New wind slabs may form overnight with light snowfall and moderate SW winds. The persistent weak layer from early February is gaining strength but don't write it off yet, large destructive avalanches may still be possible.
Summary
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Saturday
Weather Forecast
A weak storm front is expected to reach the region Friday night. 5-10cm of snowfall is expected by midday Saturday. Alpine winds are expected to be moderate from the southwest and freezing levels are forecast to be around 1600m. A weak ridge of high pressure should dry things out Saturday night. A mix of sun and cloud is expected for Sunday with light to moderate alpine winds from the southwest and freezing levels around 1500m. The second storm front is expected to arrive Sunday evening and another 5-10cm is forecast for the overnight period. Dry and mostly cloudy conditions are currently forecast for Monday.
Avalanche Summary
On Thursday, natural and skier triggered persistent slab avalanches were reported as well as large natural cornice releases and loose sluffing up to 2.5 on solar aspects. A skier triggered a size 2 slab on a northeast aspect convexity at 2150m which released on the February 21 surface hoar layer down 40cm. Two size 1 soft slab avalanches were reported from a northwest aspect which released down 20cm on a layer of surface hoar. A natural sluff triggered a size 2.5 slab avalanche on a south aspect at 2700m which released down 40cm. A cornice fall triggered a size 3 deep persistent slab on a northeast aspect around 2600m which was 1.5-2m deep but only observed from a distance. Another cornice fall triggered a size 3 slab on a northeast aspect at 2500m. On Wednesday, skiers triggered two size 2 persistent slab avalanches. One was on a northeast aspect at 1900m and released on surface hoar down 30-40cm that was buried on Feb 21. The other was on a northeast aspect at 1850m and released on surface hoar down 45cm that was buried on Feb 10. New winds slabs are expected to be the biggest concern on Saturday but deeper persistent layers may remain reactive in isolated areas.
Snowpack Summary
The new storm snow will bury a sun crust on south facing slopes and widespread surface hoar everywhere else. The surface hoar is being reported on all aspects and elevations up to 10mm except where it has been destroyed by the sun. New wind slabs are expected to form over the weekend with forecast moderate southwest winds in the alpine. A weak layer of surface hoar and/or a sun crust buried February 21 can be found 15-60cm below the surface. This layer is reported to be increasing in reactivity in the deeper snowfall areas as the week old storm snow continues to settle into a cohesive slab with recent warm temperatures. The surface hoar and/or crust layer which was buried February 10 is now down 60-100cm and has been responsible for some very large avalanches recently. This layer is expected to become much less reactive over the weekend with cooling temperatures. Large cornices have recently been a concern but should also gain strength will colder temperatures.
rbuhler,
Avalanche Canada
