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Avalanche Forecast

Archived

Dec 18th, 2019–Dec 19th, 2019

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

Regions

South Rockies.

Triggering an avalanche is most likely in wind affected terrain and steep, rocky slopes.

Confidence

No Rating - Uncertainty is due to the limited number of field observations.

Weather Forecast

Wednesday Night: Mostly cloudy. Alpine temperature -10 C. Southwest wind 25-35 km/hr.

Thursday: Flurries, trace to 5 cm. Alpine temperature -6 C. Southwest wind 20-35 km/hr.

Friday: Snow, heavy at times 20-30 cm. Alpine temperature -3 C. Southwest wind 20-40 gusting to 80 km/hr. Freezing level rising to 1900 m.

Saturday: Continued flurries, 5-15 cm. Alpine temperature -2 C. Southwest wind 30 gusting to 75 km/hr. Freezing level 1600 m.

Avalanche Summary

Explosives triggered 2 small (size 1) wind slabs on Wednesday. A few small (size 1) natural avalanches were noted around the Castle area on Tuesday and skiers reported fresh wind slabs cracking underfoot.

Snowpack Summary

Wind has scoured exposed terrain and formed wind slabs in the alpine, and around lee features and lower into start zones.

The bottom half of the snowpack consists of crusts from November and October and basal facets. These persistent weak layers produced large avalanches over a week ago but have since gained strength. Overall, a shallow and variable snowpack is found around the region. Snowpack depths range between 50-100 cm around treeline and taper rapidly below.

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.

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.