Avalanche Forecast
Issued: Jan 28th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Cornices and Deep Persistent Slabs.
ahanna,
Avalanche Canada
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.
Summary
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 slabs will form above 1000 m where snowfall accumulates. Upwards of 30 cm is expected for most areas, around 10 cm for Whistler. Strong southwest winds will form deep wind-loaded pockets in lee features at alpine and treeline elevations.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Cornices
Mild temperatures, strong winds and new snow have been a recipe for significant cornice growth recently.
Aspects: North, North East, East, West, North West.
Elevations: Alpine.
Likelihood
Expected Size
Deep Persistent Slabs
As recently as Tuesday, explosives testing continues to periodically trigger a weak layer of snow at the bottom of the snowpack. This deep persistent layer has proven that if triggered, it will produce very large and destructive avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 29th, 2020 5:00PM
