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Avalanche Forecast

Archived

Mar 30th, 2014–Mar 31st, 2014

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

Olympics.

A mix of winter and spring conditions is starting to be seen in the Cascades. You will need to watch for a variety of concerns on Monday.  

Detailed Forecast

A weak vertically aligned low pressure system should drop south over the northeast Pacific Ocean and Northwest coastal waters Sunday night and Monday. This should cause decreasing winds and partly sunny weather in the Olympics on Monday.

The mix of winter and spring snow conditions should continue on Monday. The main concern should begin to shift to wet loose avalanches on Monday. This should be likely on solar slopes in all 3 elevations bands on Monday and will be possible on non-solar slopes. 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.

Watch for areas of recent wind slab on lee slopes. This is likely on shaded north to east slopes near and above treeline. Watch for signs of cracking or firmer wind transported snow and approach open lee slopes with caution.

Recent storm slab may need another day to stabilize on Monday. This is possible on sheltered slopes where there was recent heavy snowfall or graupel which may have formed temporary weaker storm layers. This shorter lived concern will be mainly found on Monday above treeline due to cooler temperatures there.

Remember to watch for cornices if you venture onto ridges on Monday and avoid slopes below cornices. Cornice failures are normally seen during the transition to spring weather.

Snowpack Discussion

The weather pattern got active again over the Northwest starting last Tuesday. There has been about 2 feet of snowfall at Hurricane in the 5 days ending today. Less snow has been seen at lower elevations.

Avalanche conditions also got active this week. We are now seeing a mix of winter snow conditions mainly on shaded slopes at higher elevations and spring snow conditions on solar slopes and at lower elevations..

A frontal system passing through on Friday brought moderate south winds and wet snowfall at Hurricane Ridge, with rain likely not far below in elevation. NWAC observer Katy Reid at Hurricane on Friday reported local wind slab along along lee ridges with pit tests giving stubborn but clean shears. She also found some storm snow instabilities giving clean results in hand tests at about 15 cm or 6" below the surface.

Hand pit results at Hurricane Ridge on Friday by NWAC observer Katy Reid.

Natural wind slab avalanches likely from Saturday were found at Hurricane by Katy on Sunday with several releases up to size 2 mainly 6-12 inches but stepping up to 2.5 feet on a north slope. Tests indicated a clean interface at about 20 cm in the storm snow.

Natural wind slab avalanches found at Hurricane on Sunday 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.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.