Avalanche Forecast

A frontal system passing through the Cascades Saturday night will bring light amounts of new snow to mid and higher elevations late Saturday night through Sunday. The avalanche forecast will slightly differ by zone based on expected new snow amounts, with the most snow expected in the northwest Cascades but little new snow expected along the east slopes of the Cascades.  

Shallow storm slabs are possible mainly above treeline Sunday. Due to the refreezing snow surface and a cooling trend, new snow should generally bond well to wet snow or rough surface crusts. However, due to the showery regime in the cold air mass overhead Sunday, graupel layers are a probable bed surface for shallow storm slabs. Wind slab will not be specifically listed, but with light to moderate westerly transport winds, expect some loading on lee slopes above treeline.   

Due to the cooling trend and cloudy skies expected, small loose wet avalanches should be unlikely except on isolated steep slopes at lower elevations or during sunbreaks on solar aspects. Watch for terrain traps that might funnel even shallow, loose snow, such as gullies and creeks. 

The potential for cornice releases will diminish, but still remain a possibility through the weekend. Cornice releases are very unpredictable, so avoid areas below cornices and remember that cornices can break much further back than expected along ridges.

Although not listed as an avalanche problem, powerful glide avalanches can release unexpectedly so also avoid areas below steep unsupported slopes or rock faces, especially if they are showing glide cracks.

Weather and Snowpack

On Friday we began our slow transition from unusual April warmth to a cooler and unsettled pattern. Saturday featured mostly cloudy skies and occasional light showers for the west slopes of the Cascades, Olympics and Mt. Hood area while the eastern slopes away from the Cascade crest saw mostly sunny skies. 

For most of last week, freezing levels had averaged near or above 10,000 feet with strong spring sunshine. This was the third period in April with freezing levels above 10,000 feet. The cumulative effect of the warm stretches have helped establish good melt water drain channels in the snowpack with much of the lower elevation snow continuing to melt away and generally transitioned us to a homogeneous spring snowpack throughout the region. 

Storms in March built unusually large cornices along many ridges. While these have been melting back, many have failed recently, producing small and large wet snow avalanches on slopes below during the recent warm weather. The potential for low probability/high consequence encounters, such as cornice failures and glide avalanches from steep unsupported slopes and smooth rock faces, will continue this spring. 

The mid and lower snowpack should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

WSDOT avalanche professionals working in the Chinook Pass area last week have, as expected under the hot weather, produced numerous small to moderate sized loose wet avalanches. The upper layers of the snowpack appear to be draining well and with daily melt-freeze cycles, avalanches have mainly involved the upper surface layers of snow up to about the top 6 inches. There were several natural cornice releases noted Tuesday and Wednesday, each producing wet slides on the slopes below. 

NWAC observer Lee Lazzara covered a great deal of terrain in the Mt Baker backcountry earlier this week and noted similar conditions with all avalanche problems being heat related; cornices, glide avalanches on unsupported terrain features and small loose wet avalanches during the warm part of the day. The snowpack is quickly melting back in much of the terrain below treeline, making travel choices difficult for some lower elevation areas. Dallas Glass traveled above treeline out of Paradise Wednesday, and found that glide cracks were evident on a variety of aspects and elevations but no new releases. Laura Green toured in the Salmon River drainage of Mt. Hood Thursday and found a supportable melt-freeze crust slowly breaking down during the day near and above treeline and no significant avalanche concerns. Laura observed a fracture line of one large avalanche in the White River drainage that had likely occurred mid-week during the warm spell around the 9000 ft level. 

Several west-side ski areas operating Saturday 4/23 noted no avalanche concerns under the cooler and cloudier conditions.