Avalanche Forecast

Issued: Jan 31st, 2020 5:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs and Persistent Slabs.

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Storm slabs and wind slabs are failing where new snow accumulations are greater than 25 cm and moderate winds are ongoing. The best riding will continue to be in wind protected areas without overhead hazard.

Summary

Confidence

Moderate - Uncertainty is due to limitations in the field data. Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region.

Weather Forecast

Friday Overnight: 5 to 15 cm of snow with moderate southwest wind. Temperature around -10 C. 

Saturday: Trace (in the east) to 10 cm (in the west) of snow with moderate gusty west wind. Temperatures around -12 C in the mountains.

Sunday: Mix of sun and clouds. Dry. Moderate gusty west wind. Slightly cooler temperatures in the minus mid-teens.

Monday: Flurries to 10 cm of snow. Steady temperatures around -15 C. Moderate SW winds.

Avalanche Summary

In deeper snowpack areas where the storm snow is 30 cm or more storm slabs were reactive to human triggering on small slopes. In these same areas natural avalanches were heard but not seen (due to poor visibility) meaning there was a natural avalanche cycle with size 2 to 3 avalanches, most likely triggered by wind loading. 

Snowpack Summary

Widespread wind and storm slabs where up to 50 to 70 cm storm snow accumulated with strong winds. Below the new snow is a weak layer of facets that developed in the mid-January arctic outflow event. At treeline, a suspect layer of surface hoar may be found 1 m below the surface. Below treeline the new snow rests on a melt-freeze crust and a well settled snowpack.

A deep crust/facet layer lurks at the base of the snowpack, especially in shallower (eastern) areas that was reactive earlier in January. While it is promising that last week's snowfall did not trigger avalanches on this deep persistent weak layer, there is a lingering uncertainty whether this week's weather could cross a threshold. Triggering this layer is most likely in shallow, rocky start zones or with a large load such as cornice failure or rapid loading from snow and wind.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Storm Slabs

An icon showing Storm Slabs

Strong and gusty winds with new snow are building reactive storm slabs on all aspects where more than 25 or 30 cm has accumulated. Similarly there are deeper touchy wind slabs on northwest through east facing slopes. 

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

A layer of weak, faceted snow from the January cold snap is now buried 40-70 cm deep. The continued snowfall and wind continues to load this persistent weak layer, potentially bringing it to its tipping point.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2.5

Valid until: Feb 1st, 2020 5:00PM