Avalanche Forecast

Archived

Feb 3rd, 2024–Feb 4th, 2024

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Purcells, Dogtooth, East Purcell, West Purcell, Bull.

Small but reactive wind slabs may form as storm snow accumulates on eastern slopes.

Continue to avoid large and consequential terrain while the snowpack cools and strengthens.

Confidence

Moderate

Avalanche Summary

We expect wind slab avalanche activity to increase on Sunday with cooler temperatures and fresh snowfall.

Snowpack Summary

By Sunday afternoon storm totals are expected to reach 10 in most areas, with hotspots of up to 20 cm possible on the eastern slopes of the Purcells. This snow accumulates over a crust that varies in thickness and elevation throughout this forecast area. In the Dogtooth Range, this crust thins into the alpine and becomes breakable.

The top 50 cm of snow at treeline is moist with several layers of crusts and facets below. At the base of the snowpack, weak faceted grains and depth hoar is present. While cooler temperatures are expected to help these layers to strengthen we continue to monitor them for signs of reactivity.

Weather Summary

Saturday Night

Cloudy with up to 15 cm of new snow expected, favoring the eastern slopes of the Purcells. Northeast winds 10-30 km/h. Freezing levels around 1500 m, treeline temperatures near -4 °C.

Sunday

Mostly cloudy with up to 5 cm of new snow expected. Freezing levels around 1000 m, treeline temperatures around -8 °C. Easterly winds ease, 10-20 km/h.

Monday

Mostly cloudy with possible flurries. Freezing levels reach 1000 m, treeline temperatures around -8 °C. Southerly winds 10-20 km/h.

Tuesday

Mostly cloudy with possible flurries. Freezing levels reach 1300 m, treeline temperatures around -6 °C Southerly winds 10-20 km/h.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.