Low hazard Below Treeline does not mean you can't be hit by a Large avalanche that started higher up. Minimize time in avalanche runout zones (these cross many Waterton trails). While not likely, any natural avalanches may reach runouts.
Weather Forecast
Saturday: Snowfall overnight, and in squalls throughout the day(5-15cm forecast). Ridge winds: Strong-Extreme SW. Freezing Level at valley floor. Treeline high -4.Sunday: Sun & cloud. W winds becoming light. Freezing Level at valley floor. Treeline Low -8, High -4.Monday: Mainly cloudy, flurries possible. Light winds. Treeline High -2.5
Snowpack Summary
A thick crust overlies a Moist snowpack Below Treeline. Wind exposed terrain is scoured and slick, but pockets of Wind Slab 5-30cm deep sit in sheltered lee terrain. These will grow with snow and wind forecast. A crust from Mid Feb, down 1m, is giving some sudden results in tests. The bottom of the snowpack is faceted, and still weak in places.
Avalanche Summary
On Friday, a small cornice fell into a steep lee slope at treeline. This triggered a relatively deep slab in the steep, rocky slope, which stepped down multiple times to deeply buried Persistent Weak Layers, and to Ground lower down. This ended up as a Large (Size 2.5) avalanche. No new avalanches were observed on Thursday with good visibility.
Confidence
Forecast snowfall amounts are uncertain on Saturday
Problems
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.
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.