Avalanche Forecast
Regions: Olympics.
A continued mix of winter like and spring conditions should be seen Saturday. The timing and strength of the incoming front on Saturday will be important for avalanche concerns on Saturday.
Detailed Forecast
A front with increasing clouds and moisture will move to the Northwest Saturday afternoon and night. This is expected to cause increasing winds and increasing rain and snow with slightly rising snow levels first in the Olympics Saturday early afternoon and in the Cascades Saturday late afternoon. The timing and strength of this system will be important for avalanche concerns on Saturday. If the system arrives sooner than expected then new wind slab and storm slab will begin to form sooner in the day. If the system arrives later or weaker then significant new wind slab and storm slab may not form before the end of the daylight hours.
After solar effects, avalanches and consolidation today and overnight cooling tonight the avalanche danger will lower Saturday morning.
Clouds should increase first over the Olympics on Saturday and cut down on solar effects compared to Friday. So wet loose avalanche activity should be less on Saturday. But wet loose avalanches will be listed as possible on Saturday. This should be mainly on solar slopes in all the elevation bands. Watch for natural avalanches, pinwheels and surface wet snow deeper than a few inches on any solar slope.
The formation of new wind slab as mentioned above depends on the timing and strength of the incoming system. The formation of new wind slab on lee slopes is expected to be likely in the Olympics Saturday afternoon. This should be mainly north to southeast slopes near and above treeline. Watch for signs of cracking or firmer new wind transported snow and approach open lee slopes with caution.
The formation of new storm slab as mentioned above also depends on the timing and strength of the incoming system. The formation of new storm slab is also expected to be likely in the Olympics Saturday afternoon. This should be mainly on sheltered slopes near and above treeline in areas that receive more than a few inches of snow by the end of the day. Storm slab forms where bonds are poor to previous snow or where wind or where temperature changes create temporary weak storm layers.
Snowpack Discussion
March ended with a return to winter. A storm cycle peaked last weekend and delivered about 2 feet of snow to the NWAC station at Hurricane. Natural wind slab avalanches were found at Hurricane by NWAC observer Katy Reid on Sunday with several releases up to size 2, mainly 6-12 inches, but with one slab stepping down 2.5 ft on a north slope. Tests indicated a clean interface at about 20 cm in the storm snow.
Natural wind slab avalanches found at Hurricane on Sunday 30 March by NWAC observer Katy Reid.
A fair weather period with less avalanche activity was seen mid-week.
A front crossed the Northwest on Thursday causing moderately increasing winds, varied amounts of new snow and slightly lower snow levels. Hurricane Ridge had about 4 inches according to the ranger with more seen in the Cascades.
Significant storm slab and wet loose avalanches were seen in the Cascades on Friday. Due to less snow, less but some activity was probable at Hurricane.
Avalanche Problems
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: South East, South, South West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
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.
Elevations: Alpine, Treeline.
Likelihood: Likely
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: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1