Avalanche Forecast

Issued: Jan 15th, 2021 1:00AM

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

Ryan Shelly, VIAC

Vancouver Island.

Several reports from the mountain snowmobile and backcountry ski community have reported human triggered avalanches size 1-2 on leeward/downwind terrain. The layer responsible for the triggering is a wind slab occurring primarily on convex rolls.

Summary

Past Weather

Past precipitation amounts topped out at 90 mm on the west side of the island with snowfall amounts nearing 45cm on the eastern side. The winds and air temps increased and have factored into a combination of wind slab and developing melt freeze snow surface at the Treeline and Below Treeline elevation bands.

Weather Forecast

Friday: 1-2mm Rain, Winds Moderate from the South increasing to Strong South mountain top winds in the afternoon, Freezing level will reach a high of 1200 meters.Saturday: 5mm Rain and up to 10cm Snow North Island (with majority of precipitation arriving before dawn, Winds Moderate from the NW shifting to Strong NW mountain top winds in afternoon, Freezing level will reach a high of 1150 meters.Sunday: No precipitation expected, Winds Light from the NW, Freezing level will reach a high of 1700 meters.

Terrain Advice

Be cognizant of snow conditions and utilize small slopes to test and investigate the recent storm /wind slab snow and its reactionary properties.Careful and cautious route finding when transitioning from scoured areas into areas of wind loaded snow.Avoid traveling below and above cornice features as they are large and touchy.Avoid open and steep slopes during periods of warming and rain; even small loose wet avalanches will have enough mass to push a mountain traveler into gullies and over cliffs.

Snowpack Summary

Over the past forecast period intermittent moderate to heavy snowfall and intense wind transport was observed. A storm system delivered significant quantities of snow up to 90mm of precipitation on the west side of the island with moderate to strong winds from the South West. Evidence of intense wind transport of snow to North aspects was observed in both the Alpine and Treeline.Overall snowpack depths have been measured from 200cm to 400cm.A variety of crusts exist in the upper snowpack. Numerous snowpack tests indicate that these crusts are now beginning to bond to the storm snow.The mid snowpack has an unreactive 20cm layer of facets that can be found down 120cm and deeper. This layer may be isolated to areas that are sheltered and at higher elevations above 1400 meters presents as a melt freeze crust/ poly grain layer.The lower snowpack is dense and very well settled as many reports from island backcountry users and numerous snow profiles have indicated.

Snowpack Details

Surface: Wind affected snow scoured on exposed South aspects with deep loading on North aspects. Solar aspects becoming moist 1400 meters and below.
Upper: Storm snow and wind slabs from past storms can be found over a crust below 1500 m and over old storm snow above 1500 m.
Mid: A 20cm layer of facets can be found down 100cm plus.
Lower: Well settled and dense.

Confidence

High - Weather models in agreement, sufficient field weather and snowpack observations

Problems

Loose Wet

Friday and Saturday are forecasted to receive precipitation in the form of rain (particularly substantial rain amounts Saturday) Treeline and Below Treeline elevation bands will be subjected to additional loading and critical warming as a result of this weather event and we should see wet avalanches initiate on steep unsupported terrain as a result. Location: Widespread on all aspects and at all elevations. Possibility of triggering: During warming and rain events it is very likely to certain that human will trigger this problem and natural avalanches are likely to very likely. Size: If triggered expect these avalanche to be small but will entrain and could become large up to size 2 with enough mass to bury injure or kill a mountain traveler. In isolated terrain features very large avalanches size 3 are possible.

Likelihood

Possible

Expected Size

1 - 1

Persistent Slabs

A layer of facets 20cm thick can be found down nearly a meter in the snowpack. Currently isolated testing of this layer is not producing results. This persistent layer is a concern because when it is trigger consequences will be severe. The likelihood may be low but the consequences are high, continual loading of the snowpack from numerous past storm systems is likely to increase the magnitude and perhaps reach a tipping point where sensitivity to triggering increases. Location: Isolated sheltered large terrain features but found on all aspects in both the Alpine and at Tree line. Possibility of triggering: Unlikely to Possible to both natural and human triggers. Size: If triggered expect these avalanches to be large to very large size 2 to 3.

Likelihood

Possible

Expected Size

1 - 1

Wind Slabs

Found on predominantly North aspects, this avalanche problem overlies a variety of surfaces that include below 1500 meters a crust and above this elevation old storm snow. Expect that this problem will still exist, but is beginning to settle and bond with forecast cooling temperatures. Location: North aspects and found in both the Alpine and at Tree line specific to terrain just below ridge top. Possibility: Triggering of this avalanche problem is possible to likely from light loads such as skiers. Natural avalanches are unlikely to possible. Size: If triggered expect these avalanches to be small, and on isolated terrain features large, size 2.

Likelihood

Possible

Expected Size

1 - 1

Valid until: Jan 16th, 2021 1:00AM