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Archived

Avalanche Forecast

Feb 6th, 2018–Feb 7th, 2018
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
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: Northwest Coastal.

New snow, wind and rising freezing levels will increase hazard ratings for Wednesday. Choose conservative terrain and avoid exposure to overhead avalanche hazard. The potential for large avalanches to run long distances exists.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

TONIGHT: Snow. Accumulation 10-15 cm. Ridge wind moderate, southwest. Temperature near 0. Freezing level 1200 m.WEDNESDAY: Snow. Accumulation 20-30 cm. Ridge wind moderate, southwest. Temperature near 0. Freezing level 1400 m.THURSDAY: Mostly cloudy, light flurries. Accumulation 2-4 cm. Ridge wind light, north. Temperature -6. Freezing level 500 m.FRIDAY: Mostly sunny. Ridge wind light, northeast. Temperature -10. Freezing level valley bottom.

Avalanche Summary

Monday evidence of a natural avalanche cycle from size 2.5 - 3.5 was reported on north to south aspects between 1000-1700 m, west of Terrace, with several persistent slabs suspected to have failed on the mid or early January layers during the height of the weekend's storm.Sunday north of Meziadin Junction a natural size 4 and a natural size 3.5 were observed on a southwest and northeast aspect at 1800-2000 m and are suspected to have failed on the mid-January layer.On Saturday wind and storm slab avalanches failed naturally to size 2 on a variety of aspects in both alpine and treeline elevation bands. A natural size 3 persistent slab avalanche was observed on a steep north facing alpine feature with a crown up to 100 cm in depth, which suggests the mid-January interface was involved. A another very large avalanche (size 3.5) was reported from an unknown aspect/elevation. Late last week natural avalanche activity producing several 30 cm thick slabs in the latest snow was reported as well as lA large (size 3) storm slab avalanche was reported on a east aspect east of Terrace.

Snowpack Summary

Approximately 20-25 cm of new snow since Sunday morning brings settled storm snow accumulations to 50-80 cm over the past week. A freezing rain crust, 5-20 cm thick, was buried early February and can be found 10-40 cm below the surface on all aspects up to 1400 m. A weak layer buried  in mid-January is 100-140 cm below the surface and remains a concern. In most areas this layer is a crust, but it may also be surface hoar in sheltered areas at treeline and below. This layer produced a few human triggered avalanches throughout the region over the past week, and may remain reactive as it adjusts to the weight of the new snow.In thinner snowpack areas (north and inland), deeper crust / surface hoar layers that were buried in December and early January may still be a concern. They are buried over 150 cm below the surface, but may be triggerable from shallow spots.

Avalanche Problems

Storm Slabs

Significant snow and wind Tuesday night through Wednesday will form reactive storm slabs particularly at upper elevations and wind-exposed areas. Be aware that a storm slab release has the potential to step down to a deeper weak layer.
Be careful with wind loaded areas, especially near ridge crests and roll-overs.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2.5

Persistent Slabs

A weak layer exists 100-140 cm below the surface. It may still be possible for humans to trigger persistent slab avalanches on this layer, or for a storm slab release to step down to this layer resulting in a very large avalanche.
Caution around convexities or areas with a thin or variable snowpack.Minimize overhead exposure during periods of heavy loading from new snow, wind.Avoid lingering in runout zones. Large avalanches may run long distances.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2.5 - 4