Avalanche Forecast
Issued: Mar 27th, 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.
cgarritty,
Avalanche Canada
Snowfall and high winds should continue overnight and Sunday, making Sunday a dangerous day for travel in avalanche terrain. Stick to simple terrain free of overhead hazard to manage the risk. Danger may be one step lower in areas where 30 cm or less accumulates during the storm.
Summary
Confidence
Weather Forecast
Saturday night: Cloudy with continuing snowfall bringing another 10-20 cm of new snow. Extreme southwest winds.
Sunday: Cloudy with continuing snowfall bringing another 5-15 cm and two day snow totals to 30-70 cm. Moderate to strong west winds easing and shifting north over the day. Alpine temperatures cooling to around -11 over the day as freezing levels return to valley bottom.
Monday: A mix of sun and cloud. Light to moderate west winds. Alpine high temperatures around -13.
Tuesday: Cloudy with scattered flurries and less than 5 cm of new snow. Moderate west winds. Alpine high temperatures around -7.
Avalanche Summary
We don't yet have observations from Saturday's storm in the region, but light initial accumulations at weather stations suggest its impacts may be delayed to Saturday night and Sunday. Continuing snowfall and high winds over this period should make for active avalanche conditions on Sunday. The west slope of the region is still where the greatest accumulations are expected.
Explosives control in the wake of the last storm yielded many storm and wind slabs in the size 2-2.5 range in the Table River Valley on Thursday, with one size 3 (very large) release. Evidence of Wednesday's widespread natural cycle was observed during the same mission, with many more size 3 avalanches noted on a greater range of terrain.
Snowpack Summary
New snow totals from the weekend storm are expected to reach 30-70 cm by end of day on Sunday. Amounts may be lighter in typically lower snowfall areas on the east slope. Much of this snowfall is forecast to be accompanied by extreme south and southwest winds. Rain is expected below about 1200 metres.
The new snow has buried melt freeze crusts at lower elevations and on solar aspects and otherwise added to 30 to 50+ cm of settling dry snow from this week's storm. The new snow may be particularly reactive to triggers where it buries crust.
Cornices have also become very large along ridgelines and always have the possibility of failing naturally or from the weight of a human.
A weak layer of facets buried mid-February may now be found around 120 to 150 cm deep, or shallower in the east of the region and in thin snowpack areas. The most likely place to trigger this layer is where the snowpack is shallow in alpine terrain. Large loads, such a cornice falls or multiple sleds on the same slope often trigger slopes that a single rider couldn't trigger on their own.
Terrain and Travel
- Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
- Storm slab size and sensitivity to triggering will likely increase through the day.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Problems
Storm Slabs
A widespread new storm slab problem is expected to form in the region as 2-day storm totals of up to 70 cm materialize by the end of the day Sunday. Manage the rising danger by sticking to simple, low angle, low consequence slopes and avoiding overhead hazard.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
The persistent slab problem is most likely on the eastern slopes of the region (e.g., Kakwa, Tumbler Ridge) and in areas where the snowpack is thin. Steep, rocky slopes with a shallow or thin to thick snowpack in the alpine are the most likely places to trigger buried weak layers. This problem likely won't go away until substantial melt-freeze cycling occurs.
Aspects: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Mar 29th, 2021 4:00PM
