Avalanche Forecast
Issued: Dec 15th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
rbuhler,
Avalanche Canada
New wind slab formation is expected on Thursday as the wind shifts to a northwest direction. Given the recent shifting wind directions, reactive slabs should be expected on all aspects in exposed terrain.
Summary
Confidence
Weather Forecast
Arctic high pressure remains for Thursday but the wind is expected to shift to a NW direction. Unsettled conditions are expected for Friday in advance of a relatively weak Pacific storm system which is currently forecast to impact the region on Friday night and Saturday.
Wednesday Overnight: Mainly clear, moderate to strong NW winds, treeline temperature around -16 °C.
Thursday: Mostly sunny, moderate to strong NW winds, treeline high around -14 °C.
Friday: Increasing cloud cover, winds becoming moderate SW, treeline high around -14 °C.
Friday Night and Saturday: Light to moderate snowfall, moderate to strong SW winds, treeline high around -12 °C.
Avalanche Summary
On Tuesday, natural wind slabs to size 2 were reported in the north of the region. In the south, explosives were triggering wind slabs to size 2. This MIN report highlights the wind slab problem around Terrace.
On Thursday, wind slabs are expected to remain the primary concern in the region. The wind slabs which formed on Monday and Tuesday from NE outflow winds are expected to remain reactive to human triggering. New wind slab formation is also expected as the winds become strong from the NW. Reactive wind slabs should be expected on all aspects in exposed terrain.
The persistent slab problem appears to generally have stabilized in the south of the region but remains a concern in the north. We are now likely in a low probability/high consequence scenario with the persistent problem.
Snowpack Summary
Over the weekend, the region typically saw 20-50 cm of new snow with the greatest amounts towards the SW of the region. This new snow was accompanied by strong SW winds had formed reactive wind slabs in exposed terrain. On Monday and Tuesday, strong outflow (NE-E) winds formed new wind slabs on South and West aspects. On Thursday, the wind is expected to shift to the NW so new wind slab formation is expected where there is still unconsolidated surface snow available for transport.
The December 7 persistent weak layer is now typically down 40-70 cm except for near the immediate coast where it is closer to 100 cm. This interface may include a crust, facets, and/or surface hoar. This layer appears to be gaining strength through the south of the region but remains a concern for the north of the region. A bit deeper in the snowpack is the December 1 crust/facet layer which generally appears to have stabilized but may still be reactive in isolated areas.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Be aware of the potential for large avalanches due to the presence of buried weak layers.
Problems
Wind Slabs
New wind slab formation is expected on Thursday resulting from forecast strong winds from the NW. Older wind slabs from the strong outflow winds on Monday and Tuesday also remain a concern, especially on south and west aspects. Given the shifting nature of the recent winds, wind slabs should be expected on all aspects in exposed terrain.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
There is still concern for persistent weak layers like facets and surface hoar which may rest on the crust which was buried last week and is now typically down 40 to 70 cm below the surface. This interface appears to have stabilized in the south of the region but remains a concern in the north.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 16th, 2021 4:00PM
