Regions
Banff Yoho Kootenay.
Warm temperatures today have moistened the surface of the snowpack, and we expect this will have contributed to increased slab formation. The snowpack will remain tricky this week with continued light snow and warm temperatures.
Weather Forecast
A SW flow continues across BC and Alberta bringing continues precipitation and warm temperatures this week. Expect another 5cm on Tuesday, but up to 20cm by the end of the week. Temperatures on Tuesday will reach 0 degrees at treeline with freezing levels extending upwards to 2000m. Moderate winds overnight on Monday will calm down for Tuesday.
Snowpack Summary
10cm of soft surface snow became moist on Monday afternoon at lower elevations. This overlies a 40cm settled slab that produces sudden planar shears and is the main concern in the upper snowpack. Deeper in the snowpack, the facets from mid-December continue to plague us with sudden collapse test results in large, weak depth hoar grains.
Avalanche Summary
Size 2.5 avalanche ran over the ice climb, Rogan's Gully today (you could expect a similar occurrence on Cascade). Lake Louise and Sunshine ski areas reported 10-20 cm size 1 windslab avalanches from Sunday night's winds, and Lake Louise got one size 2 in the deep facets from an explosive in Elevator Shaft. Generally poor visibility today.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.