Avalanche Forecast

A weakening cold front should bring a brief period of light rain and snow Monday night, with the rain/snow line into the above treeline terrain. Further cooling should follow the front and rain/snow showers will re-develop behind the front during the day Tuesday and light to moderate SW crest-level winds will transport the new snow as it accumulates. The old snow surfaces are expected to begin to refreeze at higher elevations as temperatures cool. New snowfall on Tuesday is anticipated to bond well to the refreezing snow surfaces.

Watch for the development of shallow wind slabs, particularly on NW through SE aspects above treeline. Monitor new snow and wind transport diligently throughout the day and avoid wind-loaded slopes.

Note that a variety of snow conditions may be encountered on Tuesday, including breakable crusts, wet snow, new snow over refreezing surfaces, etc.

Inversion conditions since the last storm have enabled the initially dry snow at higher elevations to undergo 3 days of melt-free cycles, forming crusts of variable thickness on most aspects at night and wet snow surfaces during the day. At lower elevations, snow was previously saturated, but here temperatures have remained near or slightly above freezing within the inversion layer.

Surface hoar up to 1 cm has been observed in some locations, such as Blewett Pass, on non-solar slopes during this period.

Last week’s storms brought 8-14 inches of snow to the east slopes of the Cascades. Winds throughout the storm period redistributed snow, forming wind slabs on a variety of aspects especially in exposed terrain that continue to strengthen over the past several days.

A supportive crust (1/5) formed from a widespread freezing rain event in the central-east zone, extending to the Stevens and Snoqualmie Pass areas. This layer is not present in the northeast from Washington Pass to Holden.

Snowdepth still decreases substantially east of the Cascade crest. In many areas below treeline, there has not been enough snow to present an avalanche danger.

Observations

North

North Cascades Heli was in the field Saturday and observed thin wind slabs, 8 inches thick on lee slopes. Roller balls were reported on sunny slopes in the afternoon, but natural loose wet avalanche was not observed.

Guides from both North Cascades Mountain Guides and North Cascades Heli were in the field Friday. Observations suggest storm snow weaknesses are gaining strength.

Central

Mission Ridge Pro Patrol Friday reported upside-down new storm snow. Avalanches observed failed within the storm snow.

Older but still relevant observations:

Several observations from the Mission Ridge and Blewett Pass areas have reported 2-3mm facets on the ground, including a recent post found here. Another report near Mission ridge found a facet layer 45 cm above the ground. These layers will need to be monitored as they could develop into potentially dangerous weak layers in the future.

South

No recent observations