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Archived

Avalanche Forecast

Mar 16th, 2019–Mar 17th, 2019
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
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
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
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.

Warming is coming! This significant change will weaken the snowpack. Forecasting the timing of changes over the next several days is difficult. However, it's easy to see it's time to reign in your terrain choices and stay clear of overhead hazards.

Confidence

Moderate -

Weather Forecast

Significant warming in the forecast and next week looks very warm with freezing level above the summits. Don't let overnight cooling at low elevations fool you; very little cooling is expected at higher elevation.SATURDAY NIGHT: Clearing, alpine low temperature O to -5C, light southwest wind.SUNDAY: Sunny, with freezing level approaching 2200m, no overnight re-freeze expected. Light variable wind.MONDAY: Sunny with freezing level around 2500m, no overnight re-freeze expected. Light variable wind.TUESDAY: Sunny with freezing level around 2500m and alpine tempertures around +5C. Light variable wind.

Avalanche Summary

Small dry loose, wet loose, and small windslabs up to size 2 continue to be observed in the region.On Thursday, a group of riders remotely triggered a size 1.5 persistent slab from 100 metres away. See the MIN report for more details. Although this occured in the neighbouring Lizard & Flathead region, I view it as an important piece of data when considering the effect of forecast strong sunshine and warming.

Snowpack Summary

Moderate to strong southwest winds have affected the low density storm snow at and above treeline, building winds slabs near ridgetop and behind lee features. These fresh slabs overly old slab slabs in alpine terrain. The sun has transformed the recent 15-20 cm of storm snow which became moist on southerly aspects at lower elevations. The middle snowpack consists of weaker faceted snow with few if any distinct layers. In isolated wind protected locations a thin surface hoar layer from mid-January is 50-80 cm deep. The surface hoar is most prominent in the Elk Valley between 1600 m and 1900 m. Regardless of whether they are facets or surface hoar crystals, when the weather warms they may produce avalanches.

Avalanche Problems

Storm Slabs

Sunshine and warming temperatures will peel away layers or recent snow on sunny slopes as loose wet slides, weaken cornices, and possibly re-energize wind slabs. The key unknown is how warming and weakening upper snowpack will affect deeper layers.
Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.Parking, eating lunch, and regrouping in runout zones is bad practice.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2

Persistent Slabs

A surface hoar layer formed in late January may be more reactive than expected, especially at lower elevations during periods of intense warming. See this MIN report for a recent remotely triggered avalanche attributed to sunshine and warming.
Be cautious in shallow snowpack areas where triggering is more likely.Remote triggering is a concern, watch out for adjacent slopes.Warming could wake up buried weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Unlikely - Possible

Expected Size: 1 - 2.5