Avalanche Forecast
Regions: Cascades - North West.
Significant precipitation, warming temperatures, and wind will create dangerous avalanche conditions Friday in the Mt Baker backcountry. Expect avalanche problems to grow larger and easier to trigger as the day progresses. Avoid avalanche startzones greater than 35 degrees and limit your exposure to overhead terrain during periods of higher precipitation.
Detailed Forecast
Avalanche danger will increase throughout the day Friday as additional precipitation and warming temperatures impact the Mt Baker area. Expect avalanche problems to grow and become easier to trigger throughout the day. Avoid all slopes greater than 35 degrees Friday as this weather system creates dangerous avalanche conditions.
Moderate to strong winds will form new wind slabs on lee slopes at higher elevations. Use visual clues such as blowing snow, fresh cornices, and snow drifts to identify and avoid steep wind loaded terrain.
Warming air temperatures during the day will create “up-side-down†surface snow conditions where heavier stronger storm snow sits atop lighter weaker storm snow. You will find storm slabs in wind sheltered areas throughout the terrain. Storm slabs are easiest to trigger on convex rollovers, unsupported slopes, and on steeper slopes.
As the day warms and rain begins to fall, storm slab conditions will transition to loose wet snow below treeline. Rain on new snow is an obvious sign unstable snow exists in the terrain. When you see new roller balls, observe fan shaped avalanche debris, or experience rain on snow, limit your exposure to steep overhead terrain where avalanches may initiate.
Other spring-time hazards exist in the mountains. Watch for large overhead cornices, glide cracks and opening creeks.
Snowpack Discussion
Around 8 inches (20cm) of new snow fell in the Mt Baker area Wednesday night into Thursday morning. Observations showed this new snow was well bonded to the most recent (4/11) melt-freeze crust. The new crust was generally weak and unsupportable Thursday. Winds drifted snow Thursday forming soft wind slabs on exposed features.
Daytime warming and thinning clouds quickly affected the snow surface on all aspects. New roller balls and small loose wet avalanches occurred in steep terrain.
The last several days has allowed the upper snowpack to gain strength. Observations show the snowpack is comprised of several melt-freeze crusts, refrozen snow, and strong rounded grains. This has created a strong spring-like snowpack. Avalanches should be limited to the snow above the most recent (4/11) crust layer.
Observations
NWAC professional observer Lee Lazzara traveled in the Baker backcountry Thursday. Lee found 8 inches (20cm) of new snow well bonded to the old snow surface. While Lee did see wind slabs, no wind slab activity was reported. Warming air temperatures and thin clouds resulted in several small (D1) loose wet avalanches in the afternoon.
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: 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: All elevations.
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.
Elevations: Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1