Avalanche Forecast

Issued: Dec 28th, 2018 5:02PM

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

Avalanche Canada cgarritty, Avalanche Canada

Conditions will be prime for the rapid formation of touchy new storm slabs on Saturday. Manage your exposure by seeking out simple terrain and factoring in the possibility for storm slabs to step down to deeper layers.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Friday night: Cloudy with increasing flurries bringing about 15 cm of new snow by morning. Light to moderate south winds.Saturday: Cloudy with continuing snowfall bringing another 20-25 cm of new snow. Moderate to strong southwest winds, increasing over the day. Alpine high temperatures around -4 as freezing levels rise to 1500 metres.Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Mainly light northwest winds, easing over the day. Alpine high temperatures around -10Monday: A mix of sun and cloud. Light west winds. Alpine high temperatures around -13.

Avalanche Summary

Avalanche activity on Wednesday and Thursday was limited to a few small wind slabs, loose dry releases, and one large cornice pried out by explosive control work near ridgecrest. Monday was similar with riders triggering small loose dry avalanches in steep terrain as the storm snow sluffed away. The last reported persistent slab activity was on Sunday when a few large (size 3) persistent slab avalanches were observed on south facing alpine features. This was the final report from a widespread persistent slab avalanche cycle that was quite active last week, particularly in the Selkirks and the northern tip of the Monashees.Looking forward, increasing snowfall, wind, and freezing levels are setting up conditions ideal for the formation of storm slabs and natural avalanche activity. Although the likelihood of storm slabs 'stepping down' to deeper persistent slab problems is in question, travel plans should account for very large avalanches as the possible result.

Snowpack Summary

A building storm is now depositing new snow on the surface. Below the new snow, 10 to 20 cm of older low density snow sits above old wind slabs in the alpine, and in some isolated areas above small surface hoar (feathery crystals).A weak layer that formed during the dry spell in early December is now 80 to 120 cm deep. The layer is composed of weak facets, surface hoar, and a sun crust on steep south-facing slopes. This layer was previously responsible for large persistent slab avalanches, but activity has greatly diminished over the last week. Saturday's storm may breathe some life into it, the places of greatest concern will be north and east facing slopes between 1900-2300 m and steep south-facing slopes in the alpine.The lower snowpack is generally strong and settled, with a crust that formed in late October near the bottom of the snowpack.

Problems

Storm Slabs

An icon showing Storm Slabs
Heavy snowfall, increasing winds, and warming temperatures are brewing fresh storm slabs. The new snow is unlikely to bond well to the surface over the near term. Storm slab releases may also have potential to 'step down' to a deeper weak layer.
If triggered, storm slabs may step down to deeper layers and result in very large avalanches.Minimize exposure to avalanche terrain during periods of heavy loading from new snow and wind.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs
Avalanche activity at our deeply buried persistent weak layer has decreased, but new snow and wind will be adding load and testing this layer on Saturday. Steep south facing alpine features and convex terrain at treeline will be especially suspect.
Avoid exposure to overhead avalanche terrain during periods of heavy loading from new snow, wind.Revert to well supported, low consequence terrain as loading tests the strength of persistent slabs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Valid until: Dec 29th, 2018 2:00PM