Avalanche Forecast

Archived

Apr 4th, 2014–Apr 5th, 2014

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

Olympics.

New winter like layers should be seen mainly near and above treeline on Friday. But spring snow conditions are also possible on solar slopes.

Detailed Forecast

A slow moving weak cold front will cross the Northwest Thursday afternoon and evening. This will cause increasing winds and increasing rain or snow. A weak upper short wave, cooler air mass and mostly light showers should follow across the Northwest on Friday. But only a couple inches of new snow should be seen near and above treeline at Hurricane by Friday morning.

Small shallow new wind slab will be possible on lee slopes. This should be mainly north to southeast slopes near and above treeline. Watch for signs of cracking or firmer wind transported snow and approach open lee slopes with caution.

Shallow small new storm slab should also be possible on more sheltered slopes mainly near and above treeline. This is most possible in areas that receive at least a few inches of snow. Storm slab forms where bonds are poor to previous snow or where wind or where temperature changes create temporary weak storm layers.

Now that it is April we can't rule out possible wet loose snow avalanches. Clouds and cool temperatures should mostly limit this to solar slopes below treeline but it will be listed as a concern for solar slopes in all the elevation bands. Watch for pinwheels and surface wet snow deeper than a few inches on any solar slope.

Remember to watch for cornices if you venture onto ridges and avoid slopes below cornices. Cornice failures are often seen during the transition to spring weather. Cornices have grown large recently and may break back further from the edge than expected.

Snowpack Discussion

March ended with a return to winter. A storm cycle peaked last weekend and delivered about 2 feet of snow to the NWAC station at Hurricane. Natural wind slab avalanches likely from Saturday were found at Hurricane by NWAC observer Katy Reid on Sunday with several releases up to size 2, mainly 6-12 inches, but with one slab stepping down 2.5 ft 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 30 March by NWAC observer Katy Reid.

A fair period with warmer daytime temperatures and cooler night time temperatures was seen most of this week.The overall cool temperatures may be limiting wet loose avalanches. The Park ranger at Hurricane Tuesday morning reported widespread but shallow loose wet slides that released during warming Monday.

Problems

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.

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.