Avalanche Forecast
Regions: Olympics.
We have already experienced a region-wide avalanche cycle such that the overall likelihood of wet snow avalanches has diminished. The expected significant cooling by Thursday will help lower the likelihood of wet snow avalanches. However, destructive wet slab avalanches remain a potential threat, being difficult to accurately predict. Extra caution is urged!
Detailed Forecast
Gradual cooling is underway as of Wednesday afternoon in the Olympics as a cooler trough approaches. Light to moderate showers at further lowering snow levels are expected Wednesday night and early Thursday.
Cool air should be over the area by Thursday with only scattered light showers expected as high pressure rebuilds over the area.
This weather will allow the previously wet snow pack to begin re-freezing and strengthening, causing an overall decreasing trend in the avalanche danger.Â
We have already experienced a region-wide avalanche cycle, such that the overall likelihood of wet snow avalanches has diminished. However, destructive wet slab avalanches are still being reported in isolated areas in the Cascades as of Wednesday. Realize that wet snow avalanches, specifically wet slab avalanches, are very hard to predict and demand an extra amount of caution when engaging with avalanche terrain.
The cooling trend through Thursday will lower the overall danger as surface snow begins to form a crust and liquid water continues to drain. Â
With that said, there remains a possibility of further wet slab avalanches, especially on unsupported slopes with a rock face bed surface.  These types of avalanches are highly unpredictable and not necessarily tied to peak warming or rainfall. Besides their huge destructive potential, wet slab avalanches often surprise backcountry travelers when they run further than expected.Â
Cornices have been weakened and prone to failure due to rain and mild temperatures. Very large cornices have been reported in many areas and have been involved in recent accidents and close calls. A cornice failure could trigger a large and destructive wet slab avalanche.
If you manage to venture into the above treeline zone Thursday, expect new or previous wind slab mainly on NW-SE aspects due to recent SW-W winds. Continue to watch for firmer wind transported snow on all aspects, especially in areas of complex terrain.
Snowpack Discussion
Weather and Snowpack
The first week or so of March was very cool and snowy. It looks like Hurricane had about 40-50 inches of snowfall during this period.
A strong frontal system brought increasing precipitation and winds along with a warming trend to the Olympics and Cascades on Thursday 3/9. On Thursday night rain fell  up to about 5000-5500 feet in the Olympics. Natural and skier triggered avalanches were reported on Friday 3/10.Â
Moist W-SW flow and a stalled frontal boundary have produced periods of moderate to occasionally heavy rainfall at most locations throughout the Olympics and the west slopes of the Cascades on Monday through Tuesday. Only light precipitation has fallen in the Hurricane Ridge area Wednesday between disturbances.Â
Recent Observations
The Hurricane NPS rangers reported that a snowboarder triggered a large cornice release on Friday 3/10 which in turn triggered a very large slab avalanche on the locally named Pit Bull path (NE aspect at about 5000 ft). NWAC is working on a blog post featuring photos of this avalanche incident. We hope to post online in the next few days.Â
A loose wet avalanche near the summit of Mt. Angeles in turn triggered a large slab avalanche on S-SE slopes at about 6000 ft. Other loose wet avalanches from S-SE slopes crossed the main road below the level of Hurricane Ridge on Thursday 3/9 or Friday 3/10.Â
Goat Creek avalanche where it crossed the road at about 3500 ft. Avalanche occurred 3/9 and the photo was taken 3/10. Photo by Dave Turner.
Avalanche Problems
Wet Slabs
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Unlikely
Expected Size: 1 - 2
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, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2