Avalanche Forecast
Regions: Olympics.
Detailed Forecast
A change and some uncertainty is in store on Thursday.
A front will begin to reach the Olympics and north Cascades on Thursday afternoon. This should cause increasing southwest winds, increasing rain or snow and lowering snow levels. Snow levels Thursday afternoon should still be high enough to restrict snow to the alpine but up to several inches may be seen there by the end of the daylight hours. Therefore attention in the Olympics and north Cascades will shift to potential new wind and storm slab of several inches in the alpine starting Thursday afternoon. But the cooling and change in most areas from rain to snow should also favor shallow stable snow in many calm areas of the alpine. Rain near treeline or below treeline through Thursday afternoon should not greatly change conditions in those areas.
The uncertainty is due to timing of the storm. If snow arrives sooner or later and snow levels are higher or lower than expected then the expected snow and avalanche conditions would change as well.
The storm will move over the Northwest on Thursday night. This will cause further increasing winds and more snow at further lowering snow levels. The avalanche danger should further increase in the Olympics on Thursday night.
Snowpack Discussion
The weather since mid December in the Northwest and at Hurricane Ridge has been characterized by minor wet snow and rain and periods of mild and routinely above freezing temperatures including at Hurricane Ridge. Partly or mostly sunny weather and warm temperatures will also be seen at Hurricane on Wednesday which should not significantly change the snow conditions.
Snow reports from a NWAC observer on Saturday at Hurricane on a north slope found a strong surface crust with other alternating layers of crusts and rounded grains within the snowpack. No avalanche activity or instability was noted and snow pit test gave no results. Snow on solar aspects and below treeline is shallow or non-existent.
The following photo is of Klahane Ridge showing the shallow snowpack from 22 December by NWAC Observer Katy Reid.
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Avalanche Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1