Avalanche Forecast
Regions: Olympics.
Light snow and moderate winds will create heightened avalanche danger on wind loaded slopes near and above treeline Thursday. Use visual clues such as fresh cornices, wind drifted pillows and cracks in the snow all indicating that you could trigger a Wind Slab avalanche. Shallow Storm Slabs may build over a newly forming crust. Watch for and avoid deeper drifted snow on steep slopes. Be alert to overhead hazards such as cornices by giving them a wide margin of safety.
Detailed Forecast
The avalanche danger will shift to new Wind and Storm Slabs formed with and after a cold frontal passage overnight Wednesday. Periods of moderate winds with light to moderate snowfall at cooling temperatures will make triggered slab avalanches possible by Thursday, especially on steep slopes receiving wind transported snow. Use visual clues such as fresh cornices, wind drifted pillows and cracks in the snow all indicating that you could trigger a Wind Slab avalanche.Â
The cooling temperatures will allow for old wet snow to consolidate and refreeze, limiting any Wet Snow avalanches.Â
Watch for other spring hazards such as recent cornices along ridges, open glide cracks an opening creeks.
Snowpack Discussion
New wind and snow is arriving at cooling temperatures late Wednesday. This is allowing old wet snow to begin re-freezing while building new shallow wind and storm slab layers.
Warm and dry conditions were seen on Monday, following a strong storm over the weekend that brought rain Saturday to high elevations followed by cooling and new storm snow of around a foot by Sunday afternoon. The weekend snow built fresh Wind Slabs on a variety of aspects, especially below ridges and cornices along exposed ridges.Â
Older weak snow had been observed on N-E aspects near and above treeline above a crust prior to this weekend's storm about 1-1.5 ft below the surface. This interface is likely no longer an issue due to recent rain and warm temperatures.Â
There are no other significant layers of concern in the snowpack at this time.
Observations
Park rangers reported about 1 ft of new snow as of Sunday morning.
On Friday 4/6, NWAC professional observer Matt Schonwald found the facets above a crust on NE aspects between 5200-5400 ft healing. While this interface may have come into play with Wet Slabs last Saturday, the Persistent Slab problem has ended. Matt also found glide cracks in isolated areas. The snowpack on solar aspects is becoming patchy, especially below treeline.Â
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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1