Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 27th, 2019–Dec 28th, 2019

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

Regions

South Coast Inland.

Light new snow amounts and wind are expected to form fresh wind slabs at higher elevations. In the north of the region, this adds a layer of complexity to a serious persistent slab problem. Danger in the south of the region is MODERATE and specific to wind slab concerns.

Confidence

Moderate - Uncertainty is due to the extreme variability of wind effect on the snowpack. We are confident about the possible sizes of avalanches, should one release; what is less certain is the likelihood of triggering.

Weather Forecast

Friday night: Mostly cloudy, light west wind, temperatures near -8 C.

Saturday: Mostly cloudy with scattered flurries developing later in the day and bringing 1-3 cm of new snow by morning. Moderate southwest winds, alpine high temperatures around -6 C in the north of the region, closer to -3 C in the south. 

Sunday: A mix of sun and cloud. Light southwest winds, alpine high temperatures around -2 C and freezing level rising to 900 meters.

Monday: Mix of sun and cloud. Light to moderate southwest winds, alpine high temperatures around -3 C.

Avalanche Summary

Avalanche observations have been on a declining trend since the widespread avalanche cycle observed last weekend. During that cycle, avalanches were reported to be running to valley-bottom in the north of the region, failing on deeply buried weak layers. See this MIN report of an avalanche involvement from last weekend for an example of this avalanche problem.

The possibility for large human-triggered persistent slab avalanches remains a serious concern at higher elevations in the northern half of the region (e.g., Duffey, Hurley, etc.) as these persistent weak layers continue to produce concerning snowpack test results and are expected to heal slowly. 

Snowpack Summary

5-10 cm of new snow has fallen on a weak interface with moderate west winds forming shallow, touchy wind slabs on lee features in the alpine. 

Below the surface, the storm at the end of last week brought over 120 cm of snow to the south of the region and about 40 cm to the north of the region. This snow is gaining strength, but conditions beneath this layer vary dramatically and, in some areas, highly problematic.

In the north of the region, the above-mentioned storm snow brought a critical load to a now 30-70 cm-deep weak layer from late November composed of sugary faceted grains and hard melt-freeze crust. This structure is a recipe for large and destructive avalanches and a problem that may persist for weeks to months. This problematic layer is largely absent in the south of the region.

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Persistent slabs have potential to pull back to lower angle terrain.
  • Avoid steep convexities or areas with a thin, rocky, or variable snowpack.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.