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Avalanche Forecast

Archived

Jan 12th, 2019–Jan 13th, 2019

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

South Rockies.

A big rise in freezing levels may mean that the deep persistent slab wakes up. A lot of uncertainty exists as to what this layer will do as temperatures climb. High levels of uncertainty are best managed by choosing conservative terrain.

Confidence

Low - Freezing levels are uncertain

Weather Forecast

A classic temperature inversion sets up Saturday night which will likely stick with us until Tuesday.  No significant precipitation is expected until possibly Friday.SATURDAY NIGHT: Temperature inversion with cold (below freezing) air in the valleys and above freezing temperatures between 1500 and 3200 m, light to moderate south/southwest wind, no precipitation expected.SUNDAY: Clear skies, temperature inversion with cold (below freezing) air in the valleys and above freezing temperatures between 1600 and 3000 m, light northwest wind at most elevations with moderate northwest wind at ridgetop, no precipitation expected.MONDAY: Clear skies and warm with the freezing level at 3000 m, light variable wind, no  precipitation expected.TUESDAY: A few clouds, freezing level at valley bottom, light variable wind, no precipitation expected. 

Avalanche Summary

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

10-20 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 over the coming days could re-activate this layer, resulting in a possible avalanche cycle.

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.