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Avalanche Forecast

Archived

Apr 9th, 2016–Apr 10th, 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 Sunday due to a slight cooling trend, but still remain Moderate. 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

A shift to onshore flow will maintain fair and mild conditions Sunday, but slightly cooler than the previous several days. Winds should remain light Sunday with some night and morning low level clouds possible in the valleys.  Freezing levels and temperatures should remain near 10,000 feet Sunday. Stay aware of the overhead hazard to minimize your exposure. 

Surface crusts should form overnight through the early morning hours followed by gradual melting and weakening. Pay attention to the integrity of surface crusts formed overnight. Loose wet avalanches will be possible on any steeper slope due to warming Sunday. Backcountry travel early in the day is encouraged 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 Sunday. 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 Sunday should be less extensive as during the very warm weather last week which more closely followed a period of heavier snowfall and caused consolidation and some stabilizing. Continue 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, April 3rd, resulting in very warm and dry weather. A spring avalanche cycle occurred in most areas over this stretch, likely peaking a week ago, Thursday and Friday. After a stormy March, the snowpack has undergone significant settlement and multiple melt-freeze cycles over the last two weeks.

The last precipitation occurred early Monday morning with showers Tuesday, depositing storm snow from 2-6 inches, now indistinguishable following several melt freeze cycles during the very warm weather. 

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 unusually 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.