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Avalanche Forecast

Archived

Mar 6th, 2021–Mar 7th, 2021

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

Regions

Sea To Sky.

New snow and wind will elevate the avalanche danger. Triggering avalanches at upper elevations is likely, especially in wind-drifted areas. Continue to make conservative terrain choices and steer clear of cornices while the snow settles and stabilizes. 

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

A parade of storms continues through the weekend

Saturday night: Overcast, 5-10 cm of snow, light south wind increasing to moderate, freezing level dropping to 700 m. 

Sunday: Mostly cloudy, 10-20 cm of snow, moderate southwest wind, freezing level near 1000 m. 

Monday: Partly cloudy, isolated flurries with trace accumulations, light east wind, freezing level near 1200 m.

Tuesday: Mainly sunny, light variable wind, freezing level near 1400 m.

Avalanche Summary

Explosive mitigation on Saturday produced numerous large cornice and storm slab avalanches, with 50-100 cm crown depths. Explosives also released a very large (size 3) wind slab avalanche on a northeast aspect above 2000 m. 

Reports indicate that a natural avalanche cycle occurred during the storm on Friday, with small to large (size 1-2.5) avalanches releasing in the storm snow across aspects and elevations. Check out this MIN report from Hanging Lake.

Snowpack Summary

Another 15-25 cm of snow is forecast to accumulate by midday on Sunday above 1000 m. This will add to the 50-80 cm of snow that blanketed slopes above 1600 m on Friday. The recent snow has been accompanied by strong south winds, forming touchier slabs on leeward slopes. Pay attention to how wind has redistributed snow and investigate the bond of the new and old snow interfaces as you travel in the backcountry on Sunday. Massive cornices exist on ridgelines, which can act as triggers on slopes below. A cooling trend over the weekend is expected to settle and strengthen lower elevation slopes that became saturated with rain. 

In isolated areas with a shallower snowpack in the region, a layer of facets, spotty surface hoar, and/or crusts buried in mid-February may still be preserved. There have been no avalanches reported on this layer; however, large triggers, such as an avalanche in motion, cornice fall, or intense loading from snow and wind have the potential to this deeper layer in areas where it may still exist.

The mid and lower snowpack is well settled and strong in most areas.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Cornice failure may trigger large avalanches.

Problems

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.