Avalanche Forecast
Regions: North Rockies.
Avalanche danger will increase as new snow and wind form fresh and reactive slabs in leeward terrain features at upper elevations. Wind slabs will be especially touchy where they sit over a crust or surface hoar.
Confidence
Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.
Weather Forecast
Saturday night: Snowfall up to 5 cm. Strong SW wind. Treeline temperature around -5 °C. Freezing level 1000 m.
Sunday: Snowfall 5-10 cm. Strong SW wind. Treeline high around -5 °C. Freezing level 1000 m.
Monday: Snowfall 5-10 cm. Moderate NW wind. Treeline high around -10 °C. Freezing level valley bottom.
Tuesday: Sunny. Light NW wind. Treeline high around -18 °C. Freezing level valley bottom.
Avalanche Summary
The theme over the past week has been wind slab avalanches size 2-3. On Friday, a natural size 2 wind slab was reported on a northeast aspect at 1900 m. Some of the avalanches earlier in the week were failing down to the bedrock in extreme terrain features.
On Friday our field team observed evidence of previous wind slab avalanches having stepped down to deeply buried layers, resulting in large avalanches in Kakwa. This observation has us scratching our heads about the potential for deep avalanches going forward.
Snowpack Summary
New snow and strong wind are forming wind slabs at upper elevations. The new snow falls on highly wind affected surfaces in the alpine, a melt-freeze crust on steep solar aspects and low elevations and a layer of surface hoar in sheltered areas at treeline and below in some areas in the south of the region.
A thin crust may be found 20-30 cm deep, which was the main sliding surface for the wind slab avalanche cycle last weekend. Another crust is found around 70 cm deep but has not shown recent reactivity. The lower snowpack is generally strong and bonded, with one or multiple crusts near the ground. We suspect the lower snowpack could be weak in shallow, rocky, wind-affected slopes east of the divide.
Terrain and Travel
- Watch for avalanche hazard to increase throughout the day.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
Avalanche Problems
Wind Slabs
Watch for fresh wind slabs forming in lee terrain features. Wind slabs will be most reactive and propagate most widely where they sit over a crust (steep solar aspects and low elevations) or a layer of surface hoar (areas in the south of the region).
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 1 - 2