Avalanche Forecast
Issued: Jan 31st, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
rbuhler,
Avalanche Canada
Recently formed wind slabs are expected to remain touchy on Tuesday, especially where they overlie surface hoar or a crust. Loose dry avalanches should be expected on steep slopes.
Summary
Confidence
Weather Forecast
Unsettled conditions are expected on Tuesday as Arctic air shifts southward.
Monday Night: Partly cloudy, light to moderate NW wind, treeline temperature dropping to around -12 C°.
Tuesday: Periods of snow flurries up to 5 cm and sunny breaks both expected, light to moderate NW wind, treeline high around -8 C°.
Wednesday: A mix of sun and cloud, light variable wind, treeline high around -14 C°.
Thursday: A mix of sun and cloud, light to moderate variable wind, treeline high around -10 C°.
Avalanche Summary
On Sunday, small loose dry avalanches were reported from very steep terrain. On Saturday, a skier triggered a size 1.5 wind slab on an E aspect in the alpine which failed down 5-20 cm.
Avalanche activity on the early-December weak layer described in the snowpack summary has been sporadic over the past few weeks. Prior to this most recent drought, we were tending to see reports of avalanches on this layer every few days. Most of the avalanches occurred at elevations around 2000 m. Possible natural triggers include daytime warming, warming from the sun, cornice falls, or smaller avalanches stepping down. Human triggering is most likely in steep, rocky slopes with a shallow or thin-to-thick snowpack.
Snowpack Summary
Up to 20 cm of new snow has buried a highly variable snow surface which consists of wind affected surfaces in exposed high elevation terrain, a melt freeze crust at lower elevations and on solar aspects extending into the alpine, and/or widespread surface hoar in sheltered areas which was typically 5-15 mm.
A layer of surface hoar buried around January 24 is now down 30-40 cm. While this layer was not creating a problem prior to storm, it is yet to be determined how it will react to the additional snowfall. A crust and surface hoar interface buried around January 11 is now down around 50-60 cm.
The most notable layer of concern in the snowpack is a facet/crust layer that formed in early December and ranges in depth between 80 cm along the shallower eastern Purcells and up to 150 cm in the western Purcells. This recent blog post goes into more details on this interface and why it is expected to continue to create problems for the rest of the season.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
- Conditions may have improved, but be mindful that deep instabilities are still present.
Problems
Wind Slabs
The new snow is expected to be most reactive in wind loaded terrain, especially where it overlies surface hoar and/or a crust. The wind was recently blowing from the SW during the storm but has now shifted to the NW so wind slabs should be expected on most aspects.
Aspects: North, North East, East, South East, South, South West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A concerning weak layer of faceted grains above a melt-freeze crust is around 70 to 150 cm deep. We had been receiving reports of large, destructive avalanches on this layer every few days. We've been reminded multiple times over the last month that this layer could remain a concern all winter. Thin rocky start zones are the most likely place to trigger this layer. Snow loading from new snow and/or wind, daytime warming, cornice falls, and step-downs from smaller avalanches could increase the chance of an avalanche on this layer. Learn more about this crust and how to deal with it in this forecasters' blog.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 1st, 2022 4:00PM
