Avalanche Forecast
Regions: Cascades - East.
Watch for fresh wind slab on lee slopes in steeper terrain primarily above treeline. Sunbreaks can quickly create loose wet avalanche conditions on steeper solar aspects. Give cornices a wide safety margin.
Detailed Forecast
A cool upper trough will sit over the Pacific Northwest on Friday with shower activity increasing in the afternoon and evening. Sunbreaks are most likely during the morning through mid-day before convective clouds build in the afternoon.  Â
Watch for firmer wind transported snow, mainly on NW-SE slopes and above treeline on Friday. Fresh wind slab may have locally bonded poorly to graupel layers received Thursday.Â
After a cool night Thursday, snow levels will remain low on Friday. This should generally restrict the loose wet potential to the shallow amounts of new snow found on steeper solar aspects near and below treeline. This time of year even brief sunbreaks combined with subtle daytime warming can quickly activate loose wet avalanches.Â
Recent cornices are very large and resulting slab avalanches are dangerous and unpredictable. There have been numerous recent cornice failures with some being very large in the Washington Cascades. Five people were tragically killed by a cornice release in British Columbia on Saturday. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below large cornices. See a blog post regarding cornices here.
Snowpack Discussion
Weather and Snowpack
Warmer temperatures with periods of rain received in mid March has left behind a well consolidated snowpack with one or more strong melt freeze crusts in the upper portion of the snowpack in the near and below treeline elevation bands.Â
A series of strong spring storms occurred during the first week of April.
A front crossed the Northwest on Sunday night and Monday, depositing up to a few inches of snow along the east slopes of the Cascades. Moderate winds built fresh wind slabs above treeline on steep lee terrain features.
Mostly sunny weather Tuesday helped storm snow to begin to settle, however, winds remained strong enough above treeline Tuesday to continue to transport surface snow.Â
A weather system passing through the area Wednesday night produced roughly half an inch of water across east slopes of the Cascades through Thursday morning. This likely translated into a few inches of new snow around 4000 feet with slightly higher amounts above 6000 ft. Showers increased during the day on Thursday with light additional snow accumulations mixing with graupel during more intense showers.Â
Recent Observations
North
No recent observations.
Central
Tom Curtis was on Irving Peak near Poe Mountain, NE of Lake Wenatchee on Wednesday, 4/12. There was about 6-8 inches of recent storm snow over the most recent melt-freeze crust on shaded slopes. This snow became moist to wet through the day and with little effort produced rather large loose-wet avalanches, even on steeper N-NE aspects. Several large to very large loose wet slides were observed and heard across the valley, releasing on N-NE facing terrain on Nason Ridge, including higher elevation band above treeline. Cornices were also very large. These conditions limited any travel on steep terrain of consequence.
South
No recent observations.
Avalanche Problems
Wind Slabs
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
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: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
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, Treeline.
Likelihood: Unlikely
Expected Size: 1 - 2