Avalanche Forecast
Issued: Feb 21st, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Cornices and Persistent Slabs.
zryan,
Avalanche Canada
Continue to make conservative terrain choices as northerly outflow winds form fresh reactive wind slabs in lee areas.
A more widespread storm slab problem may persist in the south of the region, where greatest snowfall amounts were received.
Summary
Confidence
Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.
Weather Forecast
Bundle up in your warmest gear, arctic air is here!Â
Monday Overnight: Clear skies. Alpine temperatures around -25 C. Moderate to strong northeasterly winds.Â
Tuesday: Cold and clear. An alpine high of -20 C. Moderate to strong northeasterly outflow winds at all elevations, easing in the afternoon.
Wednesday: Mainly cloudy with light snowfall. Winds shifting northwest and strengthening strong to extreme. Alpine temperatures rising to -15 C.
Thursday: Partially cloudy, light flurries. Light to moderate northwest winds. Alpine temperatures around -15 C.
Avalanche Summary
In the Pine Pass area on Monday, a snowmobile-triggered wind slab was observed on a north aspect, which is suspected to have occurred over the weekend. A natural wind slab was also observed on a south aspect, likely within a similar time frame.
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.Â
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.Â
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.Â
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
Storm Slabs
Throughout the day today, northeasterly outflow winds may cause reverse loading, transporting available snow into fresh wind slabs in normally wind-scoured slopes.
With greater snowfall amount in the south, we can expect a more widespread storm slab problem to persist. 40-100cm of recent storm snow may bond poorly to the underlying hard melt-freeze crust. Dry-loose avalanches may be seen from steeper slopes, especially where a firm crust exists below the new snow.
In the north of the region, the problem is likely more confined to a wind slab problem. 10-30 cm of recent storm snow has been redistributed into pockets of wind slab in lee areas.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Cornices
Cornices may have grown significantly with wind and snowfall over the weekend. Be especially mindful of overhead cornice hazard if the sun comes out and the storm snow is experiencing strong solar radiation for the first time.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
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 22nd, 2022 4:00PM
