Avalanche Forecast

Issued: Dec 26th, 2020 8:00AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

Kate Ryan,

Although decreasing in likelihood, triggered persistent weak layers could result in avalanches running to valley bottom.

There is a Special Avalanche Warning in effect. Click Here to access.

Summary

Weather Forecast

A pacific frontal system will cross the BC interior today, gradually dissipating Sunday morning

Today: Mainly cloudy with isolated flurries (5cm). Alpine high -7 C. Wind SW 20-30 km/h

Tonight: Mainly cloudy with isolated flurries (5cm). Alpine low -9 C. Wind SW 30 km/h

Tomorrow: Cloudy with sunny periods, no precip. Alpine high -8 C. Wind W 10 km/h

Snowpack Summary

The recent storm dropped 120cm snow and was accompanied by warm temps and strong S-SW winds, followed by strong N winds. Weak layers: Dec 13 surface hoar/facets are down 70-110cm, Dec 7 crust/surface hoar layer is down 110-130cm+. The Nov 5 crust lingers near the base of the snowpack.

Avalanche Summary

Thursday, a skier accidental size 2 slab avalanche occurred in a SE Couloir on Mt Afton.

Wednesday, avalanche control by MOT produced two size 4 avalanches just west of the Glacier Park boundary. Bagheera SE face went size 3.5 overnight Wednesday. The suspected failure plane for these avalanches is the December 7th crust/ facet interface.

Confidence

Due to the number of field observations

Problems

Wind Slabs

An icon showing Wind Slabs

120cm of storm snow in the past week with mild temperatures and strong S/SW winds. Post storm strong N'ly winds reverse loaded S'ly aspects too, expect slab formation on all aspects in the alpine and exposed areas of TL.

  • If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
  • Keep an eye out for reverse loading created by N-NE winds earlier in the week.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

The Dec 7th surface hoar/crust and Dec 13th surface hoar layers have produced very large avalanches this past week, up to size 4! Wind slabs have the potential to step down to this layer.

  • Be aware of the potential for wide propagations.
  • Be wary of large alpine slopes that did not previously avalanche.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 3

Valid until: Dec 27th, 2020 8:00AM