South Rockies

Watch for changing conditions with arrival of Sunday's new snow and Strong wind. Be alert for signs of instability - especially if you encounter new snow accumulations of over 10 cm OR signs of fresh wind loading under foot / snowmobile.    

Saturday Night: Cloudy with clear periods. Trace Accumulations. Moderate to Strong West winds (20-40km/hr). Freezing level will drop to valleys. Alpine Low -10 C.  

Sunday: Increasing Clouds with Snow and wind arriving mid-day. Total accumulations of 3-10 cm. Moderate Southwest winds (20 km/hr) becoming Strong (50-60 km/hr) by days end. Alpine High -2 C with Freezing Levels rising to 1500m.

Monday: A mix of Sun and Clouds with scattered flurries. 3-8 cm of new snow. Winds diminishing Light to Moderate (15-30 km/h) from the West/Northwest. Alpine Highs around -8 / Low -12 with Freezing Level 1000m.   

Tuesday: Cloudy with continued snow flurries in the early morning and mix of sun and clouds by afternoon. Trace to 5 cm new snow. Winds Moderate (20-35 km /h) from the West / Northwest. Alpine Highs around -6 / Low -13 with Freezing Level 1200m.  

No notable avalanche activity was reported in the region since Tuesday. We forecast this to change with Strong winds and the arrival of new snow on Sunday. These winds will continue to build cornices, as illustrated in this MIN. 

Natural large (size 2) slab avalanches were observed Sunday, Monday and Tuesday. These included natural failures on the Feb rain crust, Cornice triggered slopes, thin wind slabs stepping down to the early Feb rain crust in a fan, or below steep rocky faces such as in this MIN at Window Mountain. 

There have been no reports of deep persistent slab activity on the basal weak layers for over a week. The most recent is described in this MIN report from February 11 and this MIN report on February 9th. This layer may become reactive with a large trigger, such as a natural Cornice or step down from a small avalanche particularly in shallow rocky start zones.

Highest precipitation rates of snow are forecast to arrive on Sunday afternoon and into the night. Even small amounts of new snow earlier in the day combined with Strong winds can lead to the development of wind slabs in the Alpine, the immediate lee of Ridgetop and on cross loaded features at treeline and below.  

New snow will fall on a variety of snow surfaces: melt freeze and sun crusts on steep solar aspects, scoured slopes on windward sides of alpine and near treeline, soft faceted snow in sheltered areas and wind slabs in immediate lees of ridge crests.  

A thick rain crust sits 30-60 cm below the surface and can be found up to 2100 m. Recent avalanche activity has been observed at the faceting interface between this crust and overlying snow.

A well consolidated and settled mid-pack overlies generally weak basal facets that are most prominent in shallow rocky start zones.

• Wind slabs are most reactive during their formation.
• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.