Avalanche Forecast

Archived

Apr 28th, 2018–Apr 29th, 2018

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

Olympics.

Cooling and showers have allowed shallow new snow to accumulate above treeline, where wind deposited snow will create a localized increase in avalanche danger, mainly near ridges at higher elevations. The snowpack has consolidated and stabilized in lower elevations.

Detailed Forecast

Cool and showery weather will continue Sunday. Some shallow new snow is likely to accumulate above treeline Sunday and while expected winds should be light, any locally stronger winds may drift new snow and build some shallow wind slabs, mainly near ridges on lee slopes.

A high degree of uncertainty exists in the expected new snow amounts, so watch for heavier showers that may quickly build new snow layers and be prepared to change travel plans and remain on lower angled slopes, avoiding exposure to steeper terrain above.

At lower elevations watch for generally shallow wet snow conditions that may make small triggered Loose Wet avalanches possible on some steep slopes, generally over 35 degrees.

Snowpack Discussion

The snowpack is now well drained and has transitioned to spring-like conditions following last weeks very warm temperatures. The cooling and showery weather since late Friday has allowed for consolidation and re-freezing surface snow, limiting the avalanche potential in most areas.

Some shallow wet surface snow conditions continue at lower elevations that lack a refreezing crust, especially during the warmest part of the day.

Strong high pressure brought very warm temperatures to the Olympics from Monday through Friday, with daytime temperatures at Hurricane Ridge above 60 F Tuesday-Friday.

Aided by the recent warm weather, the Olympic snowpack has consolidated 2 ft since it's season maximum near and above treeline on 4/17.

Observations

A National Park ranger at Hurricane reported a few inches of new wet snow as of Saturday morning, over a supportive and consolidated snowpack.

A National Park ranger flew over the Blue Glacier on Mt. Olympus on 4/25 and observed small Loose Wet avalanches on sun-cooked west-facing slopes with no other avalanches observed.

NWAC pro-observer Matt Schonwald visited the Hurricane Ridge area 4/20 and reports no significant layers of concern within the snowpack and generally small cornices.

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.

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.