Avalanche Forecast
Issued: Dec 20th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
ghelgeson,
Avalanche Canada
Saturday night's storm changed the game, and it's now time for very cautious mountain travel. The central and northern part of the region is primed for human triggered avalanches. More snow is on the way and conditions are not going to get better in the near term.
Summary
Confidence
Weather Forecast
The storm parade continues for the foreseeable future.
SUNDAY NIGHT: Freezing level lowering to near valley bottom, moderate west wind, trace of snow possible.
MONDAY: Broken cloud cover, freezing level near valley bottom, moderate southwest wind, 5 to 10 cm of snow expected during the day with potential for another 10 to 30 cm Monday night.
TUESDAY: Overcast, freezing level at valley bottom, light northerly wind, up to 5 cm of snow expected.
WEDNESDAY: Broken cloud cover, freezing level at valley bottom, light west wind, no new snow expected.
Avalanche Summary
Saturday nights storm almost certainly produced a natural avalanche cycle, the details of which should trickle in over the next few days.
On Friday and Saturday the buried surface hoar continued to show it's stuff making for touchy avalanche conditions which produced slabs to size 1.5, check out this great MIN report from the north of the region Saturday.
Natural wind slabs and cornice failures were reported on alpine features in the central portion of the region to size 1.5.
In the south of the region the snowpack is thin and there have reports of whumphing at ridgetop. Check out all of the MIN reports for the region here
Snowpack Summary
30 to 75 cm of storm snow has fallen recently with the deepest amounts being found in the north around Golden. Southwest winds have built slabs in lee features at upper elevations, reactive cornices have grown too.
Below the storm snow, the snowpack is a bit of a junk show. The early December surface hoar is down 30 to 80 cm below the surface now. On Saturday, before the big storm, it was sensitive to remote triggering which is well illustrated in this MIN post from the Golden area.
Below, or near the surface hoar you may encounter a crust. This crust can be bound as high as 2400 m in the south of the region and 1800 m in the north.
The lower snowpack is characterized by more crusts, the most notable is from a rain event in early November that is 50 to 130 cm deep. This crust is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers or in a step-down from a smaller avalanche in shallow, rocky areas.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
- Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
- Uncertainty is best managed through conservative terrain choices at this time.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Wind Slabs
Wind and new snow has continued to form reactive slabs which are most sensitive in wind exposed terrain. Where the new snow overlies surface hoar (or a crust) a poor bond has been noted. The problem is more likely found in northern parts of the region, in areas that have received the higher amounts of snowfall (e.g. Golden).
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A buried layer of surface hoar is now primed for human triggering. This layer is thought to be widespread and was quite sensitive to triggering before Saturday Night's big storm. This interface is capable of producing large to very large avalanches that are capable of connecting bigger pieces of terrain.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 21st, 2020 4:00PM
