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Avalanche Forecast

Archived

Dec 11th, 2021–Dec 12th, 2021

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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Northwest Inland.

Recent storm snow and wind have combined to form slabs in wind exposed terrain that will likely remain sensitive to human triggering Sunday. Craft travel plans that keep you in wind sheltered zones and don't linger in avalanche paths.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

We’re slowly moving into a period of high pressure.

SATURDAY NIGHT: Trace of snow overnight with light southwest wind, freezing level at valley bottom.

SUNDAY: Broken cloud cover, freezing level at valley bottom, moderate to strong southwest wind, trace of snow possible.

MONDAY: Scattered cloud cover, freezing level at valley bottom, moderate to strong east/southeast wind, no significant precipitation expected.

TUESDAY: A few clouds at dawn with cloud cover increasing after lunch, freezing level at valley bottom, light southwest wind, no significant precipitation expected.

Avalanche Summary

This MIN from the Hankin Saturday has some great photos of natural avalanche activity above the cabin, this is the kind of terrain where we'd expect wind slabs to remain problematic Sunday.

Our field team found similar conditions on Friday at the Onion.

If you do head out in the backcountry, please share your observations to the Mountain Information Network!

Snowpack Summary

The region picked up 10 to 20 cm of new snow Friday afternoon into Saturday afternoon, with a bit of wind out of the south. Previous to this, the region has been pounded by winds which have formed fresh slabs in wind exposed terrain at and above treeline. In more wind protected terrain, the riding has reportedly been epic.

Below 1400m, a thin rain crust exists below this week's new snow. There have been reports of faceting around this crust with previous cold temperatures. A spotty surface hoar layer has been reported down ~100cm in the alpine and treeline. 

An early season crust can be found near the base of the snowpack. It has shown reactivity in the past week with large loads (explosives and cornice), creating large avalanches. We don't know how widespread this problem may be, but we are definitely keeping an eye on it, and would be avoiding large features and areas with thin to thick snowpack transitions.

Snowpack depth at treeline ranges from 150-200 cm, with higher values in the western part of the region, tapering to the east.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.

Problems

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.

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.