches will become likely at all aspects and elevations by the afternoon. If you see signs of wet snow today, such as roller balls, pinwheels, recent wet loose avalanches, and snow that is soft and unsupportable underneath your skis or sled, stick to slopes less than 30 degrees.

February is here, and with it comes another day of spring-like weather before winter expectantly returns!

This week has been dominated by unseasonably warm, clear, and dry weather. Mountain temperatures reached the 50’s (F) on multiple days. The snowpack got wet and warm on all aspects and elevations. We saw an impressive natural avalanche cycle; forecasters observed over 50 avalanches between the three zones. Most of these ran as small point release avalanches, entraining snow to the ground. Some triggered larger persistent slab avalanches. While we may be past the point of peak avalanche activity now that most avalanche paths have run, plenty of remaining hazard exists. Some avalanche paths still have not yet run, and overhanging snow still clings to upper elevation slopes.

There is some uncertainty as to how well the snow refroze overnight and how deep the meltwater penetrated into the snowpack in some areas. In places with a more shallow snowpack, such as the Rattlesnake, meltwater reached the ground. But in some areas, such as the Central Bitterroot, which has the deepest snowpack within our forecast region, the snow is still dry near the ground.

If meltwater reaches buried persistent weak layers today in an area that has not yet slid, an avalanche could release with characteristics reminiscent of a wet slab avalanche. Dig down into the snow and look for poor snowpack structure and wet snow. Moist and wet snow have a distinct tendency to stick together and form a snowball when you squeeze it with your hand. In very wet snow, water can be pressed out by moderately squeezing the snow. It is still possible to find some combination of buried crusts, surface hoar, facets, and depth hoar. Any of these layers will be more unstable if wet. The persistent slab problem is touchiest in the Southern Bitterroot, where a layer of buried surface hoar is well preserved and has produced several skier triggered avalanches and close calls.

It will be imperative that you watch for wet snow as you travel through backcountry terrain today. While uncertainty is high, recognizing signs of an impending wet snow avalanche is easy. Look for roller balls, pinwheels, and recent wet loose avalanches. Notice wet snow underneath you that feels soft and unsupportable. You may even punch through to the ground. Typical persistent slab red flags such as cracking and collapsing may not be obvious. So if you see signs of wet snow today, stick to low angle slopes.

With this warm weather, the snow settled significantly, and the depth of the snow dropped. Lower elevation slopes lost much of the meager snowpack that had built up through January. One observer noted that on Lolo Pass, southwest aspects are completely melted out below 6000 ft. Watch out for ground hazards such as downed logs, rocks, and stumps, as well as dry ground and less snow coverage in previously well-covered areas.

Now, onto the much anticipated return of winter! A weather system is entering our region and will begin to impact the mountains tonight. Temperatures will drop, and light precipitation is expected. Snow levels will stay elevated and likely not accumulate until Friday. The Central and Southern Bitterroot are favored to receive a few inches of snow. The weather is forecasted to remain stormy through the weekend.

Ski and sled safe!