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Archived

Avalanche Forecast

Jan 19th, 2017–Jan 20th, 2017
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: Northwest Inland.

Uncertainty about deep persistent slabs warrants a conservative approach to terrain after the storm.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

FRIDAY: Cloudy, light southwest winds, freezing level dropping with alpine temperatures around -5 C.SATURDAY: Cloudy with isolated flurries, moderate southeast winds, alpine temperatures around -8 C.SUNDAY: Cloudy with sunny periods, light southeast winds, alpine temperatures around -8 C.

Avalanche Summary

On Wednesday, several loose wet avalanches were reported from steep rocky terrain at lower elevations where rain fell on snow. Storm slabs sitting on a weak layer of surface hoar and/or a crust are likely easy to trigger at higher elevations. Full depth avalanches continue to be a concern due to the weak faceted snowpack below old hard wind slabs. This deep persistent weak layer may take prolonged warm weather with consistent snowfall to settle and bond.

Snowpack Summary

20-25 cm of new storm snow has been transported by southwest winds and now sits on a mix of old surfaces left behind after the recent cold and windy weather. Expect the new storm snow to bond poorly where it is sitting on a weak layer of buried surface hoar and/or a hard old wind polished surface. The freezing level recently reached 1000 m, and below this level the snowpack is likely moist and will eventually form a hard crust. Most areas continue to have a shallow and weak snowpack that is about 120-150 cm at treeline. In general, the snowpack above treeline has been heavily wind effected; this has resulted in hard wind slabs above weak faceted snow.

Avalanche Problems

Deep Persistent Slabs

Recent storm snow combined with warming and wind has loaded hard slabs above a weak faceted base. Uncertainty revolves around what type of load is now required to trigger these deep persistent slabs.
Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Stick to simple terrain and be aware of what is above you at all times.Avoid slopes with convexities or variable snowpack depths. Thin weak spots are likely trigger points

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 3

Storm Slabs

Recent snow, warming, and strong winds have created a widespread storm slab problem, particularly on wind-loaded features. Storm slab avalanches in motion may step down and trigger deep persistent slab avalanches.
The new snow will require several days to settle and stabilize.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2