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Avalanche Forecast

Archived

Jan 1st, 2020–Jan 2nd, 2020

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 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, human triggered possible.

Regions

Northwest Coastal.

Watch for windslabs formed by strong winds on Wednesday. Fresh slabs on south facing slopes will be especially sensitive to solar triggering when the sun comes out on Thursday.

Confidence

Moderate - Uncertainty is due to the extreme variability of wind effect on the snowpack. Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Wednesday night: Cloudy with scattered flurries bringing 10-15 cm of new snow. Strong west winds.

Thursday: Sunny periods with cloud increasing and flurries beginning in the evening. Light variable winds. Alpine high temperatures around - 10.

Friday: Cloudy with flurries bringing 10-20 cm of new snow, totaling 20-40 cm with overnight accumulations, easing overnight. Light northeast winds. Alpine high temperatures around -5.

Saturday: Cloudy with continuing flurries bringing 5-15 cm of new snow, continuing overnight. Light southwest winds. Alpine high temperatures around -8.

Avalanche Summary

A large natural storm slab avalanche cycle up to size 3.5 was reported in Bear Pass earlier this week. The cycle has subsided as a cooling trend set in late Wednesday, locking up the previously moist storm snow. The large loads provided by this cycle were a great test for reactivity of the persistent slab problem. An absence of reports of storm slab avalanches stepping down to the deeper layers indicates that the deep persistent slab may no longer be an avalanche problem. 

With the forecast snow and strong wind over Wednesday night, thin, touchy wind slab forming over a crust will be the main concern. Also watch for solar triggering of newly fallen snow on steep south facing terrain features in the alpine.

Snowpack Summary

10-15 cm of new snow fell amid strong winds and cooling temperatures Wednesday night onto a temperature crust at all elevations except the very high alpine. Below the well settled slab of recent storm snow, two layers of surface hoar are buried 70-150 cm deep. Reports from the Shames area suggest buried surface hoar can be found on all aspects, but is more prevalent on southeast to southwest aspects around 800-1400 m. Avalanche activity on this layer has not been reported for the past week, indicating that it has become dormant.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Closely monitor how the new snow is bonding to the crust.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.

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.