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Avalanche Forecast

Archived

Feb 16th, 2017–Feb 17th, 2017

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

Regions

South Rockies.

New snow and rain has created touchy snowpack conditions. Give the snow time to settle before pushing into bigger terrain.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

THURSDAY NIGHT: Another 5 cm of new snow with greater accumulations to the south as a cold front passes through. Strong southwest winds and freezing level dropping to 1500 m.FRIDAY: Cloudy with sunny periods, moderate southwest winds, freezing level around 1500 m.SATURDAY: Cloudy with light flurries starting in the afternoon, light to moderate winds, freezing level around 1300 m.SUNDAY: Cloudy, moderate southwest winds, freezing level around 1500 m.

Avalanche Summary

Recent observations have been limited; however, a few size 2 solar-triggered persistent slab avalanches were observed in the Elkford area on Tuesday. They were thought to be about a day old and appeared to have failed on the December facets. Gradual cooling should help to limit natural avalanche activity at this interface. However, the December facet layer will be with us for a while and should not be trusted as we enter a low-probability/ high consequence pattern with this layer. Wind slabs will also remain reactive to human triggers at higher elevations.

Snowpack Summary

The region received 5-15 mm of precipitation on Thursday, which fell as rain in the valleys and as snow above 1800 m. Moderate to strong southwest winds are shifting these accumulations into reactive wind slabs in exposed high elevation terrain. Beneath the new snow, you'll find a mix of hard old wind slabs, melt-freeze crusts, and moist snow from the recent warm spell. Some weaknesses may still exist within the 90 cm of storm snow from last week; however, recent warming has likely helped to strengthen these layers. In deeper areas, the mid and lower snowpack appear to be well settled with only isolated concerns about the mid-December facet layer which comprises the bottom third of the snowpack. In shallow snowpack areas, this layer is weak, faceted, and has no structure. In these areas, snowpack test results and reports of whumpfing suggest large avalanches remain a concern at this interface. Watch this video from the South Rockies field team for some recent results on deeper facet layers.

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.

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.