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Archived

Avalanche Forecast

Dec 18th, 2017–Dec 19th, 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
2: Moderate
The avalanche danger rating below treeline will be moderate
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

Regions: Kootenay Boundary.

Touchy conditions persist in the wake of Sunday night's big dump of snow. The combination of more new snow, strong winds and a buried weak layer are a recipe for elevated danger ratings.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Another significant storm arrives Tuesday into Wednesday, delivering another big wallop of precipitation. Fasten your seat belts folks!TUESDAY: Snow. Accumulation 15-20 cm during the day with another 15-20cm overnight. Ridge wind moderate from the southeast. Temperature near -6. Freezing level 500 m. WEDNESDAY: Cloudy with lingering flurries. Ridge wind moderate northerly. Freezing level at the surface.THURSDAY: Cloudy with isolated flurries. Accumulation of 5-10 cm possible. Ridge wind moderate from the west. Temperature near -7. Freezing level at the surface.

Avalanche Summary

On Monday, numerous storm slabs up to Size 2 were reported in the Nelson area: They were either easily triggered by skiers or ran naturally. Also on Monday, several classic signs of instability (whumphing, shooting cracks, easy sudden results in snowpack tests) were reported near Nelson. See here for the great MIN report.

Snowpack Summary

The Nelson area and points farther south saw 20-30 cm of new snow in Sunday night's storm, with moderate to strong winds. Snow drifts as deep as 60cm have been reported and we also received word that the upper snow pack is 'upside down' (heavier, denser snow on top of lighter snow).All this new snow has fallen on a variety of old snow surfaces, depending on aspect and elevation. On solar aspects a thin melt-freeze crust has been buried. On northerly aspects, feathery, surface hoar crystals (10-60 mm in length) have been buried below treeline as well as protected areas at treeline. In the alpine the old surface consisted of sugary snow (facets) and hard, wind scoured snow. Below the crust layer the lower snowpack is moist and well settled.

Avalanche Problems

Storm Slabs

Conditions are expected to remain touchy with the new snow sitting on a weak surface hoar layer in many locations. Heavy snowfall on Tuesday into Wednesday will only make it worse.
Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 3