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Avalanche Forecast

Dec 30th, 2017–Dec 31st, 2017
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: South Columbia.

The new year will bring a more stable weather pattern along with gradually warming temperatures. Consider the potential to trigger persistent slabs as the recent storm snow starts to finally settle and consolidate more rapidly.

Confidence

Moderate - Freezing levels are uncertain on Tuesday

Weather Forecast

SUNDAY: Mix of sun and cloud / Light to moderate west wind / Alpine temperature -10 MONDAY: Mix of sun and cloud / Light to moderate northwest wind / Alpine temperature -5 TUESDAY: Mix of sun and cloud / Moderate northwest wind / Alpine temperature 2, possible temperature inversion

Avalanche Summary

Recent reports show numerous natural and human triggered loose dry avalanches in steep terrain to size 1.5 and also a few natural storm slab avalanches to size 2 in the alpine. There have been a few reports of persistent slab avalanches both naturally and remotely triggered to size 1.5 and 2 on north aspects between 2000 and 2200m. Consider the potential to trigger persistent slabs on top of the mid December persistent weak layer as the temperature rises and the storm snow begins to settle and consolidate more rapidly in the coming days.

Snowpack Summary

35-65cm of low density new snow from the past 3 days has buried a recently formed layer of weak feathery surface hoar and/or sugary facets. A layer buried mid-December that consists of surface hoar, sun crust and/or sugary facets is now down approximately 60-100cm.The bond at this old snow interface is of critical importance in areas where the overlying snow has consolidated into a slab. The most concerning areas are those that saw pronounced surface hoar development before the storm, such as sheltered areas at and below treeline, sheltered northerly aspects in the alpine, or anywhere the surface hoar formed on top of a sun crust. Recent snowpack tests show wide ranging reactivity on this weak layer but suggest that it may be most reactive on northerly aspects. A rain crust that formed in late November is now buried 100-140cm deep. Recent evidence from the North Columbia region suggests it may be reactive in steep, variably loaded terrain features in the alpine.

Avalanche Problems

Storm Slabs

35 to 60cm of low density new snow has accumulated in the region the past 3 days. Where accumulations are higher expect the new snow to sluff and gather mass in steep terrain. West and northwest winds have created windslabs in alpine lees.
Be cautious as you transition into wind affected terrain.Sluffs may trigger deeper instabilities.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 2

Persistent Slabs

A weak layer of surface hoar buried 60-100 cm deep has potential to produce large avalanches where the overlying snow has settled into a cohesive slab.
Buried surface hoar is more likely to be preserved in sheltered openings at and below tree line.Watch for signs of slab formation, such as wind effect, whumpfing, or shooting cracks.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 3