Avalanche Forecast

The slow cooling trend will continue Saturday with more cloud cover and light showers expected for the Olympics, west slopes of the Cascades and Mt. Hood. East of the Cascade crest more sunshine is expected especially earlier in the day.  

The cooling will have the effect of solidifying the moist to wet upper snow layers, leading to a decreased danger of wet snow avalanches especially above treeline. However, any additional water from showers will maintain some wet snow conditions. All in all, there should not be enough new snow in the above treeline band to cause concerns about new snow instability, nor should there be enough rain in the mid and lower elevations to cause a significant increased risk of wet snow avalanches. The fact the upper snowpack is now fairly well drained as a result of the extended warm weather, it should be able to quickly drain the water received from showers, minimizing the threat of larger wet snow avalanches. 

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

The potential for cornice releases will likely 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 wetter pattern featuring mostly cloudy skies, showers, and a few thunderstorms that sparked along the east slopes of the Cascades and traveled northwestward over the Cascade crest. 

Leading into Friday, freezing levels had averaged near or above 10,000 feet since last Sunday and was accompanied by 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 draining in the snowpack with much of the lower elevation snow continuing to melt away and an overall transition to a homogenous spring snowpack. The last snowfall is no longer relevant, having fallen over a week ago and has since assimilated into the upper surface layers.

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 earlier this 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. Those being 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.