Sea to Sky Avalanche Forecast

Issued: Mar 16th, 2020 4:00PM

Tue Mar 17th Current Conditions
Alpine Moderate Treeline Moderate Below Treeline Moderate
Wed Mar 18th 2 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Low
Thu Mar 19th 3 Day Outlook
Alpine Moderate Treeline Moderate Below Treeline Low

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

Avalanches will become more likely as the snow heats up. Be very cautious around cornices and large slopes getting hit by the sun.

Summary

Confidence

High - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

A ridge of high pressure brings clear dry conditions for the week.

MONDAY NIGHT: Clear skies, light northwest wind, freezing level drops to valley bottom with alpine temperatures dropping to -8 C

TUESDAY: Sunny with a few clouds, light northeast wind, freezing level climbing to 1500-1800 m in the afternoon, alpine high temperatures around -2 C.

WEDNESDAY: Clear skies, light northeast wind, freezing level climbing to 1500 m, alpine high temperatures around -2 C.

THURSDAY: Sunny with a few clouds, light wind, freezing level climbing to 1500 m, alpine high temperatures around -2 C.

Avalanche Summary

Over the weekend a few small (size 1) human triggered slabs were reported, primarily wind slabs in alpine terrain.

Looking forward, the warming trend poses a number of avalanche concerns including loose wet avalanches, cornice falls, and an increasing potential for the deep persistent slab problem to reawaken. The potential for triggering wind slab avalanches also remains possible in steep alpine terrain.

Snowpack Summary

Surface conditions are highly variable with a mix of crusts, moist snow, and hard wind slabs. The surface will become moist on sun-exposed slopes and at lower elevations throughout the day. The warm air coupled with strong radiation from the sun has potential to rapidly weaken the upper snowpack and cornices.

In the alpine, hard wind slabs may be found on all aspects due to variable wind directions. Recent wind has blown from the northeast, forming wind slabs in unusual south to southwest terrain features. In sheltered terrain, about 30 cm of settled snow may overly a melt-freeze crust and potentially small surface hoar crystals.

Weak faceted snow and melt-freeze crusts exist near the base of the snowpack in some of the region, particularly the eastern and northern parts. This layer is considered dormant, as it hasn't produced an avalanche since Feb 20. The likelihood of triggering this layer may increase during this warming trend.

Terrain and Travel

  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Carefully evaluate steep lines for wind slabs.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

Problems

Loose Wet

An icon showing Loose Wet

Likelihood

Likely

Expected Size

1 - 2

Another day of warm weather will destabilize surface snow. The most warming will occur on sun-exposed slopes during the heat of the day, but be suspect of any steep slope that may be heating up, especially if you notice moist snow. Cornices will also weaken with the warming trend. 

Aspects:

East, South East, South, South West, West.

Elevations:

All elevations.

Wind Slabs

An icon showing Wind Slabs

Likelihood

Possible

Expected Size

1 - 2

Triggering wind slab avalanches remains possible after strong northeast wind formed slabs in atypical terrain features last week. These slabs could remain touchy, as they may overly a weak layer of surface hoar.

Aspects:

All aspects.

Elevations:

Alpine.

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Likelihood

Unlikely-Possible

Expected Size

3 - 4

There is uncertainty on whether the weak faceted grains and melt-freeze crusts near the base of the snowpack are still a problem or not. This may vary for mountain to mountain. Should this basal weak layer exist where you travel and be triggered, the consequence of it would be devastating. The most likely spot for a human to trigger it would be in thin rocky terrain. A cornice fall also has the potential of triggering it. The likelihood of avalanche activity on this layer may increase during this warming period.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Mar 17th, 2020 4:00PM