Avalanche Forecast
Issued: Dec 1st, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs.
dsaly,
Avalanche Canada
A reactive layer of surface hoar below the recent snow is primmed for human triggering. Choose conservative terrain and give the young snowpack time to bond and grow.
Summary
Confidence
Low
Avalanche Summary
On Wednesday, MINs reported touchy cut banks (MIN1), whumpfing and shooting cracks (MIN2) and reactive snowpack tests (MIN3). These reports covered a reactive layer of surface hoar below up to 40 cm of new snow, however, MIN3 also found another reactive layer of surface hoar down 75 cm. For now, we lack field observations to determine the distribution of this layer, but it is something we will be tracking.
Earlier in the week (Sunday-Monday), a few small (size 1) avalanches were reported south of Nelson. There were also reports of whumpfing and cracking suggesting the recent snow is poorly bonded to the mid-November weak layer.
Snowpack Summary
Overnight snowfall accumulations ranged from 15-25 cm by Thursday morning, and upwards of 40 cm has accumulated in the last few days. In the short term, reports suggest the new snow is not bonding to a layer of surface hoar below.
Early season conditions exist with low snow amounts and under snow hazards existing at lower elevations and a deeper and drier snowpack exceeding 1 m at treeline and alpine elevations. In wind-loaded areas, snowpack heights have been reported as deep as 160 cm with windward areas scoured down to as little as 20 cm.
Up to 75 cm of snow overlies a weak layer that formed mid-November that consists of sugary faceted grains, weak surface hoar crystals in sheltered terrain features, and a hard crust on steep sun-exposed slopes. This MIN reports moderate sudden collapse results when testing this interface.
Weather Summary
Thursday night
Cloudy with isolated flurries with trace accumulation. 10-20 km/h west wind, treeline temperatures fall below -18 °C.
Friday
Increasing clouds through the day with light flurries starting late in the afternoon. Increasing southwest wind 10-20 with gusts to 30 km/hr. Treeline temperature high -9 °C.
SaturdayGusty winds and scattered flurries overnight, 5-10 cm accumulating by Saturday morning. Southwest wind 20-35 km/hr decreasing through the day. Treeline high temperature -5 °C.
SundayClear, cold, and calm. Light northeast wind, treeline temperatures falling to -12 °C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Remote triggering is a concern, watch out for adjacent and overhead slopes.
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
Problems
Storm Slabs
Reports suggest the recent 20-40 cm is poorly bonded to the interface below (a layer of surface hoar) and has been reactive to skier traffic. Keep an eye on the wind, slabs may quickly form wherever the wind encourages the fresh snow to bond; and with a weak layer of surface hoar below, reactive slabs may be more widespread and extend into treeline elevations and be more reactive than expected in sheltered areas.
The "upper" early winter snowpack consists of around 70 cm of recent snow over various layers formed mid-November, including surface hoar, faceted grains, and a hard crust. While our avalanche concern is focused on the interface just below the recent snow, we're hoping to gain more information on the distribution and sensitivity of these deeper layers as we collect more field observations.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 2nd, 2022 4:00PM
