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Avalanche Forecast

Archived

Apr 12th, 2018–Apr 13th, 2018

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

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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.

Problems

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.

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.