Avalanche Forecast

Issued: Apr 22nd, 2018 3:33PM

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

jlammers, Avalanche Canada

Sea To Sky.

Warming and solar radiation will drive the avalanche danger in the coming days. Watch for conditions that change throughout the day, and be cautious of overhead hazards.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A ridge of high pressure will develop for the forecast period bringing sunny skies and light ridgetop winds. The freezing level will hover around 2800m on Monday and then rise to about 3500m for Tuesday and Wednesday.

Avalanche Summary

On Saturday explosives control produced numerous wind slab avalanches mainly in the size 1.5 range in lee alpine and treeline terrain. Loose wet avalanches and cornice falls are expected to become problematic with warming and solar radiation forecast for this week. Warming also has the potential to wake-up the late March crust interface with the possibility of surprisingly large and destructive avalanches.

Snowpack Summary

New snow and wind on Saturday formed fresh wind slabs in upper elevation lee terrain. The new snow overlies settled storm snow on shaded aspects above 2000m and a melt-freeze crust in most other areas.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 140 cm below the surface. This layer is spotty in its distribution and has recently produced large and destructive avalanches. It is most likely to be problematic on west, north, and east aspects between 1900 m and 2250 m. I'd continue to treat this layer very cautiously and would anticipate increase reactivity at this interface with warming forecast for the next few days.The mid and lower snowpack are well-settled and strong.

Problems

Loose Wet

Warming and solar radiation are expected to trigger loose wet avalanches, especially in steep, sun-exposed terrain. Loose wet avalanches can be pushy and entrain mass quickly. Warming may also trigger destructive cornice failures.

Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Use caution above cliffs and terrain traps where small avalanches may have severe consequences.

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Persistent Slabs

Professionals are traveling cautiously in shaded upper treeline and alpine terrain due to a weak layer buried 60 to 140 cm below the surface. Forecast warming and cornice failures will likely re-activate this destructive interface in isolated terrain

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Pay attention to overhead hazards like cornices, which could trigger persistent slabs.Be aware of the potential for wide propagation due to the presence of buried weak layers.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

New snow and strong winds from Friday night have formed new wind slabs in upper elevation lee terrain. Although they're likely to gain strength quickly, I'd remain cautious around ridge crests and in gullies.

Be cautious as you transition into wind affected terrain.Stay off recent wind loaded areas until the slope has had a chance to stabilize.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 23rd, 2018 2:00PM