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Avalanche Forecast

Archived

Dec 25th, 2019–Dec 26th, 2019

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.

Regions

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Though becoming less likely, it is still possible to trigger a deep and wide avalanche where a slab rests over weak, older snow near the ground. Higher elevations, and slopes with a shallow snowpack that face the north half of the compass are the most concerning. Use extra caution before entering slopes steeper than 35 degrees in these areas. 

Discussion

It has been a number of days now since the big storm event last weekend. Observers at Holden Village and in the Icicle Creek drainage reported a cycle of large, natural avalanches on the 20th and 21st. These avalanches were easily big enough kill a person (up to size D2.5). Some broke widely across the terrain, ran on weak old facets, and may have been triggered remotely. On the 23rd, Mission Ridge Ski Patrol got results with explosive work below the Microwave Tower. The slab was observed to have failed on a layer of facets over a crust, which coincides with the same layer of concern we have closer to the crest. Yes, the likelihood of triggering slides on weak layers near the ground are slowly tapering off, but they may still be possible. Persistent slabs bring uncertainty, but we do know that they are more likely above 6,000ft, and on northerly facing slopes. Watch this video I put together from my field day in the Icicle drainage on the 23rd for more info.

A refrozen melt freeze crust can be found up to around 5,500ft throughout much of the zone, making travel difficult at these lower elevations. It is also very unlikely you'll trigger avalanches at these lower elevations because of refrozen conditions.

 

Snowpack Discussion

New Regional Synopsis coming soon. We update the Regional Synopsis every Thursday at 6 pm.

Problems

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.