Avalanche Forecast
Regions: Olympics.
Watch for shallow wet snow conditions where shower activity may be greater. Continue to avoid cornices and areas below where glide avalanches could be a problem.
Detailed Forecast
A somewhat unstable southerly flow pattern will maintain the possibility of showers Friday, especially during the afternoon. Most areas should only receive light showers. Freezing levels will gradually lower Friday but much of the shower activity should be rain below about 7000 feet.
The cooling will have the effect of solidifying the moist to wet upper snow layers, leading to a decreased danger of wet snow avalanches. 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 much new snow instability, nor should there be enough rain in the mid elevations to cause too significant of increase there. The fact the upper snowpack is fairly well drained at this point, it should be able to quickly drain the water received from showers.Â
Small loose-wet avalanches should remain possible Friday on steeper slopes. Watch for wet surface snow getting deeper than your boot tops, mainly where shower activity is heaviest. Triggered loose wet avalanches should be most likely on steep solar slopes, but could be seen on any steep aspect in this mild showery pattern. Watch for terrain traps that might funnel even shallow, loose snow, such as gullies and creeks.Â
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.
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Snowpack Discussion
Weather and Snowpack
In a word, HOT! Well, maybe two, Hot & Melting.
Freezing levels have been near or well over 10,000 feet for the past five days with strong spring sunshine. This is the third period in April with freezing levels above 10,000 feet and that has helped establish good melt water draining in the snowpack with much of the lower elevation snow continuing to melt away, transitioning to a spring snowpack. The last snowfall of 4-8 inches is now a thing of the distant past, having fallen late last week and assimilated into the upper melting surface layers.
Storms in March built unusually large cornices along many ridges. While these have been melting back, many have also failed recently, producing wet snow avalanches on slopes below during this recent warm weather. Cornices should remain a main concern over the near future. The potential for low probability/high consequence encounters, such as cornice failures and glide avalanches from steep unsupported slopes and smooth rock faces, should continue this spring.Â
The mid snowpack should generally be a stable mix of crusts and layers of moist and rounded snow crystals.
The lower elevation snowpack is rapidly melting away and in many areas is now gone!
Recent Observations
The last observations in the Hurricane Ridge area from Matt Schonwald last Saturday was indicating there was no longer enough snow in the below treeline band to be an avalanche problem and even within the near treeline band, avalanches were confined to specific terrain features.Â
After another week of very hot weather, the melt back of the snowpack has continued to diminish the threat of avalanches in this area.
Watch for cornices and possible shallow wet snow conditions in areas that are maintaining a more significant snowpack.
Avalanche Problems
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.
Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1