Avalanche Forecast

Issued: Feb 19th, 2018 4:52PM

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

mgrist, Avalanche Canada

Purcells.

Fresh wind slabs and cornices have formed at higher elevations. Riding preserved powder in sheltered trees is a good option.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Clear and cold for the foreseeable future, with overnight lows near -24 Celsius in some locations. TUESDAY: Cloudy with sunny periods and isolated flurries. Tree line temperature around -14 Celsius. Light winds northerly 5-15 Km/hr.WEDNESDAY: Cloudy with sunny periods and isolated flurries. 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 westerly.

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. 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 remain reactive and could be slow to gain strength due to a mix of underlying weak surfaces. Watch for new wind slab development and reverse loading due to northwest through northeast winds.

Avoid travelling in areas that have been reverse loaded by winds.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 20th, 2018 2:00PM