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Avalanche Forecast

Archived

Mar 16th, 2019–Mar 17th, 2019

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

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.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.