Avalanche Forecast

Moderate - Intensity of incoming weather systems is uncertain

FRIDAY: Mostly cloudy with intermittent snowfall, moderate westerly winds, alpine temperature near -8 C, freezing level below valley bottom.SATURDAY: Mostly cloudy with intermittent snowfall, moderate westerly winds, alpine temperature near -5 C, freezing level near 1000 m with possible inversion conditions.SUNDAY: Partly cloudy with valley cloud, light to moderate westerly winds, alpine temperature near 0 C, freezing level near 1300 m with inversion conditions.

A widespread avalanche cycle was observed on Tuesday through Thursday. Numerous large natural avalanches (size 3 to 3.5) were triggered in the alpine and ran to near the valley floor and numerous size 2 avalanches started at and below treeline. Operators also reported numerous large human, vehicle, and remote-triggered avalanches.  Some of these avalanches ran on relatively shallow slope angles (around 30 degrees) and in fairly dense trees.  Expect continuing avalanche activity because of the touchy snowpack.

The snowpack reached its tipping point on Tuesday and Wednesday as warming and precipitation combined to overload buried persistent weak layers in the snowpack and create a large natural avalanche cycle.Over 100 cm of snow has fallen in the past few days.  The snow fell relatively warm with moderate winds, which has formed storm slabs.  The snow also formed large cornices.  Deeper in the snowpack, an unstable weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below treeline elevations.  Below, a rain crust that developed late-November with associated sugary facets are also being stressed. Snowpack test results show sudden fracture characters and high propagation potential for both of these buried layers, indicating that they can be triggered and could propagate into large, destructive avalanches. This has been the case, as shown in the Avalanche Summary.