Avalanche Forecast
Issued: Dec 19th, 2020 8:08AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs, Storm Slabs and Persistent Slabs.
jonas hoke,
Natural triggering has slowed, but with strong winds forecast for this afternoon (and heavy snowfall tonight) another natural cycle will begin later today. Avalanche terrain that has not had recent activity should be avoided.
Summary
Weather Forecast
A brief respite from a weak ridge today, then a couple more frontal systems give moderate-heavy snowfall tonight and early next week.
Today: Sunny periods. Alpine High -7 °C. Ridge wind moderate (gusting strong) SW.
Tonight: Snow (20 cm). Low -8 °C. Strong (gusting Extreme) SW wind.
Sunday: Flurries (9 cm). High -6 °C. Mod-Extreme SW wind.
Snowpack Summary
20+ cm of new snow, strong SW winds and warm temps continue to build a sensitive slab at all elevations. Weak layers of concern are Dec 13 surface hoar/facets down 60cm+ and Dec 7 crust/surface hoar layer down 75cm+. The Nov 5 crust lingers near the base of the snowpack but has been unreactive recently.
Avalanche Summary
A widespread cycle of natural and artillery controlled avalanches up to size 3.5 occurred in the highway corridor (and likely in the backcountry) overnight.
There have been several reports of near misses from both skier triggered and natural avalanches in the park over the past few days (see MIN).
Confidence
Problems
Persistent Slabs
The slab continues to build over the Dec 13 surface hoar/facet layer, now down 60+ cm. This layer has been sensitive to human and natural triggering and is reactive at all three elevation bands.
- Use conservative route selection, choose moderate angled and supported terrain with low consequence.
- Avoid overhead exposure during periods of heavy loading from new snow and/or wind.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Storm Slabs
Last nights heavy snowfall, strong SW winds and warm temps were the perfect recipe for building fresh reactive storm slabs.
- If triggered the storm slabs may step down to deeper layers resulting in large avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
70cm+ sits on the Dec 7th weak interface of rain crust/ surface hoar. If triggered the storm slab has potential to step down to this interface triggering large avalanches.
- Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 20th, 2020 8:00AM
