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

Jan 28th, 2020–Jan 29th, 2020

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

Regions

Sea To Sky.

Avalanche danger will increase through the day Wednesday as new snow and strong winds form reactive storm slabs. Where new snow depths exceed 40 cm, avalanche danger will rise to HIGH for alpine and treeline elevation bands.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Tuesday night: Mostly cloudy with flurries starting, bringing up to 5 cm new snow. Alpine low -8 C. Southwest winds building to strong. Freezing level 1000-1400 m.

Wednesday: Snow, upwards of 30 cm for most areas, around 10 cm for Whistler. Alpine high -3 C. Strong southerly winds, approaching extreme southwest at ridgetop. Freezing level 1100-1300 m.

Thursday: Increasing cloud with flurries starting in the afternoon bringing 10-20 cm new snow. Alpine high 0 C. Light to southwest winds increasing to strong in the afternoon. Freezing level 700 m rising to 1800 m.

Friday: 30-60 cm new snow with rain below 1500 m. Alpine high + 1 C. Strong southwest winds, approaching extreme at ridgetop. Freezing level 1900 m.

Avalanche Summary

Explosive control work Sunday through Tuesday produced mostly size 1 storm slabs and size 2 cornices with up to 75 m wide propagation. Natural windslab and cornice failures up to size 2.5 were observed in the Whistler backcountry on lee and cross-loaded alpine terrain.

The deep persistent problem again reared its head on Monday with large explosive loads producing a size 2.5. in shallow, rocky terrain.

Snowpack Summary

A variety of wind-affected surfaces exist in alpine and open treeline areas. Exposed windward slopes are scoured down to the January 20 crust. On leeward terrain, surface snow has been pressed into slabs over the crust, and notable cornice growth has been observed at ridgetops. Below treeline, fluctuating freezing levels have left a combination of moist snow and crusts.

Weak faceted grains and crusts near the base of the snowpack continue to be a concern in inland parts of the region such as the Spearhead Range.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Extra caution is needed around cornices under the current conditions.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.