Avalanche Forecast
Issued: Dec 26th, 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
Heavy snowfall, wind and warm temperatures have added to a weak snowpack where buried weak layers are primed for human triggering.
Summary
Confidence
Avalanche Summary
A dramatic increase in avalanche activity was reported during 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
The recent storm snow has warmed and become dense, forming slab like properties These wind and storm slabs have accumulated over layers of either facets, surface hoar or a crust. Westerly winds are redistributing snow into wind loaded features in treeline and alpine terrain.
The snowpack is becoming increasingly complex with several deeper instabilities that may persist through the season, and sustained past cold temperatures had continued to facet (weaken) the snowpack. Layers of concern in this snowpack:
The latest snowfall sits on a surface hoar layer from late December. Recent reports indicate the storm snow is very sensitive to human and remote triggers.
An early December layer of surface hoar in sheltered areas and a thin sun crust in open south-facing terrain is buried approximately 30-50 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 80 cm deep. This layer has been reactive at treeline between 1700 to 2200 m, on all aspects.
Weather Summary
Monday Night
Heavy snowfall will continue with 10-15 cm expected overnight. Sustained moderate southwesterly wind 40 to 60 km/h . Alpine temperatures warming to or above -4°C as freezing levels maintain at 500 m.
Tuesday
Snowfall, heavy at times 15 to 30 cm. Freezing levels climb to 1500 m for a brief period near the end of the day. Moderate to strong southwest winds 60 to 70 km/h. At terrain below 1500m a potential for rain on snow is possible.
Wednesday
Snowfall, moderate 10 to 15 cm. Freezing levels will descend to near valley bottom by days end Moderate to light north winds 20 to 30 km/h.
Thursday
Snowfall, light with trace amounts. Freezing levels near valley bottom. Light southwest winds 20 to 30 km/h.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Use increased caution at all elevations. Storm snow is forming touchy slabs.
- 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 reach 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 27th, 2022 4:00PM
