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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

Olympics.

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.  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

About 4-6 inches of new snow accumulated in the Hurricane Ridge area last week.  A strong melt-freeze surface crust on most exposed slopes as of early Saturday morning was reported as a breakable crust by NPS rangers Sunday morning.  A quick moving front Saturday afternoon and night brought a wet 1-2" of snow to Hurricane Ridge with moderate south winds. Partial clearing was seen by Sunday afternoon with temperatures warming into the low 40s. 

NWAC observer Katy Reid, reported Friday that all slopes had a melt-freeze crust with shaded terrain, maintaining 3-4 inches of soft and dryer recent snow being well bonded.  Heavier, moist to wet shallow surface snow was found on solar aspects with some shallow, loose wet slides, releasing on steeper exposed terrain by Friday afternoon.  Wind exposed terrain near and above treeline had been scoured of recent snow to firmer old surfaces. There were also some recent cornice growth noted as well as a few isolated, but stubborn wind pockets on lee slopes in higher terrain. 

 

Natural loose wet avalanche on 35 degree SW facing slope below tree line at Hurricane on Friday, April 4th. By NWAC observer Katy Reid.

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.