Avalanche Forecast
Issued: Jan 9th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
JSmith,
Avalanche Canada
New snow and extreme winds will form widespread storm slabs reactive to human triggers. Hazard may rise rapidly to HIGH in areas that receive more than 20 cm of new snow.
Summary
Confidence
Weather Forecast
SATURDAY NIGHT: Snow; 10-20 cm. / Extreme, south ridgetop wind / alpine low temperature -8 / Freezing level 400 m.
SUNDAY: Snow; 10-15 cm, with another 20-30 cm. overnight / Extreme, south ridgetop wind / alpine high temperature -3 / Freezing level 1000 m.
MONDAY: Snow; 10-15 cm. / Strong, southwest ridgetop wind / alpine high temperature -5 / Freezing level 800 m.
TUESDAY: Snow; 15-20 cm. / Extreme, south ridgetop wind / alpine high temperature -4 / Freezing level 900 m.
Avalanche Summary
A few naturally triggered wind slabs up to size 2 continue to be reported. Additionally, there have been numerous recent reports of "whumphing" (collapsing) on a weak layer of surface hoar down around 100 cm. See recent MIN reports HERE.
Avalanche activity is expected to increase on Sunday as new snow and strong winds build fresh storm slabs.
Snowpack Summary
A non-stop series of storms has deposited 75 to 150 cm of new snow since New Year's. The amount of snow, as well as the wind speed and direction, has been highly variable between different drainages over this period, so there is uncertainty about exactly what the upper snowpack will look like as we come out of this storm. However lingering storm and wind slabs will likely need a few days to stabilize.
Aside from this new snow, the main concerns vary throughout the region. In the Shames area, this new snow has been bonding poorly to a surface hoar and crust layer that is now an estimated 75-125 cm deep. A bit further north in the Nass/Sterling/Beaupre areas there is potentially still concern about an older weak layer of surface hoar and crust that is now roughly 150 cm deep. In the far north of the region there is concern about weak snow at the bottom of the snowpack. At this point there is some uncertainty about whether these layers will still be reactive after such an intense stormy period.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
- Watch for rapidly changing conditions during periods of heavy loading from new snow, wind, or rain.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
Problems
Storm Slabs
New snow and extreme winds will form widespread storm slabs reactive to human triggers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
New snow and extreme winds may overload deeply buried weak layers, resulting in very large avalanches. In the Shames area the main concern is a layer of surface hoar 75-125 cm below the surface, while further north there are deeper layers that pose a low likelihood, high consequence scenario. Choosing conservative terrain away from overhead hazard is the best way to manage this problem.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 10th, 2021 4:00PM
