Avalanche Forecast
Issued: Dec 28th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
jpercival,
Avalanche Canada
Keep it simple for now, patience is required as a warm and wet snowpack needs time to cool and bond. Seek simple terrain to assess the snowpack prior to beginning your journey into more challenging zones.
New snowfall and wind will continue to add weight to a weak snowpack where buried weak layers are primed for human triggering.
Summary
Confidence
Moderate
Avalanche Summary
Both Monday and Tuesday have been action packed with with many professional operations reporting that a natural avalanche cycle was occurring, these slab avalanche were reported as large to very large (size 2.5 to 3) . Further evidence of cracking and settling of the warm and moist upper snowpack provided good evidence of the new storm snow instability. Explosives work conducted on Monday and Tuesday produced some large (size 2) avalanches that gained mass with the available moist snow.
On Sunday. In the alpine numerous remotely trigger very large avalanches (size 2.5) have been reported. These were described as failing on the December 22nd facet interface/ Persistent weak layer on north east aspects with crown depths averaging 40 cm and gaining significant mass and running far, upwards of 400 meters in length.
Past avalanche activity Friday reported several remote avalanches that were large (size 2). Wind loaded features stepped down to a persistent slab, failing on the December 22nd, December 17th or November 21st layers.
Read about their decision making after triggering the first avalanche here.
Snowpack Summary
Tuesdays storm snow of 16 cm continues to bury a thin melt freeze crust that formed Monday, it can now be found down 40 cm. Wind and storm slabs have accumulated over layers of either facets, surface hoar or a crust. Strong westerly winds have been redistributing snow into wind loaded features in treeline and alpine terrain.
The snowpack is complex with several deeper instabilities that may persist through the season, and sustained past cold temperatures that had continued to facet (weaken) the snowpack. Layers of concern in this snowpack:
An early December layer of surface hoar in sheltered areas and a thin sun crust in open south-facing terrain is buried approximately 60-75 cm deep. This layer has recently produced surprising avalanches in upper treeline and lower alpine terrain features.
The most concerning layer buried in mid November is made up of large surface hoar crystals, facets, and a melt-freeze crust and can be found up to 70 to 120 cm deep. This layer has been reactive at treeline between 1700 to 2200 m, on all aspects.
Weather Summary
Wednesday Night
Cloudy with some clearing, snowfall; 1 to 5 cm. Moderate northwest winds 30 to 40 km/h. Freezing levels descending to 200 m. Alpine temperatures -6°C
Thursday
Cloudy, snowfall very light; 1 to 2 cm. Moderate to strong south wind 40 to 50 km/h. Freezing levels will maintain around 500 m Alpine temperature high of -4°C
Friday
Cloudy, snowfall; light 1 to 5 cm. Moderate southwest winds 20 to 30 km/h. Freezing levels rising mid day to near 1000 m. Alpine temperature high of -2°C.
Saturday
Snowfall, light 1 to 4 cm. Light southwest winds 20 to 30 km/h. Freezing levels 200 m. Alpine temperatures -6°C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
Problems
Storm Slabs
Storm totals have reached 40 cm in some areas. Expect reactivity as storm slabs sit over a variety of weak surfaces - facets, a crust and/or surface hoar.
Expect winds to have redistributed snow at treeline and alpine elevations into deeper and more reactive slabs in wind loaded features.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
There are three persistent weak layers of concern buried in the snowpack, see the Snowpack Summary for more details.
Layers of surface hoar can be found in shaded and wind sheltered terrain features primarily at treeline and low alpine elevations, while crusts can be found on sun affected slopes. These layers are most concerning on large open slopes where wide propagation could produce large avalanches.
Small avalanches have the potential to step down to these deeper layers. As snowfall accumulates, these layers are expected to become reactive to human triggers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 29th, 2022 4:00PM
