Avalanche Forecast
Issued: Mar 26th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Loose Wet and Persistent Slabs.
cgarritty,
Avalanche Canada
Another storm is barreling toward the region Friday night. Heavy snowfall and strong to extreme winds mean a natural avalanche cycle is likely to begin by the end of the day. Danger may be a step lower in lower snowfall areas where 20 cm or less accumulates.
Summary
Confidence
Moderate - Forecast snowfall amounts are uncertain.
Weather Forecast
Friday night: Cloudy with flurries bringing 5-15 cm of new snow. Winds becoming strong to extreme west.
Saturday: Cloudy with continuing snowfall bringing 10-20 cm of new snow, continuing overnight. Extreme southwest winds. Alpine high temperatures around -2 with freezing levels to 1700 metres.
Sunday: Cloudy with 10-20 cm from overnight and another 5-15 cm during the day bringing 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 -10 over the day as freezing levels return to valley bottom.
Monday: A mix of sun and cloud. Light to moderate north winds shifting west. Alpine high temperatures around -13.
Avalanche Summary
Explosives control in the Table River Valley on Thursday yielded many storm and wind slabs in the size 2-2.5 range, 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.
Looking forward, we have another storm of similar strength taking aim at the region Friday night through Saturday. Natural avalanche activity will likely follow a similar pattern, especially in the west of the region where the greatest accumulations are expected.
Snowpack Summary
Up to 35 cm of new snow is expected to accumulate along the west slope of the region over Friday night and Saturday, closer to 15 cm in typically lower snowfall areas on the east slope. Weather models call for this snowfall to be accompanied by extreme south and southwest winds. Rain is expected below about 1200 metres.
The new snow will bury melt freeze crusts at lower elevations and on solar aspects and otherwise add to 30 to 50+ cm of settling dry snow from this week's storm. Our 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 100 to 120 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.
- Be alert to conditions that change with elevation and wind exposure.
Problems
Storm Slabs
Up to 35 cm of new snow and strong to extreme winds will quickly form a widespread new storm slab problem for Saturday. Manage the rising danger by sticking to simple, low angle, low consequence slopes and avoiding overhead hazard. A natural avalanche cycle is expected by the end of the day.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Loose Wet
Rain soaked storm snow and moist new snow accumulations will be likely to shed from steep slopes naturally and with human triggers at lower elevations on Saturday.
Aspects: All aspects.
Elevations: Below Treeline.
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 27th, 2021 4:00PM
