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Avalanche Forecast

Archived

Mar 22nd, 2016–Mar 23rd, 2016

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

Regions

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Spring is springing! Watch for rapid changes especially if the sun comes out. Continue to evaluate snow, terrain and cornices carefully on Wednesday.

Detailed Forecast

A bit of a break in the weather should be seen Tuesday night and Wednesday morning. Southwest flow should begin to carry another front to the Northwest beginning in the Olympics and northwest Cascades Wednesday afternoon and to the rest of the Cascades Wednesday night. Significant new snow layers are generally not expected in the Cascades through most of the daylight hours on Wednesday. Remember that you may need to adjust your plans if the next front arrives with wind and rain or snow sooner than expected.

Continued loose wet snow conditions can't be ruled out on Wednesday especially if there are sun or solar effects. Surface crusts in the morning  don't mean that loose wet snow conditions won't develop by the afternoon. This is mostly likely on solar slopes but can't be ruled out on other aspects. Watch for wet snow deeper than a few inches and pinwheels or natural releases.

Recently formed cornices have grown large and with another release reported at Mt Hood on Tuesday. Avoid areas on ridges or summits where a cornice may be present and avoid slopes below cornices. Cornice releases can be unpredictable during the spring.

Small areas of previous wind slab may remain present on lee slopes. This should be mainly northwest to southeast aspects near ridges and summits. Firm wind transported snow and snowpack cracking can be good signs of wind slab layers.

Although not listed as an avalanche problem, glide avalanches can release unexpectedly so avoid areas below steep unsupported slopes or rock faces. See the recent observations above for a good example in the Mt Baker backcountry.

Snowpack Discussion

Weather and Snowpack

About 2-4 feet of snowfall accumulated along the west slopes March 9-15th.

A combination of sun, mild temperatures and then some rain was seen for several days ending about Sunday 3/20. This weather caused about 10-20 inches of consolidation of the recent snow along the west slopes. Surface snow conditions became highly variable, ranging from cold snow or wind buffed surfaces on non-solar slopes to morning crusts and wet snow on solar slopes.

Older winter avalanche problems of wind and storm slab along the west slopes will have mostly settled and stabilized during the mild weather.

Recent storms did build large cornices along ridges in many areas.

A low pressure system crossed the Northwest on Monday and Tuesday. NWAC stations along the west slopes had about 0-7 inches of new snowfall ending on Tuesday morning with the most at Paradise.

The mid and lower snowpack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

The Alpental pro-patrol reported on Tuesday afternoon 3/22 that sun breaks were giving widespread, point release, small loose wet avalanches with 1-2 feet of debris.

NWAC pro-observer Dallas Glass was on Skyline Ridge at Stevens Pass on Tuesday 3/22 and found 6 inches of new snow at 5000 feet. Wind had formed small isolated wind slab which was not reactive with no releases. Ski cuts on specific steep test slopes were giving loose wet avalanches which were running fast and good distances but staying within the cut and not propagating.

The Mt Baker ski area reported small, natural loose wet avalanches releasing from steep rocks or walls on Monday 3/21.

NWAC pro-observer Lee Lazzara was out near the Mt Baker ski area on Sunday 3/20 and found the top 30 cm of snow moist to wet and no significant layers in the top 1 m of snow. He saw debris from recent small loose wet avalanche and glide avalanches and big hanging cornices.

A report via the NWAC observations page for the Alpental Valley for Sunday 3/20 indicated a wet snowpack and that a large loose wet avalanche had run off Chair Peak.

The Mt. Baker pro-patrol reported a glide avalanche to the ground (5-6 feet deep!) on a steep rock face around 3500 feet in the below treeline band off of Shuskan Arm on Tuesday 3/15.

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.

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.

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.