Avalanche Forecast

Archived

Dec 3rd, 2017–Dec 4th, 2017

Alpine

Natural avalanches unlikely, human triggered possible.

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.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely.

Regions

Northwest Inland.

Warmer temperatures expected in the alpine by Tuesday with a strong temperature inversion by Wednesday. Avalanche hazard will likely increase during this time of change.

Confidence

Low - Due to the number and quality of field observations

Weather Forecast

Monday: Mix of sun and cloud with new snow 5-10 cm. Alpine temperatures near -8 and Freezing levels rising to 700 m. Ridgetop winds strong from the west. Tuesday: Mix of sun and cloud. Alpine temperatures near -2 and freezing levels 1000 m. Ridgetop winds moderate from the west.Wednesday: Sunny with valley cloud and alpine temperatures reaching a high of plus 7. Freezing levels 400 m with a very strong alpine temperature inversion. Ridgetop winds light from the southwest.Expect strong inversions in the alpine up to 3000 m. For detailed information visit the Mountain Weather Forecast.

Avalanche Summary

No recent avalanche activity has been reported. Stiff wind slabs may exist at treeline and in the alpine on leeward slopes and cross-loaded features. If triggered, these could step down and trigger deeper weak layers, initiating large avalanches. The last significant avalanche observation was submitted on November 28th from Skilokis Cr. A size 2.5 persistent slab was triggered from 150 m distance away. This problem will likely linger. Check out the Mountain Information Network for more details. Give info, get info.

Snowpack Summary

Alpine snow surfaces are likely wind affected with average snowpack depths 80 cm -140 cm at treeline elevations, and up to 160 cm in the alpine. Approximately 30-50 cm of recent snow now overlies two crusts that were buried near the end of November. Recent snowpack tests have shown sudden planar results at this crust interface. These crusts are widespread and extend well into the alpine. Below these crusts exists a well settled mid pack overlying the late October crust near the base of the snowpack. This late October "crust/facet combo" is widespread and has been reactive to rider triggers.

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.