Avalanche Forecast
Issued: Feb 5th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
swerner,
Avalanche Canada
Storm slabs are likely reactive to skier and rider triggering on Saturday, especially where they sit above a weak layer down 30-70 cm. Obvious clues of instability like natural avalanche activity may not exist, so conservative terrain choices are best.
Summary
Confidence
Weather Forecast
An arctic front gradually pushes its way South bringing cold air and some light embedded flurries. A cold northwest wind will persist through the forecast period.
Saturday: Cloudy with flurries 5-10 cm. Alpine temperatures near -5 and light wind from the West.
Sunday: Mix of sun and cloud. Alpine temperatures near -15 with moderate ridgetop wind from the northwest.
Monday: A mix of sun and cloud. Alpine temperatures near -25 and mostly light wind from the northeast.
Avalanche Summary
On Friday, numerous loose-dry avalanches were reported up to size 2 during the storm in steep terrain.
On Thursday, reports indicated several small features were reactive up to size 1 on the late-January buried surface hoar interface. I suspect that once the persistent slab gains more cohesion and stiffens, this problem may be more widespread. Even a small avalanche can catch you by surprise and have enough mass to push you into a terrain trap below.
Fresh storm slabs may be touchy on Saturday, especially where they sit above surface hoar, crust, or old surface facets.
Snowpack Summary
Up to 30 cm of recent low-density snow fell by Friday bringing 40-80 cm of accumulative storm snow from the past week over a variety of older snow surfaces. These old surfaces, at upper elevations (upper treeline and the alpine), include surface hoar in locations sheltered from the wind, surface facets, and stiff wind affected snow. At lower elevations (lower treeline and below treeline) 10-30 cm of snow sits above isolated pockets of surface hoar and a crust that is more predominant on solar aspects.
Additional snow and changing wind combined with cohesion may stress these potentially weak interfaces, creating the persistent slab problem. This MIN from last weekend is a good example: MIN Report.
The mid-pack seems to be well settled. Deep persistent layers appear to have mostly gone inactive with the exception of the Bear Pass area and the far reaches south of Kitimat.
Terrain and Travel
- 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.
- Watch your sluff: it may run faster and further than you expect.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Problems
Storm Slabs
20-40 cm of new storm snow has slowly accumulated over the past two days. Changing wind directions may deposit deeper and stiffer slabs on multiple aspects. I suspect that anywhere the new snow feels stiff and more cohesive the slab may be more reactive, especially where it sits above a buried weak layer.
Loose-dry avalanches are likely from steeper slopes where there is little cohesion in the recent storm snow.
Large, looming cornices exist along ridgelines.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
30-70 cm sits above a buried weak interface that consists of surface hoar, facets, and/ or a crust. Forecast snow and wind will likely add cohesion and load to these weak layers resulting in a reactive persistent slab problem.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 6th, 2021 4:00PM
