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Avalanche Forecast

Feb 17th, 2018–Feb 18th, 2018
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Purcells.

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

Confidence

Moderate - Due to the number of field observations

Weather Forecast

The very south of the region may see lingering flurries on Sunday; otherwise, we're looking at clear and cold from Sunday onwards, with overnight lows near -25 Celsius in some locations. Sunday: Mostly cloudy but cold. Isolated flurries in the south. Tree line temperatures around -15 Celsius. Winds light to moderate northeasterly.Monday: Sunny with cloudy periods. Tree line temperature around -14 Celsius. Winds light northerly.Tuesday: Cloudy with sunny periods. Tree line temperature around -13 Celsius. Light winds becoming moderate northerly. 

Avalanche Summary

On Friday, 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. On Wednesday, a few small avalanches, including one involving a skier, were reported in recent storm snow with crowns approximately 30 cm deep.A week ago, explosive control work continued to produce large, deep avalanches up to size 3 on north to southeast aspects above 2200m. On the same day, a skier is believed to have remotely (from a distance) triggered a size 1.5 avalanche on a northwest aspect at 2800m that failed on the early January layer.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 10-20cm with more in the very south of the region: Dial back your terrain use if you are seeing more than 25 cm of new snow in your location. 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.

Avalanche Problems

Wind Slabs

Wind slabs may be especially reactive and slow to gain strength due to a mix of underlying weak surfaces. Watch for new wind slab development and reverse loading due to strong 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