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Avalanche Forecast

Feb 16th, 2018–Feb 17th, 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
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

Regions: Purcells.

Danger ratings are based on 5-10 cm of new snow on Saturday. If you see more than 25cm of new snow (possible in the south of the region) consider the danger to be HIGH . Buried weak layers increase the potential size of avalanches.

Confidence

Moderate - Track of incoming weather systems is uncertain on Saturday

Weather Forecast

The south of this region will see significantly more snow from the storm on Saturday (15-20cm possible). Clearing and becoming cold on Sunday as frigid arctic air moves inSATURDAY: Snow (15-20 cm possible in the far south with 5-10cm more likely near Golden). Tree line temperature around -12C. Winds southwesterly 30km/h.SUNDAY: Clearing, but lingering flurries possible. Tree line temperatures around -20C. Winds light northeasterly.MONDAY: Sunny but cold. Alpine temperatures near -18 Celsius. Winds light 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. I suspect moderate south west through north west winds shifted these accumulations into deeper, reactive slabs in wind-exposed terrain. These accumulations overlie 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 treeline.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

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

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 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: 2 - 4