North Rockies

A cold weekend will reduce the potential for avalanches in the short term. If the weather forecast is right, warming coupled with reduced winds and clear, sunny conditions will begin to increase danger later in the forecast period. 

A natural cycle of avalanches occurred early in the week. This cycle was related to the new snow and winds that came through the region Monday night and through Tuesday. These avalanches were storm slabs, often failing on surface hoar in wind sheltered locations. At upper elevations windslabs were the problem and it's not certain whether there was surface hoar in play or not. 

In the last couple of days, natural activity seems to have largely died out. Windslabs and cornices were being triggered by explosives, these were up to size three where cornices were involved and smaller where only windslabs. These windslabs and cornices will likely become more difficult (but not impossible) to trigger Saturday in the cold temperatures then could become more reactive again later in the weekend and almost certainly on Monday if temperatures rise as predicted.

In areas sheltered from wind, it's going to be all about slab development. If the snow remains cold, dry, and unconsolidated it's unlikely there will be any significant avalanche activity through Sunday morning. But as temperatures rise late Sunday or early Monday, the snow will likely become more cohesive. This could be quite subtle so it'll be important to watch carefully as even seemingly minor changes in cohesion could result in soft slab avalanches being triggered on the surface hoar layers or the suncrust that are discussed in the snowpack summary.

Friday Night: No significant precipitation. Moderate to locally strong winds from the north, northeast, and east at ridgetop. Light and variable winds below treeline. Temperatures -25 to -30. 

Saturday: No significant precipitation. Moderate to locally strong winds from the north, northeast, and east at ridgetop, easing overnight. Light and variable winds below treeline.Temperatures -15 to -20. 

Sunday: No significant precipitation. Light to moderate winds from the north, northeast, and east at ridgetop. Light and variable winds below treeline.Temperatures -10 to -15. 

Monday: No significant precipitation. Light to moderate winds from the north, northwest, and west at ridgetop. Light and variable winds below treeline. Temperatures -5 to -10 in the alpine, near zero below treeline.

Early in the week, a suncrust formed on sun-exposed slopes, and in the southern part of the region, a second surface hoar layer was reported on shaded slopes. Where they exist, these layers could become increasingly sensitive and unstable if warming occurs late in the period as forecast.   

Up to 60cm of storm snow fell early in the week. In wind sheltered locations the storm snow remains cold, dry, and generally unconsolidated. At treeline and in the alpine the storm snow has been blown around by moderate to strong alpine and treeline winds in the last few days. Winds have shifted direction from south and southwest to north and northeast so wind slabs have formed on most aspects at upper elevations. Cornices are also growing on many aspects. Warming and solar radiation could increase the sensitivity to triggering for these layers late in the period. 

If temperatures warm up as forecast we will likely see increasing cohesion in places where surface snow is currently unconsolidated. This would form soft slabs on the suncrust and surface hoar layers. Warming will also increase the sensitivity of wind slabs and cornices that are currently somewhat unreactive.

• Recent wind has varied in direction so watch for wind slabs on all aspects.
• Approach lee and cross-loaded slopes with caution.
• Avoid steep slopes when air temperatures are warm, or solar radiation is strong.