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Avalanche Forecast

Archived

Dec 10th, 2021–Dec 11th, 2021

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

Regions

North Rockies.

The best riding will be found in sheltered areas treeline and below. Avoid overhead hazard and watch for signs of instability such as whoomphing, shooting cracks, and hollow sounds.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Snowfall beginning on Friday evening will continue into the day on Saturday. Later in the weekend is looking quieter with the potential for some clearing.

Friday Overnight: As a strong pacific system passes over the northwest ranges we will see winds increasing overnight along with rising freezing levels, and moderate snowfall. Southwest winds will be strong to extreme at ridgetop, easing to strong into the morning. Freezing levels rise to around 1200m, with 10-30 cm of new snow. 

Saturday: A cloudy day with continued snowfall. Strong southwest winds at ridgetop with accompany 5-20 cm of new snow throughout the day. Freezing levels hovering at 500m with alpine temperatures around -10 C.

Sunday: Partially cloudy with flurries, accumulation up to 10 cm. Moderate to strong southwest winds at ridgetop with alpine temperatures around -15 C. 

Monday: A quieter day with a mix of sun and cloud, light flurries and light to moderate ridgetop winds from the southeast. Alpine temperatures around -15 C.

Avalanche Summary

There have been very limited reports in the past week! If you do head out in the backcountry, please share your observations/pictures/conditions to the Mountain Information Network! Thank you :)

Snowpack Summary

Another 10-30 cm overnight brings this week's new snow totals to 40-60 cm. This new snow came in with strong winds from the southwest, which will be redistributing the new snow into wind slabs in the alpine and exposed areas at treeline. In sheltered areas, the new snow will behave as a storm slab or loose dry problem, particularly where it overlies a crust.

There is still some concern for buried weak layers. Surface hoar has been observed in sheltered areas at treeline and below, now buried under this week's storm snow. The November 27th rain crust is buried 40-100cm and exists up to 1500m in some areas. 

The lower snowpack consists of a series of early season crusts. Cold temperatures will have promoted faceting around these crusts. Shallow alpine slopes along the eastern side of the Rockies towards Jasper may have weaker, faceted snow near the ground. 

Snowpack depths at treeline range from 60cm-200cm, with the shallower value mainly in the eastern side of the range. The alpine snowpack ranges from 150cm-200cm. 

Terrain and Travel

  • Choose conservative terrain and watch for clues of instability.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

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.