Avalanche Forecast

Archived

Dec 3rd, 2017–Dec 4th, 2017

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

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 possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

Warmer temperatures expected in the alpine 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: Mostly cloudy with new snow 5-20 cm. Alpine temperatures near 0 degrees and freezing levels rising to 1400 m. Ridgetop winds strong from the west. Tuesday: Mix of sun and cloud. Alpine temperatures high of plus 3 and freezing levels 1600 m. Ridgetop winds moderate from the west.Wednesday: Sunny with valley cloud and alpine temperatures reaching a high of plus 9. Freezing levels 2000 m with a very strong alpine temperature inversion. Ridgetop winds moderate from the southwest.Expect strong inversions in the alpine up to 3000 m. For detailed information visit the Mountain Weather Forecast.

Avalanche Summary

On Sunday, dry loose avalanches were reported up to size 1. On Saturday, reports indicated several natural wind slab avalanches up to size 2 on northerly aspects in the alpine and dry loose avalanches from steeper terrain up to size 1 treeline and above. I remain suspect of the new snow and the bond to the buried crusts, especially the basal crust. I would be diligent and use a conservative approach to route selection while traveling through low consequence terrain, especially headed into the warmer weather forecast. Check out the Mountain Information Network for recently posted observations around the Shames area. Give info, get info.

Snowpack Summary

Recent accumulated storm snow amounts are from 100-130 cm and seem to be settling quickly with average snowpack depths 100-150 cm at treeline elevations. Deeper deposits of wind slab may be found on leeward slopes. This storm snow now sits above a 5-10 cm thick crust that was buried a week ago. Digging down 90-160 cm exists a crust/facet combo buried at the end of October. Recent snowpack test results are showing hard compression tests with sudden collapse results. I would keep this on my radar through the weekend to see how the snowpack adjusts to the new load.

Problems

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.

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.