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Avalanche Forecast

Archived

Dec 30th, 2017–Dec 31st, 2017

Alpine
Natural avalanches possible, human triggered probable.
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 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.

Conditions are primed for human triggered avalanches: There's a buried weak layer in the snowpack, with a critical amount of recent storm snow sitting on top. Conservative terrain choices are key for safe riding this weekend.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Dry with cool temperatures for the foreseeable future. SUNDAY: Mostly sunny. Ridge wind light southwest. Temperature -14. Freezing level surface.MONDAY: Mix of sun and cloud. Ridge wind light southwest. Temperature -12. Freezing level surface.TUESDAY: Mix of sun and cloud. Ridge wind light west. Temperature -12. Freezing level surface.

Avalanche Summary

On Saturday several natural and human triggered storm slab avalanches to Size 2 were reported on a wide variety of aspects and elevations. Furthermore, several persistent slab avalanches to Size 1.5 were reported (with some remote-triggered by skiers). Earlier in the week, a larger persistent slab (Size 2) was triggered low on a slope that propagated up and across the slope on a 50 cm deep crust. This highlights the potential for persistent slab avalanches to have wide propagations.

Snowpack Summary

Up to 45 cm of snow has fallen over the past 2 days, with generally light winds. That said, some areas of the region (Crowsnest Pass) saw strong east winds while others (Elk valley) had lower snowfall amounts. In wind exposed areas this new snow overlies variable wind slabs up to 80 cm thick in some areas. In sheltered areas, 30-60 cm of unconsolidated old storm snow has been covered.The main question in the snowpack surrounds the mid-December layer sitting beneath the recent snow. This layer includes crusts on solar aspects and feathery surface hoar in sheltered terrain at and below treeline, and has produced whumpfing as well as moderate, sudden results in recent snowpack tests. The lower snowpack is composed of mostly soft sugary snow and a few early season crusts that have not produced significant test results recently.For an update on recent conditions check out the Mountain Information Network (MIN) report here. And please post your own reports!

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.

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.