Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 26th, 2019–Dec 27th, 2019

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

Make cautious terrain choices, buried weak layers are getting stressed by new snow and could produce large avalanches.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

THURSDAY NIGHT: Snow flurries with 5-10 cm of snow, 30-50 km/h wind from the west, alpine temperatures drop to -5 C.

FRIDAY: Scattered flurries with 5-15 cm of snow, 30-50 km/h wind from the southwest, alpine high temperatures around -2 C.

SATURDAY: Snow, heavy at times, 15-30 cm, 40-70 km/h wind from the south, alpine high temperatures around -1 C with freezing level up to 800 m.

SUNDAY: Scattered flurries with 5-10 cm of snow, 30-40 km/h wind from the south, alpine high temperatures around -3 C.

Avalanche Summary

Recent avalanche activity has been limited in size 1-2 avalanches in the uppermost layers of snow (storm slabs and wind slabs), however ongoing snowfall is adding stress to buried surface hoar layers. Even though no recent avalanches have been reported on these persistent weak layers, they could be reaching the tipping point for producing large avalanches.

On Thursday a few size 1-2 wind slabs were triggered naturally and with explosives. Similar activity has been reported during each snowfall event over the past week.

Snowpack Summary

10-30 cm of recent snow has been blown around by moderate to strong southwest wind. 20-40 cm of recent snow overlies a thin layer of surface hoar and a total of 40-80 cm of snow now overlies a more prominent weak layer of surface hoar, old faceted surfaces, and/or a crust on south/southwesterly alpine slopes. This more prominent surface hoar layer has been reactive in snowpack tests, providing evidence it is at a tipping point where any additional load (such as a person) could trigger an avalanche on this layer. Heavy snowfall could easily overload this layer. Reports from the Shames area suggest the surface hoar layer is on all aspects, but more prevalent on southeast to southwest aspects around 800-1400 m, and more likely in leeward and sheltered alpine areas. The lower snowpack is generally considered strong.

Terrain and Travel

  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.