Avalanche Forecast

Issued: Jan 15th, 2013 9:57AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Persistent Slabs, Wind Slabs and Loose Wet.

ccampbell, Avalanche Canada

Sea To Sky.

Summary

Confidence

Good

Weather Forecast

Wednesday: Mostly clear with valley cloud possible in the morning. A temperature inversion is expected to bring treeline and alpine temperatures above freezing, while lower elevations should stay cold. Winds should be light to moderate from the northwest. Thursday: Low cloud in the morning changing to a mix of sun and cloud throughout the day as the temperature inversion weakens and lower elevations start to warm up with freezing levels as high as 2500m. Light to moderate northwesterly winds shifting to westerlies in the afternoon. Friday: A mix of sun and cloud and dry throughout the day. Freezing levels remaining at around 2500m.

Avalanche Summary

There are no new reports or observations of natural or human triggered avalanches in the past 2 days, and I suspect there were a lot of people in the mountains on the weekend. There was a size 2 accidentally triggered slab avalanche in the Spearhead Range on Thursday. A thin wind slab was triggered near ridge top on a relatively low-angle slope, which then stepped down to a weak layer approximately 100 cm deep lower on the slope. This avalanche is suspected to have released on the early January surface hoar layer.

Snowpack Summary

The snow surface consists of thin new wind slabs, a sun crust, moist snow, dry faceted snow, or large surface hoar depending on aspect, elevation, and time of day. Below this 40-70 cm of recent storm snow sits on a persistent weakness of surface hoar, facetted snow, and/or a crust buried at the beginning of January. Reports from last weekend include a Rutschblock Score of 3 down 52cm on a thin crust in the Whistler area, and hard compression test results on distinct surface hoar on a northeast facing open glade below treeline in the Chehalis (northwest of Hope). No significant weaknesses have been reported recently below this in the mid snowpack layers. Near the base of the snowpack, a crust/facet layer exists, which is now unlikely to be triggered, except perhaps by heavy triggers in steep, shallow, rocky terrain where more facetting has taken place.

Problems

Persistent Slabs

Warm temperatures and solar radiation will increase the probability of avalanches releasing on a buried weak layer of surface hoar, facets, and/or a crust, down 40-70 cm.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 5

Wind Slabs

Strong northerly winds have created new wind slabs in exposed lee and cross-loaded terrain features.

Be cautious as you transition into wind affected terrain.>Avoid freshly wind loaded features.>Avoid travelling in areas that have been reverse loaded by winds.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Loose Wet

Loose wet activity is expected as temperatures rise. A loose wet slide could step down and trigger weaknesses deeper in the snowpack.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Jan 16th, 2013 2:00PM