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Archived

Avalanche Forecast

Jan 28th, 2018–Jan 29th, 2018
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
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

Regions: Lizard-Flathead.

Precipitation combined with a rising freezing level on Monday will create dangerous avalanche conditions. Several large, destructive avalanches have occurred in recent days. Simple terrain, free of overhead hazard is strongly recommended.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Monday

Weather Forecast

MONDAY: Periods of snow, accumulations 20-30cm overnight Sunday through Monday / Moderate to strong southwest wind / Alpine temperature -1 / Freezing level 1500-1700m TUESDAY: Flurries, accumulation 5-10cm / Light to moderate southwest wind / Alpine temperature -3 WEDNESDAY: Flurries / Light southwest wind / Alpine temperature -2

Avalanche Summary

On Sunday several size 1.5 to 2 explosives controlled storm snow avalanches were triggered in the alpine on northeast aspects. Several large and very large avalanches have occurred on weak layers buried deep in the snowpack in recent days (including natural activity up to Size 3), highlighting that dangerous avalanche conditions exist within the region. Explosive control work on Friday and Saturday produced numerous storm slab avalanches Size 2-2.5, as well as several large, destructive Size 3-4, slab avalanches that failed on the mid-December and late-November layers, with crowns from 150-250 cm deep.

Snowpack Summary

About 60-100cm of settled storm snow now covers a layer of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) and sun crust on solar aspects, that was buried mid-January. Beneath the mid-January interface lie a number of very concerning buried weak layers. A layer of surface hoar from early-January is buried 90-110 cm below the surface. A weak layer buried mid-December (predominantly surface hoar and/or a sun crust) is around 120-160 cm below the surface at treeline and below treeline elevations. A rain crust with sugary facets buried late-November is near the bottom of the snowpack and is now up to 200-250 cm below the surface. All of these layers remain active and have produced recent large, destructive avalanches.

Avalanche Problems

Storm Slabs

New snow and has formed touchy storm slabs, while winds are building cornice and loading lee slopes near ridge top. These slabs have shown the potential for wide propagations running long distances.
Avoid freshly wind loaded areas.If triggered, storm slabs may step down to deeper layers and result in large avalanches.Choose low-angle, well supported terrain without convexities.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1.5 - 2.5

Persistent Slabs

Several weak layers of concern are buried within the snowpack and produced several recent large and very large avalanches. Simple terrain with low angled, supported slopes is a good choice.
Watch for signs of instability such as whumpfing, or shooting cracks.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 4