Archived

Avalanche Forecast

Dec 9th, 2017–Dec 10th, 2017

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Northwest Inland.

New snowfall amounts are uncertain for Sunday. Pay close attention to how much new snow falls in your area.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Sunday

Weather Forecast

Saturday night: 2-15cm of new snow with rain at lower elevations / Strong to extreme southerly winds / Freezing level at 1300mSunday: 0-3cm of snow / Strong to extreme southerly winds / Freezing level at 2400mMonday: Clear skies / Strong to extreme southerly winds / Freezing level at 2400mTuesday: Trace amounts of new snow / Light variable winds / Freezing level at 1200m

Avalanche Summary

No new avalanches have been reported, however it is expected that warm alpine temperatures and sunshine initiated natural activity on steep solar aspects at higher elevations on Thursday and Friday. Looking forward, expect any new snow accumulations to bond poorly with the crust and surface hoar that form our current snow surface.

Snowpack Summary

Average snowpack depths now total 80-140 cm at treeline elevations and up to 160 cm in the alpine. (Depths of up to 210 cm have been reported from the Howsons.) Solar and temperature crusts are expected to have formed on the wind-affected surface at higher elevations on Thursday. Below the surface, Approximately 30-50 cm of storm snow now overlies two crusts that were buried near the end of November. These crusts are widespread and extend into the alpine. Although snowpack tests have previously shown hard results at these crust interfaces, more recent observations have been limited. Below these crusts, a well settled mid-pack overlies the late October crust near the base of the snowpack. This "crust/facet combo" layer is widespread and has been reactive to rider and remote triggers. It also continues to produce sudden snowpack test results.

Avalanche Problems

Wind Slabs

New snow and wind on Saturday night may form fresh wind slabs in higher elevation lee terrain. New wind slabs may have a poor bond to the underlying snow, especially in areas where buried crusts exist.

Avoid steep convexities or areas with a thin or variable snowpack.If triggered, wind slabs may step down to deeper layers and result in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2

Deep Persistent Slabs

The late October crust lies near the base of the snowpack with a thin layer of weak, sugary snow above it. This layer should be on a strengthening trend, but a heavy trigger in a thin snowpack area may still be enough to cause it to react.

Be especially cautious in shallow snowpack areas where triggering a deeper layer may be easier.Be aware of the possibility for full depth avalanches due to deeply buried weak layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3