Avalanche Forecast

Issued: Feb 20th, 2018 5:20PM

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

mgrist, Avalanche Canada

Purcells.

Wind slabs and cornices are the main concerns at higher elevations. Riding preserved powder in sheltered trees is a good option.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Cloudy Wednesday then clear and cold until light snow arrives on Friday. Overnight lows near -22 Celsius in some locations. WEDNESDAY: Cloudy with sunny breaks and isolated flurries possible. Tree line temperatures around -14 Celsius. Winds moderate westerly 20-30 Km/hr.THURSDAY: Sunny with cloudy periods. Tree line temperature around -12 Celsius. Winds light southeast 15 Km/hr.FRIDAY: Light snow (5-10 cm possible) . Tree line temperature around -11 Celsius. Moderate southwest winds 20-30 Km/hr.

Avalanche Summary

On Monday we received reports of a cornice triggered size 2.5 slab avalanche on a high north east alpine face near 2900m. We also received reports of natural wind slabs to size 2.5 (most crowns 20-40cm thick) on a wide range of aspects above 1900m elevation. On Sunday, several natural wind slab avalanches to size 2 were reported on primarily east aspects between 2200m and 2600m.On Sunday, skiers were able to intentionally trigger small (size 1) wind slab avalanches in immediate down wind (lee) features near ridge crests. See here for an update on conditions near Golden. Although deeper, persistent avalanche activity is becoming less frequent, these avalanches point to the continued reactivity and destructive potential of these layers.

Snowpack Summary

Recent storm snow totals are 15-30 cm with more in the very south of the region near Kimberley, where totals are closer to 50 cm. Moderate south west through north west winds shifted these accumulations into deeper, reactive slabs in wind-exposed terrain. The recent snow sits on a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects and surface hoar on sheltered slopes.Below the snow surface several persistent weak layers make up a troublesome snowpack which is not tolerating recent storm loads. In the top 1-2 m of the snowpack, two surface hoar/ crust layers buried in January can be found. Expect to find one or other of these on all aspects and elevations.Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below tree line.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.

Problems

Wind Slabs

Wind slabs have been slowly healing thanks to cold temperatures and winds abating. That said, if you can use terrain features to avoid classic wind loaded pockets, it's best to do so.

Be cautious as you transition into wind affected terrain.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be careful with with loaded pockets, especially near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2.5

Persistent Slabs

Several troublesome layers exist in the snowpack and may be reactive to large triggers such as a cornice or storm slab release. Human triggering may also be possible in shallow or thin, rocky areas.

Avoid the runout zones of avalanche paths. Very large avalanches have been running full path.Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1.5 - 3.5

Valid until: Feb 21st, 2018 2:00PM