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Avalanche Forecast

Mar 15th, 2012–Mar 16th, 2012
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
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
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

Regions: South Rockies.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

A deep trough off the coast continues to move an unstable air mass through the forecast period. Friday: Mainly cloudy skies, possible sunny breaks in the afternoon. Snow amounts 5-10 cm. Ridgetop winds light from the SW. Alpine temperatures near -8. Freezing levels 1700 m. Saturday: Cloudy. Light-moderate snow amounts later in the day, overnight. Ridgetop winds moderate from the SW. Freezing levels 1600 m. Sunday: Mainly dry conditions. Broken skies and sunny periods. Solar radiation will be intense. Ridgetop winds light from the West. Freezing levels 1100m.

Avalanche Summary

Only audible avalanche activity reported from upper elevations in the Crowsnest North. In the Lizard Range loose wet avalanche activity occurred on all aspects below 1600 m. This may have also occurred in areas of the S. Rockies. On Tuesday explosive controlled avalanches up to size 1.5 were reported. On Monday, skiers triggered size 1-1.5 soft slabs in steep terrain. A widespread natural avalanche cycle occurred up to size 3 in response to very warm temperatures and loading of start zones by strong winds last Friday and Saturday. Video footage here: https://bit.ly/yR4E8r . Last Friday, a snowmobiler was killed in a size 3 slab on a south-west aspect at treeline in the Corbin Creek area and a skier was injured in an avalanche in steep terrain in the Flathead Range. Over the last week, there were several reports from in or near the region of near misses, including a snowmobiler who triggered an avalanche and was buried for around 30 minutes, remote-triggered avalanches, and slab avalanches running into unusually low-angled terrain. With forecast snow, wind and warming; I expect the region will see another natural avalanche cycle. Conditions continue to remain tricky to predict, and manage. Large avalanches are still possible due to buried weak layers. Expect avalanche danger to elevate with unsettled weather conditions, and possible solar radiation, which will deteriorate the upper snowpack.

Snowpack Summary

Earlier in the week the region has received 30-40 cm of storm snow. An additional 15-25 cm fell overnight Wednesday. Touchy storm slabs exist at all elevations. Strong SW winds have created stiff wind slabs behind ridges and terrain breaks. The mid February surface hoar layer in the upper snowpack is most prevalent in the west and south of the region, particularly in the Flathead. Recent snowpack tests, as well as rider-triggered avalanches, on this weak layer indicate that it still has the potential to be triggered in many areas, resulting in a large destructive avalanche. Remote-triggering, triggering from below and triggering on low-angled terrain are also concerns. Basal facets may still exist, particularly in shallower snowpack areas with steep, rocky start zones. Cornices have grown large and threaten slopes below. Conditions are variable across the region.

Avalanche Problems

Wind Slabs

Wind slabs may be found on lee slopes, behind ridges and terrain breaks.

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

Elevations: Alpine, Treeline.

Likelihood: Likely - Very Likely

Expected Size: 1 - 6

Storm Slabs

Storm slabs will continue to build through the forecast period. Loose sluffs are also a possibility in steep terrain. Storm slabs and sluffs could step down to a persistent weak layer, creating destructive avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 6

Persistent Slabs

A persistent weak layer around 1m deep has the potential to produce large and dangerous avalanches. It could be triggered by the weight of a person, remotely or in surprisingly mellow terrain. It is tricky to manage this problem, so be conservative.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 3 - 7