Avalanche Forecast

Issued: Jan 24th, 2019 4:50PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Deep Persistent Slabs and Wind Slabs.

cgarritty, Avalanche Canada

South Rockies.

We're entering a period of warming that may expose the weakness buried at the base of our snowpack. The possibility for large natural slab avalanches will increase with warmth and sun exposure.

Summary

Confidence

High -

Weather Forecast

Thursday night: Cloudy with clear periods and isolated flurries with a trace of new snow. Light southwest winds increasing to strong northwest in the alpine.Friday: A mix of sun and cloud. Moderate northwest winds increasing to strong in the alpine. Winds increasing overnight. Alpine high temperatures around -5.Saturday: Mainly sunny. Strong west winds reaching extreme in the alpine and increasing overnight. Alpine high temperatures around 0 to +1 as freezing levels jump to a possible 2500 metres.Sunday: A mix of sun and cloud with isolated flurries and a trace of new snow. Extreme northwest winds decreasing to moderate over the day. Alpine temperatures dropping from around 0 to -4 over the day as freezing levels decline from 2000 to 1000 metres.

Avalanche Summary

Wednesday's avalanche observations were limited to small (size 1), thin slabs released with ski cutting. Looking forward into a period of forecast warming, our primary concern is the potential for a relapse into conditions observed a couple of weeks ago when warm temperatures stressed the deeper layers in the snowpack and produced several large (size 2) natural deep persistent slab avalanches.

Snowpack Summary

Strong winds have redistributed snow into thin winds slab in alpine lees and scoured windward areas. In more sheltered alpine terrain and between 1600-2000 m, 5-15 cm of recent snow overlies a layer of weak surface hoar and crusts (on solar aspects). Large variability in snow depths still exists in the region, ranging from almost no snow to nearly 200 cm in some areas. For average snowpack areas, expect to find weak and sugary faceted snow around 50 to 100 cm deep, which extend to the ground. This weak bottom half of the snowpack has been the culprit for large avalanches in the region over the past few weeks.

Problems

Deep Persistent Slabs

Deeply buried weak layers are an increasing concern with substantial warming and sun in the forecast. These deep layers are more easily triggered in areas where the snowpack is shallow, such as near ridges and rocky terrain.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Avoid steep, rocky terrain and shallow snowpack areas where triggering is more likely.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Wind Slabs

Wind continues to redistribute loose snow into wind slabs at higher elevations. Expect to find the deepest and most reactive pockets in immediate lee areas near ridgecrests and around wind-exposed terrain features.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Be cautious on convex rolls around treeline where buried surface hoar may be preserved.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 1.5

Valid until: Jan 25th, 2019 2:00PM