Avalanche Forecast

Archived

Apr 21st, 2018–Apr 22nd, 2018

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

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A significant warm-up in the Mt Baker area Sunday will affect the snow creating wet avalanche conditions. New rollerballs, fresh fan-shaped avalanche debris, and wet surface snow deeper than your ankle all indicate that you may trigger a loose wet avalanche on similar slopes. Use visual clues such as fresh cornice, drifted snow, and uneven snow surfaces to identify and avoid lingering winds slabs at higher elevations.

Detailed Forecast

Wet avalanche conditions will quickly develop Sunday as warm air temperatures and sunny skies affect the snowpack. When you see new rollerballs, observe fresh fan-shaped debris, or experience wet surface snow deeper than your ankle, you may be able to trigger loose wet avalanches on similar slopes. Do not underestimate these loose wet avalanches. Observations from this week have shown that many small slides have gouged into older snow layers, grown large, and traveled farther down slope than normal.

Wind slabs formed on lee slopes near and above treeline in the Baker area Saturday. You are most likely to trigger a lingering wind slab below cornices, near convex rollovers, or on unsupported slopes. Use visual clues such as fresh cornices, drifted snow, and uneven snow surfaces to identify and avoid these wind loaded features.

Many cornices have grown large over the winter. This time of year, warm sunny weather causes them to droop and eventually fail. This warm-up may be significant enough to cause this to occur. Do not linger in areas where cornices are above you. Choose travel routes and techniques that limit your exposure to these potential ticking time bombs.

We have received reports of isolated very large wet slab and glide avalanches from most areas over the past week. Many of these avalanches appear to have been triggered by cornice falls or loose wet avalanches. During significant warm-ups such as this, minimize your time in very large avalanche paths by choosing routes and techniques that reduce your exposure

Other springtime hazards exist in the mountains. Creeks have begun to open, running high and fast with snowmelt. Use caution and choose your creek crossings carefully if you are traveling near or over large creeks.

Snowpack Discussion

Six to eight inches (15-20cm) of snow fell in the Mt Baker area Saturday with more snow falling at higher elevations. Moderate winds during the storm transported the new snow forming new wind slabs on lee slopes. Near and below treeline, this new snow fell on a melt-freeze crust. The thickness and strength of the curst depends on aspect and elevation. On shaded slopes above treeline, this new snow fell on strong settled snow.

The upper and mid snowpack is quite variable depending on aspect and elevations. In general, the upper snowpack consists of frozen melt-freeze crusts, weak large wet grains, and strong rounded grains. The 4/1 melt-freeze crust which may be the culprit in some of these recent very large wet slab avalanches is generally found 4-6 feet (120-200cm) below the snow surface.

Very large slab and glide avalanches have been reported over the last several days. Mt Baker, Stevens Pass, Alpental Valley, Chinook Pass, and the Mt Rainier area have all reported very large deep avalanches. They are a reminder that very large triggers, such as cornice falls or other avalanches, may trigger older deep layers that have become wet with recent rain and warm temperatures.

Observations

Baker

On Thursday NWAC professional observer Lee Lazzara traveled near Heliotrope Ridge. Lee found lingering wind slabs 12-16 inches (30-40cm) near and above treeline. Below 5000 feet, all aspects had formed moist to wet snow on the surface. Lee reported one very large avalanche in the Sisters Range SW of Mt Baker.

Problems

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.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.