Avalanche Forecast

Archived

Apr 5th, 2017–Apr 6th, 2017

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

.

Loose wet avalanches should be seen in all areas in the near and below treeline bands or on solar aspects during periods of extended sunshine. New storm and wind slab problems will be shallow and primarily be found above treeline for the central-west and southwest Cascades.

Detailed Forecast

A stalled frontal boundary oriented north-south and to the west of the Cascades will finally lift to the northeast and out of the area Thursday morning. After a period of light to moderate rain and snow, post-frontal showers, heaviest in the Mt. Baker area will follow in the afternoon. More sunshine should mix in for the central-west and southwest Cascades in the afternoon.

Loose wet avalanches should be seen in all areas in the near and below treeline bands or on solar aspects during periods of extended sunshine. Watch for wet surface snow deeper than a few inches, pinwheels and initial natural releases that indicate an increasing loose wet avalanche danger.

New storm and wind slab problems will be shallow and primarily be found above treeline for the central-west and southwest Cascades. Treat recently wind loaded slopes with caution with fresh wind slab most likely on NW-SE aspects above treeline.

Recent cornices are very large and have likely been weakened during this most recent storm cycle. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. 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

March was a wet and wild month for weather and avalanches in the Cascades. The last widespread avalanche cycle during this stretch occurred March 28th-29th.

A weak front crossed the Northwest on Saturday morning 4/1, causing light rain mainly along the Cascade west slopes. This was followed by an upper trough that caused some light amounts of snow along the Cascade west slopes at much cooler temperatures on Sunday.

Fair but cool weather has been seen in the Olympics and Cascades Monday and Tuesday. Reports generally indicate strong surface or near surface crust layers and shallow recent snow.

A stalled frontal boundary on Wednesday brought heavy rain and snow to the Mt. Baker area with much much lighter precipitation for the central-west and southwest Cascades. Snow levels were generally between 4500-5500 feet on Wednesday.

Recent Observations

North

NWAC pro-observer Lee Lazzara was at Little Devil Peak in North Cascades on Monday 4/3. Near and above treeline Lee found about 4 inches of recent storm snow over the most recent crust, and wind slabs averaging about 1 foot on N-E aspects below ridges. Snowpack tests indicated triggering of wind slabs to be stubborn. There was evidence of recent large cornice failures. The recent strong rain crust dominated the snowpack below treeline with shallow wet snow conditions during the afternoon. Shallow cold snow was preserved on steep shaded terrain near and above treeline.

Central

On Sunday 4/2, the Alpental pro-patrol only reported minor amounts of new snow on the crust from last week and no avalanches.

South

No recent observations.

Problems

Loose Wet

Loose Wet avalanches are the 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. 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.

Wind Slabs

Wind Slab avalanches are the 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.

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 drifts 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.