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Avalanche Forecast

Archived

Jan 27th, 2019–Jan 28th, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

The snowpack in the Purcells this season is exceptional, and not in a good way. We've summarized our thoughts on this precarious snowpack in the latest forecasters blog here. Take it easy out there, this is not the time for the big lines.

Confidence

High -

Weather Forecast

High pressure, cold temperatures and clear skies should allow for great visibility Monday and Tuesday. Cloud cover starts to build back in Wednesday, but the models are not showing any significant precipitation until Friday.SUNDAY NIGHT: Freezing level at valley bottom, light to moderate north/northwest wind, trace of precipitation possible.MONDAY: Clear skies at dawn, with a few clouds building in the afternoon, freezing level at valley bottom, light northerly wind, no precipitation expected.TUESDAY: Clear skies, freezing level at valley bottom, light west/northwest wind, no precipitation expected.WEDNESDAY: Scattered cloud cover, freezing level at valley bottom, light northwest wind, trace of precipitation possible.

Avalanche Summary

On Friday and Saturday wind slab avalanches up to size 2 were reported from east and northeast aspects between 1900 and 2400 m. One skier-triggered avalanche was reported on Wednesday in storm snow at approximately 2000 m that released 40 cm below the surface. On Thursday, explosive control work released another slide on the deep persistent layer at the base of the snowpack. There is a great MIN report from last Saturday that shows a natural avalanche (size 3.5) in International Basin, also on the deep persistent layer. Check out the MIN here.

Snowpack Summary

Saturday delivered warmth and strong to extreme wind out of the south, southwest and northwest. This left a crust on steep south facing aspects and likely redistributed quite a bit of snow into fresh and potentially deep wind slabs in lee alpine features. The warmth also allowed 10 to 50 cm of snow to continue to consolidate above the mid-January persistent weak layer (PWL). This PWL is made up of large surface hoar that is most prevalent at and below treeline. On steep solar aspects this interface presents as a crust, there may be locations where the surface hoar actually sits on the crust.The snowpack is also harboring a nasty weak layer near the ground that is made up of weak faceted grains above a crust. This interface continues to produce sporadic avalanches that are very large and destructive. Avalanches triggered on this weak layer take the entire seasons snowpack with it and have resulted in numerous close calls and serious incidents. This layer is most likely to be triggered from zones where the snowpack is thin and weak. Rock outcroppings and ridge crests around large open slopes and bowls in the alpine are particularly suspect

Problems

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.