Timing is everything. Conditions will be generally stable, and avalanches are unlikely while surfaces are frozen. As temperatures rise under mostly sunny skies, avalanches will become possible as surface crusts break down and more than the upper few inches of the snowpack become wet. Get good corn snow conditions while surfaces are soft, but before they become unsupportable. Cooling temperatures and clouds will reduce the wet snow hazard later in the day.
If this afternoon’s snow adds up to more than a few inches, fresh drifts will become unstable.
I am uncertain about the extent to which this hazard will develop today based on the shifting weather pattern, but I will certainly be looking for indicators of decreasing stability.
While snow will begin falling this afternoon in the mountains around Cooke City, Bozeman, and Big Sky, it won’t arrive early enough to affect avalanche conditions much today. Until snow accumulates to more than a few inches, wet snow instability remains the primary avalanche concern. I hope that everyone gets a window of pleasant corn skiing and riding, but refrozen surfaces may be the conditions today.
So, avalanches…
Pluses for stability: Clear skies overnight allowed snow surfaces to radiate heat and form thin refrozen crusts. Moderate winds are cooling surfaces. Temperatures will drop this afternoon. And increasing cloud cover will shade snow surfaces. Conditions may change quickly, but these changes are relatively easy to recognize.
Negatives for stability: Overnight temperatures were a few degrees warmer than last night and remained above freezing, except at high elevations around Big Sky and Cooke City. This morning will be mostly sunny and warm.
Conditions will be generally stable, and avalanches are unlikely while surfaces are frozen. As temperatures rise under mostly sunny skies, avalanches become possible as surface crusts break down and more than the upper few inches of the snowpack become wet. Wet loose avalanches will generally be small, but near cliffs and rocks, additional warming can result in an unsupportable snowpack, and slides can gouge deeper. On Friday, Mark noted a natural wet loose avalanche in Cooke City (observation), and on Thursday, Ian and Andrea observed cornice-triggered wet snow avalanches on Lionhead Ridge that were large enough to bury or injure a backcountry traveler (video). Rollerballs and small wet loose avalanches can serve as additional warning signs of decreasing stability, and you can avoid wet snow instability in upper elevations and shadier, north-facing terrain.
Cornice fall is an additional hazard, as large cracks are opening on ridges (observation). Limit time below these large overhanging drifts on warm spring days. Ensure you are on solid ground well back from the edge when traveling along corniced ridgelines.
The danger is MODERATE throughout the forecast area due to my uncertainty about the timing of increasing cloud cover and cooling temperatures relative to the increase of wet snow hazard. If surfaces remain frozen and supportable, avalanches are unlikely until snow begins to fall and drift later this afternoon. The danger is LOW in the upper elevations of the Gallatin and Madison Ranges, and near Cooke City, where temperatures are cooler.
