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Avalanche Forecast

Mar 19th, 2016–Mar 20th, 2016
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
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.

Freezing levels spike on Sunday which will increase the likelihood of large natural and human triggered avalanches. Avoid slopes with overhead exposure where falling cornices could trigger large avalanches.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

There's a fair bit of model disagreement but freezing levels are forecasted to spike to as high as 2600m on Sunday with cloudy skies and possible flurries overnight. Monday looks cloudy with lowering freezing levels. Tuesday should be clear and cool with freezing levels dropping sharply. Light to moderate southerly winds until Monday evening when they calm down.

Avalanche Summary

On Friday, explosive control work inside a permanent closure at Kicking Horse Mountain Resort produced several size 2-3 slab avalanches which failed on both the mid and early February weak layers. This tells us that these weak layers are still alive and well even though they may be difficult to trigger in most areas. Small loose wet avalanches and failing cornices triggering slab avalanches on the late February layer would be on the forefront of my mind as I travel through the mountains this weekend.

Snowpack Summary

At ridgetop, cornices are huge and could become increasingly touchy with rising freezing levels and solar radiation. 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

Rising freezing levels and solar radiation will promote large cornice failures which could, in turn, trigger a large avalanche on the slope below.
Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>Extra caution needed around cornices with current conditions.>

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 3 - 6

Persistent Slabs

Small loose wet avalanches and failing cornices triggering slab avalanches on the late February layer would be on the forefront of my mind as I travel through the mountains this weekend.
Use conservative route selection, stick to moderate angled terrain with low consequence.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 3 - 5

Loose Wet

As the sun comes out, surface avalanche conditions will include a mix of wind slabs in high elevation lee terrain, and pushy loose wet activity on steep, sun-exposed slopes. Loose wet avalanches may also trigger deep and destructive slab avalanches.
Watch for clues, like sluffing off of cliffs, that the snowpack is warming up. >Sluffs may trigger deeper instabilities.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

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

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 3