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Avalanche Forecast

Archived

Mar 17th, 2021–Mar 18th, 2021

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

Regions

Northwest Inland.

Light new snow and elevated winds should keep wind slab problems fresh and reactive to triggering in exposed areas. Monitor new snow accumulation and wind transport and be ready to step back if snowfall exceeds the forecast or you observe slab formation at lower elevations.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Wednesday night: Cloudy. Moderate to strong southwest winds.

Thursday: Cloudy with isolated flurries and a trace to 5 cm of new snow, continuing overnight. Moderate to strong southwest winds. Alpine high temperatures around -6.

Friday: Cloudy with continuing scattered flurries and a trace to 5 cm of new snow. Moderate to strong southwest winds. Alpine high temperatures around -9.

Saturday: Cloudy with isolated flurries and a trace of new snow, increasing a bit overnight. Alpine high temperatures around -9.

Avalanche Summary

No new natural avalanches were reported on Tuesday with limited field observations. A few size 1 skier triggered wind slab avalanches in the alpine were reported on Monday.

A natural avalanche cycle with storm slab avalanches up to size 2.5 (large) were reported in the southwest of the region throughout the weekend. 

Snowpack Summary

About 5 cm per 12 hour period is expected to accumulate over the next couple of days, adding to 20-30 cm of new snow and snow from over the weekend. Storm totals in the southwest of the region are closer to 50-100 cm. Light forecast snow amounts and elevated winds are expected to continue forming fresh wind slabs on lee features below alpine ridgetops. At lower elevations, recent precipitation fell as rain. 

Collectively, our new and recent snow overlies a variety of surfaces, including hard wind affected snow at alpine elevations, weak surface hoar crystals on northerly aspects and in sheltered terrain features around treeline, or a melt-freeze crust on southerly aspects and below treeline.

The mid and lower snowpack is reported as well settled and strong in most areas. However, weak facets exist at the base of the snowpack in the more shallow snowpack zones within much of the region and always have the potential of being triggered on steep, rocky slopes with a shallow or thin to thick snowpack; especially with large loads such as a cornice fall.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

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.