Avalanche Forecast
Issued: Dec 19th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Storm Slabs.
ghelgeson,
Avalanche Canada
The forecast calls for 15 to 25 cm of storm snow and strong wind Saturday night which is likely to initiate a natural avalanche cycle across the region. Human triggered avalanches are likely Sunday, especially in wind exposed terrain.
Summary
Confidence
Low - Uncertainty is due to the limited number of field observations.
Weather Forecast
One last pulse of storms Saturday night into Sunday before a clearing trend takes hold for the work week.
SATURDAY NIGHT: Freezing level around 1000 m, strong southwest wind, 15 to 25 cm of snow expected.
SUNDAY: Freezing level near valley bottom, broken cloud cover, strong west/northwest wind, 5 to 10 cm expected through the day.
MONDAY: Broken cloud cover, freezing level at valley bottom, light northerly wind, trace of snow possible.
TUESDAY: Scattered cloud cover, freezing level at valley bottom, light northerly wind, no precipitation expected.
Avalanche Summary
A significant amount of new snow and wind are expected to lead to a natural avalanche cycle Saturday night that may extend in Sunday.
On Saturday, near Valemount, avalanches to size 1.5 were observed on a northeast facing feature at treeline, more details here. A very similar observation was reported in Allen Creek Friday.
Snowmobilers remotely triggered a storm slab over surface hoar Wednesday near Allen Creek (MIN report).
Several large natural avalanches were reported last Friday at Chappel Creek (see this MIN report). These avalanches occurred on south aspects at treeline elevations. Based on the depth of these avalanches, they likely failed on recently buried surface hoar and/or sun crust layers.Â
Snowpack Summary
Incremental loading has stacked 30 to 65 cm of low density snow around the region. Areas to the east around Blue River have received the higher numbers. Southwest winds have built slabs in lee features at upper elevations.
A weak layer of surface hoar that was buried about a week ago is now down 40-60 cm. In many areas the weak layer exists as a crust, and in other areas, surface hoar. The bond at this interface is poor, slabs will become increasingly reactive as fresh snow gains cohesion and slab properties.
Near the base of the snowpack is a crust that was buried in early November. This crust likely has weak facets associated with it. There have been no recent avalanches reported on this layer, though it may be possible to trigger from shallow, rocky terrain.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
- Make conservative terrain choices and avoid overhead hazard.
- Avoid freshly wind loaded terrain features.
- Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
Problems
Persistent Slabs
This storm may well push the persistent slab over the tipping point resulting in large and surprisingly touchy slab avalanches. The slab rests on a persistent weak layer which has the capacity to propagate avalanches across terrain features. Wind exposed features are expected to be particularly volatile.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Storm Slabs
Look for the formation of fresh, sensitive storm slabs as strong southwest wind and 15 to 25 cm of new snow come together Saturday night into Sunday.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 20th, 2020 4:00PM
