North Rockies

Stormy weather will create dangerous avalanche conditions on steep slopes that have been freshly loaded by new snow and wind.

A series of fronts hit the region Monday night, Tuesday night, and Thursday afternoon.

MONDAY NIGHT: Frontal system brings 10-15 cm of new snow to northern and eastern parts of the region (e.g. Pine Pass, Tumbler) and 15-30 cm to southern and western parts of the region (e.g. Torpy, Kakwa, Renshaw), strong to extreme wind from the west, freezing level dropping from 1000 m to valley bottom.

TUESDAY: Cloudy with isolated flurries and up to 5 cm of new snow, strong wind from the west, alpine high temperatures around -5 C.

WEDNESDAY: 5-15 cm of new snow by the morning then mix of sun and cloud in the afternoon, moderate wind from the southwest, alpine high temperatures around -8 C.

THURSDAY: Mix of sun and cloud with some light flurries in the afternoon, strong wind from the west, freezing level climbing from valley bottom to 1300 m in the afternoon, alpine high temperatures around -2 C.

Over the weekend a few small (size 1) human triggered slab avalanches were reported on north and east facing slopes (see photos in this Mountain Information Network report from a neighbouring part of the Cariboos). A few naturally triggered size 2 storm and wind slab avalanches were also observed on northwest, north, northeast, and east facing slopes. The avalanches were typically 30-40 cm thick. Natural avalanche activity was likely more extensive over the weekend given the intensity of the storms, but poor visibility would have limited observations.

A similar pattern of naturally and human triggered slab avalanches can be expected this week, especially during the peak intensity of the storms on Monday night and Tuesday night.

New storm and wind slabs will form throughout the week as a series of frontal systems bring more snow and wind to the region. This new snow will add to 25-50 cm of heavily wind-affected snow from the weekend (although sheltered terrain may still hold low density powder). There are a couple of crusts beneath recent storm snow including a rain crust below 1200 m and sun crusts on south and west facing slopes.

Recent observations suggest the lower snowpack is strong and well-bonded in many parts of the region. However, given the large extent of the region it remains important to understand snowpack conditions in your local riding area. The Pine Pass area has a layer of surface hoar roughly 100 cm below the surface that was a problem around treeline elevations in mid-February, but appears have gained strength since then. The eastern slopes of the Rockies have many shallow rocky slopes that could harbour weak basal facets.

Cornices have grown large and should be given wide berth, especially if you're travelling on ridge lines.

• Dial back your terrain choices if you are seeing more than 20 cm of new snow.
• Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
• Make conservative terrain choices and avoid overhead hazard.
• Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.