Avalanche Forecast
Issued: Feb 24th, 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.
jleblanc,
Avalanche Canada
Yellow means caution ! Wind slabs are still reactive to human triggering on all aspects, and buried surface hoar layers remain suspicious on open slopes. Make sure to read the section Avalanche Problems.
Summary
Confidence
Weather Forecast
A strong ridge of high pressure will keep the region dry and cold until the weekend, with the potential for lingering valley clouds and an alpine temperature inversion. The next storm is expected late Sunday night as a shift in the weather pattern will occur.
Thursday night: Clear skies. Alpine temperatures around -15 C. Light to moderate northerly winds.
Friday: Mainly clear. Lingering valley cloud. Alpine temperatures around -10 C. Light to moderate northwesterly winds.
Saturday: Increasing cloudiness. Flurries up to 5 cm in the afternoon. Freezing level rising to 800 m. Alpine temperatures around -8 C. Light to moderate southwesterly winds.
Sunday: Snow 5-10 cm. Freezing level rising to 1100 m. Alpine temperatures around -4 C. Moderate to strong southwesterly winds.
Avalanche Summary
Wednesday, in the Monashees, a skier accidentally triggered a large wind slab avalanche (size 1.5) on a steep treeline feature on a slope previously skied by 7 persons. Earlier this week, shifting arctic winds have redistributed the storm snow into wind slabs and a natural avalanche cycle occurred on southerly aspects.
Persistent slabs were also observed lately, such as two large avalanches (size 3) reported near London Ridge and in the Valhallas. They both occurred naturally on south-westerly alpine slopes. This evidence is showing that, with added load to the snowpack from the last weekend’s storm, the mid-January weak layer began to "wake up".
Snowpack Summary
Last weekend's storm brought 20-80 cm of new snow accompanied by southwesterly winds. The north of the region received highest snowfall amounts, with tapering amounts to the south. Recent northeasterly has created a heavily wind-affected surface in exposed areas and redistributed storm snow into wind slabs in lee areas. Below ~1200 m the majority of the precipitation fell as rain, with 10-20 cm of snow now overlying a thick melt-freeze crust.
Up to 80 cm now overlies a weak layer formed in mid-February. This layer is comprised of surface hoar in sheltered areas, a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. Reports suggest that in many areas, the storm snow is bonding poorly to this firm layer.
The mid-January surface hoar/crust layer is now down 50-150 cm in the snowpack. This layer has started to 'wake up' following last weekend's snowfall.
Terrain and Travel
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Keep your guard up at lower elevations. Wind slab formation has been extensive.
- Use small low consequence slopes to test the bond of the new snow.
- Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
Problems
Wind Slabs
Wind slabs exist on various aspects in any exposed terrain and around ridgelines. Shifting winds (initially from the southwest, then switching to the northeast) are 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: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
There are two prominent weak layers in the upper meter of the snowpack.
An upper layer exists down ~30-70 cm and is comprised of surface hoar in sheltered areas, a crust at lower elevations and on solar aspects, and hard wind-affected snow in the alpine and exposed treeline. Reports suggest that storm snow is bonding poorly to this hard interface in many areas, and reactivity on this layer may persist. Be particularly cautious in sheltered areas where surface hoar may be preserved, or south-facing aspects where recent wind-loading has occurred and a sun crust may be buried.
The lower layer may be found roughly a meter deep in the snowpack. This layer consists of faceted snow, a sun crust on steep solar aspect, and most notably large surface hoar crystals in sheltered terrain. Over the past few weeks, reactivity on this layer had tapered, but the storm over the weekend caused this layer to 'wake up' on northerly aspects around treeline. The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks, and on steep convexities. Terrain features to be suspect of include the lee side of ridges, openings in trees, cut blocks, and burns, especially on northerly aspects where the layer may not be capped by a firm crust.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 25th, 2022 4:00PM
