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Avalanche Forecast

Archived

Apr 6th, 2014–Apr 7th, 2014

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

Regions

Snoqualmie Pass.

Wet snow avalanche concerns are driving the avalanche danger Monday. Avoid steep and open slopes that have recently received snowfall as the temperature warms and the sun comes out. 

Detailed Forecast

High pressure will build over the PNW on Monday.  Spotty light rain may sneak under the ridge and brush the Olympics and N Cascades Monday morning, but partly to mostly sunny skies are expected in the afternoon.  Freezing levels will pop up on Monday and be accompanied by generally light winds.  In addition, mild temperatures overnight and variable cloud cover will likely prevent the wet near surface snow from a good re-freeze.

The potential for wet snow avalanches should quickly ramp up Monday with high freezing levels and will not be confined only to solar slopes. 

New storm snow instabilities from Saturday night should have settled out, but above 5000 feet, small wet point releases will have the ability to become larger and more dangerous as they entrain new snowfall from Saturday night.  Watch for wet surface snow deeper than a few inches, roller balls in surface snow and small natural wet loose releases that usually precede more major wet loose snow avalanches.  Avoid terrain traps where a small but powerful wet loose avalanche could have unintended consequences. 

Monday is a good day to stay away from large cornices and avoid traveling on slopes below them!  Cornice failures are often seen during the transition to spring weather. Cornices have grown large recently and often break back further from the edge than expected. 

Watch for evidence of wind transported snow above treeline, wind slab my have built on lee aspects of higher terrain Saturday night. 

Snowpack Discussion

A front crossed the Northwest Thursday and Thursday night with moderate winds and varied amounts of new snow. New snow ranged from 8 to 12+ inches in the Mt Baker and Paradise, MRNP areas to 4 inches or less for other west slope Cascade locals. Following the front Thursday, Mt Baker and Alpental patrol reported active results from ski and explosive control work. 

By Saturday, the storm layers had settled significantly with slope testing by ski and explosives in both the Baker and Alpental areas producing limited to no results and only some shallow wet snow conditions below tree line at Alpental by Saturday afternoon.

A quick moving but moist frontal system passed through Saturday afternoon and night, depositing 3-10" of heavy wet snow and with the highest totals near and above 5000 feet.  Strong west winds likely built new areas of wind slab in the above treeline zone Saturday night.  The ranger at Paradise, MRNP reported natural pinwheeling by late Sun morning. The Alpental and Mt. Baker pro-patrol reported widespread wet loose activity on all aspects Sunday afternoon. Storm slab propagation was not extensive and confined to AM control work. 

Cornices have grown large from March and April storms. 

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.