Avalanche Forecast
Issued: Dec 11th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Deep Persistent Slabs.
rbuhler,
Avalanche Canada
Recently formed storm slabs are expected to remain reactive to human triggers on Sunday and conservative terrain selection remains essential. Use extra caution around steep south-facing slopes if the sun is shining bright in the afternoon.
Summary
Confidence
Weather Forecast
A ridge of high pressure is expected to build on Sunday bringing cold and dry conditions to the region for the next few days.
Saturday Overnight: Partly cloudy, patchy snow flurries 1-5 cm, moderate SW winds, treeline temperature around -12 °C.
Sunday: A mix of sun and cloud, light to moderate SW winds, treeline high around -8 °C.
Monday: A mix of sun and cloud, light E winds, treeline high around -12 °C.
Tuesday: Mostly sunny, light to moderate SE winds, treeline high around -15 °C.
Avalanche Summary
On Friday, the North Rockies field team reported shooting cracks and were triggering small slabs with ski cuts near treeline in the Pine Pass area. Explosive control on Wednesday and Thursday produced wind slabs in exposed high elevation terrain up to size 2.5.
On Sunday, the recent storm snow is expected to remain reactive to human triggering, especially in wind affected areas. If the sun is shining on Sunday afternoon, the reactivity of the slab may increase on south facing slopes. While the basal weakness appears to be gaining strength in the region, it still may be reactive to heavy triggers and a smaller storm slab avalanche still has the potential to step down to a deeper layer resulting in a much larger avalanche.
Snowpack Summary
On Friday and Saturday, up to 20 cm of new snow was reported bringing the weekly storm snow accumulation to 50-70 cm. This new snow came in with strong winds from the southwest which formed highly reactive slabs in wind exposed terrain. Below the past week's storm snow, some surface hoar had been observed in sheltered areas at and below treeline but this appears to be isolated and has not been reactive in recent days. The November 27th rain crust is now buried 40-100cm and extends as high as 1500m elevation.
The lower snowpack consists of a series of early season crusts. Cold temperatures will have promoted faceting around these crusts. Shallow alpine slopes along the eastern side of the Rockies towards Jasper may have weaker, faceted snow near the ground.
Snowpack depths at treeline range from 60cm-200cm, with the shallower value mainly on the eastern side of the range. The alpine snowpack ranges from 150cm-200cm.
Terrain and Travel
- Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
- Minimize exposure to sun-exposed slopes when the solar radiation is strong.
Problems
Storm Slabs
Recent storm snow along with strong winds have formed a widespread storm slab at higher elevations. While the thickness and reactivity of this slab likely varies throughout the region, it is expected to be most reactive in wind exposed terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
An early season crust at the base of the snowpack has shown reactivity in the southeast corner of the forecast region. While this layer likely needs a heavy trigger like a cornice collapse or smaller avalanche stepping down, human triggering may still be possible on thin rocky slopes in this part of the region.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 12th, 2021 4:00PM
