Archived

Avalanche Forecast

Dec 28th, 2018–Dec 29th, 2018

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Lizard-Flathead.

Rising freezing levels and increased wind will accompany snowfall. If more than 20 cm snowfall accumulates, the avalanche hazard will rise to CONSIDERABLE.

Confidence

Low - Freezing levels are uncertain

Weather Forecast

FRIDAY NIGHT: Cloudy with isolated flurries, up to 10 cm accumulation. Light to moderate southwest wind. Alpine low of -12C.SATURDAY: Flurries, 5-15 cm accumulation. Moderate southwest wind gusting strong to extreme. Alpine high -4, freezing level rising above 1400 m.SUNDAY: Mix of sun and cloud with scattered flurries, trace to 5 cm accumulation. Light northwest wind gusting moderate to strong. Freezing level dropping to valley bottom, alpine high -3C.MONDAY: Mix of sun and cloud. Light northwest wind with occasional moderate gusts. Alpine low -15C.

Avalanche Summary

Small (size 1) wind slabs have been reactive to skier traffic in the region.A great MIN report from Corbin on Thursday identifies a few slabs initiating in thin, rocky areas on a south aspect. Check out the report here.Over the last weekend, the persistent weak layer was active, explosives triggered avalanches to size 2.5 and a cornice triggered a size 2 avalanche. Skier traffic was also able to trigger wind slab avalanches to size 2. Though avalanche activity on this layer has slowed, avalanches failing on this layer have the potential to be large and destructive.

Snowpack Summary

Around 20 cm fresh snowfall accumulated through the week has been redistributed around lee areas at treeline and alpine elevations. In total, 60-110 cm of snowfall through December has formed a slab that sits on a persistent weak layer that formed in early December. This layer mostly consists of facets (sugary snow) with some isolated areas also containing small surface hoar (feathery crystals). This overlies several other weak layers observed in the lower snowpack such as crusts and facets that formed in late October/early November. With this weak basal snowpack, it is likely that an avalanche triggered on the persistent slab would step down to these lower layers, resulting in a full depth avalanche.

Avalanche Problems

Persistent Slabs

60-110 cm of snow sits on a weak layer consisting primarily of facets (sugary snow). Winds have redistributed recent snow and slabs may be more reactive in wind-loaded areas.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Be wary of slopes that did not previously avalanche.Avoid convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3

Wind Slabs

Winds are redistributing snow and slabs are forming in wind-loaded terrain.

Be cautious as you transition into wind affected terrain.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1 - 2