Avalanche Forecast
Issued: Feb 22nd, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
zryan,
Avalanche Canada
Reverse loading from strong northeast winds has built wind slabs on unusual aspects, which could take riders by surprise.
Avoid wind-loaded terrain and continue to assess how recent storm snow is bonding to the underlying surface.
Summary
Confidence
Weather Forecast
A weak disturbance will come through on Wednesday with a light amount of snowfall expected in the region. The ridge of high pressure will reestablish on Thursday.
Tuesday Overnight: Increasing cloud cover. Winds shifting northwest and increasing moderate to strong. Alpine temperatures rising to around -15 C.
Wednesday: Cloudy with light snowfall. Moderate to strong northerly winds. Alpine temperatures around -15 C.
Thursday: Partially cloudy. Moderate to strong northwesterly winds. Alpine temperatures around -15 C.
Friday: Partially cloudy. Strong to extreme northwesterly winds. Alpine temperatures around -10 C.
Avalanche Summary
On Monday, in the Pine Pass area, the North Rockies Field Team observed evidence of recent wind slab avalanches. Check out their MIN report for more information
On Sunday, numerous dry loose avalanches were observed out of steep terrain in the McBride area.
Throughout the storm last weekend, limited observations have been made with poor visibility, but we expect a natural avalanche cycle occurred on Saturday. During the peak of the storm on Saturday, several large natural storm slab avalanches were reported from treeline elevations in the Kakwa.
Snowpack Summary
Last weekend's storm brought 20-100 cm of new snow to the region, with lightest amounts in the Pine Pass area, and heaviest amounts in the southwest ranges around McBride. This new snow overlies a widespread crust created from a rain event in early February. This 1-20 cm thick crust exists on all aspects and elevations, excluding areas in the high alpine in the south of the region that may remain crust-free.
Below the crust, 10-40cm of more settled snow exists above the late January weak layer. This layer consists of weak faceted snow, a melt-freeze crust, and surface hoar crystals in isolated sheltered areas at treeline and below. The surface hoar has been increasingly hard to identify in the snowpack and has shown no reactivity in the past week. In many areas, this layer is bridged by the thick crust above it.
The lower snowpack is generally strong and well-bonded. The base of the snowpack is expected to be weak and faceted in shallow, rocky slopes east of the divide.
Terrain and Travel
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Closely monitor how the new snow is bonding to the crust.
- Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
Problems
Wind Slabs
Wind slab will exist on various aspects in exposed terrain and around ridgelines. Last weekend's storm initially came in with southwest winds, but with the intrusion of arctic air, winds switched to the northeast, building slabs in less common locations.
These slabs may have formed on top of old crusts and hard wind-pressed snow and there is uncertainty about how quickly they will bond to old surfaces.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A weak layer formed by clear skies in late January exists in the upper meter of the snowpack. In most areas, a firm crust under the most recent storm snow will bridge the weak interface, making human triggering unlikely.
On the eastern side of the ranges in shallower snowpack areas, weak snow (basal facets) may exist near the base of the snowpack.
Large triggers, like warming, additional load from new snow, and cornice failures could be enough to wake these layers up, initiating large and surprising avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 23rd, 2022 4:00PM
