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Avalanche Forecast

Archived

Jan 13th, 2019–Jan 14th, 2019

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

Regions

South Rockies.

Slab avalanches may be increasingly sensitive to human triggering in the alpine Monday as warm temperatures reach their apex. Minimize exposure to steep slopes receiving direct sunshine.

Confidence

Low - Due to the number of field observations

Weather Forecast

A classic temperature inversion will be with us through Monday evening. No significant precipitation is expected until possibly Friday.SUNDAY NIGHT: Clear skies, temperature inversion with cold (below freezing) air in the valleys and above freezing temperatures between 1800 and 3200 m, alpine temperatures between 0 and +5 are expected, light northwest wind, no significant precipitation expected.MONDAY: Clear skies, temperature inversion with cold (below freezing) air in the valleys and above freezing temperatures between 1500 and 3000 m, alpine temperatures between 0 and +5 are expected, light southwest wind at most elevations with moderate northwest wind at ridgetop, no significant precipitation expected.TUESDAY: Mostly clear skies, freezing level at valley bottom, light variable wind, no significant precipitation expected. WEDNESDAY: Scattered cloud cover, freezing level at valley bottom, moderate to strong west/southwest wind, no significant precipitation expected.

Avalanche Summary

On Saturday a size 2 natural deep persistent slab avalanche was observed on a south facing feature around 2100 m, more details here.  There is also a great MIN report from the neighboring Lizard Range where a group of sledders share about their near miss on a steep southwest facing feature at ridgecrest.On Friday we received a great Mountain Information Network observation of natural activity on solar aspects, more details here. A size 2-2.5 natural avalanche was also reported on a north aspect at 2200 m on Friday. This avalanche was likely triggered by a rock fall, and ran on the deep persistent layer at the base of the snowpack.A few size 1 natural and explosives triggered avalanches were reported in the region on Thursday.

Snowpack Summary

10 to 20 cm of recent storm snow has been redistributed by strong winds and has formed wind slabs at upper elevations. This new snow sits on previous hard wind slabs, a scoured and shallow snowpack on exposed ridges, and soft snow in sheltered areas. Large variability in snow depths still exists in the region, ranging from almost no snow to nearly 200 cm in some areas. For average snowpack areas, expect to find weak and sugary faceted snow around 50 to 100 cm deep, which extend to the ground. This weak bottom half of the snowpack has been the culprit for large avalanches in the region over the past few weeks. Warming temperatures and sunshine Monday have the potential to re-activate this layer.

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.

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.