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Avalanche Forecast

Archived

Dec 23rd, 2019–Dec 24th, 2019

Alpine
Natural avalanches possible, human triggered probable.
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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You can trigger large and dangerous avalanches on old weak layers of snow. Use caution near slopes 35 degrees and steeper and avoid lingering below steep terrain. The western half of the zone, near the Cascade Crest, holds the most dangerous conditions after a major winter storm hit the area last week.

Discussion

Observers at Holden Village and in the Icicle Creek drainage reported a cycle of large, natural avalanches on Friday and Saturday. 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. The avalanche activity and snowfall were more significant in the western half of the zone, closer to the Cascade Crest. Snow totals ranged widely across the zone. Mission Ridge received less than 5” of snow while areas near to the Cascade Crest received up to 7” of water equivalent and now hold over 3 feet of settled storm snow on the ground. Rain fell at many locations Saturday and Sunday up to 5,000ft.

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.