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Avalanche Forecast

Archived

Apr 8th, 2016–Apr 9th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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The avalanche danger should lower slightly on Saturday due to slight cooling but still land firmly in the Moderate range. Larger avalanches caused by glide releases or cornice fall are possible in isolated areas. Get off steep slopes early in the day and be aware of the overhead hazard to minimize your exposure. 

Detailed Forecast

Another sunny day with warm temperatures and generally light winds are expected Saturday along the east slopes. Freezing levels and temperatures should lower a notch on Saturday. As a result, the avalanche danger should lower slightly Saturday but still land firmly in the Moderate range. Get off steep slopes early in the day and be aware of the overhead hazard to minimize your exposure. 

Loose wet avalanches will be possible on any steeper slope due to warming Saturday. Pay attention to the integrity of surface crusts formed overnight. Backcountry travel early in the day is recommended since conditions can change rapidly due to daytime warming. Watch for wet snow deeper than your boot tops especially on steep solar slopes during the late morning to afternoon hours.

The potential for cornice releases will continue on Saturday. Cornice releases can be unpredictable during the spring so avoid areas below cornices and remember that cornices can break much further back than expected along ridges.

Although not listed as an avalanche problem, large, powerful glide avalanches can release unexpectedly so avoid areas below steep unsupported slopes or rock faces.

Avalanche activity on Saturday is not expected to be as extensive as during the warm weather last week which more closely followed a period of heavier snowfall and caused consolidation and some stabilizing. Hence the Moderate avalanche rating in all areas versus the Considerable rating forecast last week. You will need to evaluate avalanche conditions on specific terrain features and change your plans if snow conditions are more dangerous than expected.

Snowpack Discussion

Weather and Snowpack

A large upper ridge dominated the weather last week through early Sunday, resulting in very warm and dry weather. A spring avalanche cycle occurred in most areas over this stretch, likely peaking Thursday or Friday during the warmest temperatures and lightest winds. After a stormy March, the snowpack has undergone significant settlement and multiple melt-freeze cycles over the last week.

A front moved across the Cascades early Monday morning, resulting in a period of mostly light precipitation, cooling and moderate westerly crest level winds. Precipitation transitioned from rain to snow as cooling occurred, forming a generally good bond to the old melt freeze crust. Most east slope areas received storm snow amounts ranging from 2-6 inches as of Tuesday.

Another upper ridge is currently over the Northwest causing sunny weather and warm temperatures. Another upper ridge is currently over the Northwest causing sunny weather and warm temperatures. High temperatures at many NWAC stations throughout the Cascades pushed into 50s, 60s on Thursday with even a few 70s recorded Friday afternoon!  

Frequent March storms have built large cornices along many ridges.

No persistent weak layers formed earlier this winter are layers of concern as we transition to a spring snowpack along the east slopes. 

Recent Observations

Professional observations received last week focused on the spring avalanche cycle that occurred during the warm stretch from late March through the first weekend in April.   

No observations have been received this week along the east slopes of the Cascades. 

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.