Avalanche Forecast
Issued: Jan 17th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Deep Persistent Slabs.
cgarritty,
Avalanche Canada
Forecast snowfall for Saturday's storm varies across the region, and it's not a clear cut split between north and south. Expect avalanche danger to increase over the day as new snow accumulates and is affected by wind.
Summary
Confidence
Low - Forecast snowfall amounts are uncertain.
Weather Forecast
Friday night: Cloudy with increasing flurries bringing about 5 cm of new snow by morning. Light to moderate south or southwest winds, increasing.
Saturday: Cloudy with flurries or snow showers bringing a variable 10-25 cm of new snow, easing overnight in most areas. Moderate to strong south winds. Alpine high temperatures around -5, closer to -3 in the south of the region.
Sunday: A mix of sun and cloud with isolated flurries and a trace of new snow, increasing overnight. Light to moderate south winds. Alpine high temperatures around -3, closer to 0 in the south of the region.
Monday: Cloudy with scattered flurries bringing a trace to 5 cm of new snow. Light south winds. Alpine temperatures around -3, closer to 0 in the south of the region.
Avalanche Summary
A report from Thursday in the McGillivray pass area in the north of the region included observations of several storm slabs reaching size 2.5 (large) releasing naturally from steep north aspects in the alpine during a period of intense snowfall.
Reports from the region have been limited during the recent cold snap, however a MIN from Tuesday describes winds actively forming new slabs in the Duffey area. Similar conditions were observed in the Coquihalla area:
Last Saturday, a few explosives-triggered avalanches in the north of the region stepped down to the Christmas surface hoar layer mentioned in our snowpack summary, buried 50-60 cm deep at the time.
Two Thursdays ago, explosive control work produced a size 2 avalanche off the Duffey Lake road that released on the mid November facet/crust layer.
Snowpack Summary
A variable 15-30 cm of new snow is expected to accumulate over the region by the end of the day on Saturday. This will bury recent wind slabs and wind-affected surfaces in exposed areas at all elevations and soft, low density snow in sheltered areas.
90-150 cm of snow currently sits above a weak layer of surface hoar from Christmas that professionals are tracking in the north of the region. It may be found at treeline and below on shaded aspects in sheltered areas.Â
A deep persistent weak layer remains a serious concern at the bottom of the snowpack in the northern half of the region (e.g., Duffey, Hurley). It's made up of sugary faceted grains and a hard melt-freeze crust. This layer is most likely to be triggered in thin, rocky features where it exists closer to triggering forces on the surface.
Concern for very large avalanches releasing over this weak basal layer will increase in areas of the north where loading from new snow, wind, and rising temperatures strain the snowpack and cause avalanche activity in surface layers.
There are currently no concerns about deep weaknesses in the snowpack near Coquihalla summit and elsewhere in the south of the region.
Terrain and Travel
- Storm slab size and sensitivity to triggering will likely increase through the day.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
- Be alert to conditions that change with elevation and wind exposure.
Problems
Storm Slabs
Forecast snowfall for Saturday's storm varies considerably across the region, and it's not a clear cut split between north and south. In areas where less than 15 cm of new snow accumulates, anticipate fresh wind slabs to form in leeward terrain. In areas that see more, a more widespread storm slab problem may emerge by the end of the day.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
Two layers that cause concern in the northern part of the region include:
- A 90-150 cm-deep weak layer of surface hoar layer found around treeline elevations in sheltered areas. It may still be triggered by a person in steep, sheltered openings around treeline.
- A weak layer buried near the bottom of the snowpack which continues to produce sporadic very large avalanches. This layer is most likely to be triggered in steep, thin, rocky areas in the alpine or upper treeline.
Loading from new snow and avalanches in surface snow layers may test these layers over the weekend.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 18th, 2020 5:00PM
