Avalanche Forecast

Issued: Nov 27th, 2017 5:12PM

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

mgrist, Avalanche Canada

North Columbia.

New snow and southerly winds will be driving avalanche danger on Tuesday. Avoid exposure to avalanche terrain during periods of rapid loading by rain, snow, or wind.

Summary

Confidence

Low - Intensity of incoming weather systems is uncertain

Weather Forecast

The next system arrives on Tuesday with modest accumulations of snow and more seasonal temperatures. TUESDAY: Snow (5-15cm) during the day with another 5-10cm possible overnight. Moderate southerly ridgetop winds. Freezing level around 1000 m.WEDNESDAY: Clearing throughout the day. Moderate westerly ridgetop winds. Freezing level around 1200 m. THURSDAY: Cloudy with isolated flurries. Light to moderate southwesterly ridgetop winds. Freezing level around 1100 m.

Avalanche Summary

On Monday, several storm slabs to Size 2.5 were reported near Rogers Pass, on northerly aspects between 2000 - 2700m. On Saturday we received reports of a skier-triggered Size 1 storm slab on a NW aspect at 2150m elevation in Rogers Pass. See here for the MIN report. A natural avalanche cycle is expected on Sunday into early Monday in areas where rain falls on dry snow. We currently have very limited observations in this region. Please submit your observations to the Mountain Information Network (MIN).

Snowpack Summary

The warm temperatures and rain on Sunday resulted in a crust (November 27th crust) up to approximately 1900m, which was covered by up to 10cm of snow at higher elevations as temperatures cooled significantly. This November 27th crust could prove to be an excellent sliding layer when additional snow falls on Tuesday. Previously, 15 to 30 cm of snow over the past few days sits on a 2cm thick crust formed on November 23rd. The heavy rain last week rapidly shrunk the snowpack and transitioned much of the snowpack from dry to moist snow. The depth of the snowpack varies greatly with elevation. Recent reports suggest the average depth is 200+cm in the alpine, 100-150cm at treeline, and decreasing rapidly below treeline where the primary hazards are rocks, stumps, and open creeks. A major feature in the snowpack is a 2-5 cm thick crust which was formed around Halloween and can be found approximately 70-100cm down at treeline elevations. We currently have very limited snowpack observations within this region and it is critical to supplement this information with your own observations.

Problems

Storm Slabs

A natural avalanche cycle is expected on Tuesday with the incoming snow. Be particularly cautious where the November 27th crust is prominent.

Avoid exposure to avalanche terrain during periods of rapid loading by rain, snow, or wind.Watch for signs of instability such as whumpfing, cracking, or recent natural avalanches.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

Rapid loading by rain or snow will increase the likelihood of avalanches occurring on this layer.

Avoid exposure to avalanche terrain during periods of rapid loading by rain, snow, or wind.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Nov 28th, 2017 2:00PM