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Archived

Avalanche Forecast

Mar 28th, 2014–Mar 29th, 2014
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

Saturday should be a tricky day to manage avalanche concerns. Recent and new wind and storm slab instabilities should prevail at higher elevations with wet loose concerns at lower elevations.  Periods of heavy showers and daytime warming effects can quickly change the likelihood of avalanches, choose conservatively and pay attention to changes throughout the day.    

Detailed Forecast

A shortwave trough passing through the Olympics mid-morning should bring about a period of more organized showers followed by more scattered but occasionally heavy showers in the late afternoon and even the chance of a thunderstorm.  Snow levels should gradually lower Friday night into Saturday.  Moderate southwest winds should continue to transport recent snowfall to lee slopes near and above treeline Saturday.  

More wintry avalanche concerns are likely at higher elevations Saturday with more spring-time concerns at lower elevations. Despite the cooling trend, new or recent storm slab formed Friday or Saturday may still be sensitive near and above treeline. Unconsolidated new snow found in the morning may become a slab with day-time warming...even on cool spring days. Be aware of intense precipitation rates on Saturday during heavier showers that could lead to new storm snow instabilities or unstable graupel layers. Wind or storm slab on higher lee slopes near and above treeline have not had enough time to settle out. Watch for signs of cracking or firmer wind transported snow and approach open lee slopes with caution.   

Despite mostly cloudy skies Saturday, wet loose concerns are still possible at lower elevations especially on steeper slopes in the afternoon. Watch for wet surface snow deeper than a few inches, roller balls in surface snow and small natural wet loose releases that usually precede more major wet loose snow avalanches.  Even brief sunbreaks could quickly extend the wet loose concern to higher elevation solar aspects.  Avoid terrain traps where a small but powerful wet loose avalanche could have unintended consequences. 

Snowpack Discussion

After a warm day Monday, cooling and a frontal passage Tuesday deposited about 8-12 inches of new snow in the Hurricane Ridge area through Wednesday morning.  Snow showers Wednesday and Thursday added a few inches to these storm totals.  Daytime highs at the Hurricane Ridge weather station still reached above freezing mid-week...likely promoting rapid settlement of storm snow instabilities near and below treeline. 

A frontal system passing through on Friday brought moderate south winds and wet snowfall at Hurricane Ridge, with rain likely not far below in elevation.  Showers and slightly cooler temperatures Friday night should bring an additional a few inches of snowfall.   NWAC pro observer Katy Reid reported Friday that stubborn wind slab found along lee ridges in the Hurricane Ridge area.  She also found some storm snow instabilities giving clean results with snow pit tests about 15 cm or 6" down below treeline on an east aspect.  

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: 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

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.

Elevations: Below Treeline.

Likelihood: Possible

Expected Size: 1 - 1