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Avalanche Forecast

Mar 20th, 2016–Mar 21st, 2016
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
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: Purcells.

Watch for fresh storm slab formation at upper elevations and continue to seek out conservative terrain in an effort to avoid tangling with the deeply buried persistent weak layers.

Confidence

Moderate

Weather Forecast

A weak upper low moves into the region Monday displacing the ridge that was in place over the weekend. With the ridge collapsed, the door is open to a series of fast moving storms interspersed by the odd ridge. SUNDAY NIGHT: Freezing level around 2000 m, 1 to 5 cm of snow above 2000 m, rain below, moderate SW wind. MONDAY: Freezing level around 1700 m, 1 to 3 cm of snow at and above treeline, light to moderate southwest wind. TUESDAY: Freezing level starting near valley bottom rising to about 1700 m, light northwest winds, no significant precipitation. WEDNESDAY: Freezing level starting near valley bottom rising to about 1600 m, trace of snow possible, light southwest wind.

Avalanche Summary

On Saturday several natural and explosive initiated cornice failures to size 2.5 were reported. In the north of the region on friday control work produced several size 2 to 3 persistent slab avalanches on high elevation north through east facing features. These avalanches were failing on the mid and early February persistent weak layers.

Snowpack Summary

At ridgetop, cornices are huge and remain weak. Old wind slabs still linger on lee features at treeline and in the alpine which may become more reactive with solar radiation. 40-90cm below the surface you'll find a persistent weak layer comprised of surface hoar, facets and/or a thick crust. This layer seems variably reactive. In other words, it's still reactive to human triggers in some places while in other spots it's really tough to trigger, and there's not much of a reliable pattern telling us what exact aspects are most suspect. I'd continue to be suspicious of steep, unsupported features at treeline and in the alpine as this layer has the potential to produce large avalanches. Deeper weak layers from mid-February and early January are now down 50-90cm and 70-120cm respectively. Triggering an avalanche on either of these layers has become unlikely but still has the potential to produce very large avalanches in isolated locations with a heavy trigger or significant warming.

Avalanche Problems

Cornices

Large unstable cornices overhang countless ridge lines and many of these cornices are teetering on the brink of failure.  The weight of an approaching rider, a bit of wind or a period of sunshine could easily induce natural collapse.
Do not travel any where near cornices Monday! These behemoth chunks of dense snow could collapse at any moment, and you don't want to be underneath one when it fails.>

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 3 - 5

Persistent Slabs

There are a few different persistent weak layers in the snowpack that are capable of producing large destructive avalanches.  While these interfaces are likely getting harder to trigger, they remain problematic.
Be aware of the potential for large, deep avalanches due to the presence of a few different persistent weak layers.>Continue to seek out well supported conservative terrain as you plan your day in the mountains.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 3 - 6

Storm Slabs

Sunday night's storm should produce 1 to 5 cm of new snow accompanied by moderate to strong southwest winds.  Watch for fresh slab formation in wind exposed features at and above treeline.
Be alert to conditions that change with elevation.>Avoid freshly wind loaded features.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2