Avalanche Forecast
Regions: Olympics.
Dangerous avalanche conditions are expected at Hurricane on Saturday. Careful snowpack evaluation, cautious route finding and conservative decision-making will be essential.
Detailed Forecast
Active weather and avalanches should be seen this weekend!
A front will approach the Northwest Saturday morning and should cross the Cascades Saturday midday. This will cause increasing winds and moderate to heavy rain or snow with warming on Saturday. A change to rain or snow showers should be seen following the front Saturday afternoon and night.
This weather will build generally upside down snow layers of increasing density near the surface and snow may also change to rain in some areas. About 6 inches to a foot of upside down snow should be seen at Hurricane by late Saturday.
New wind slab will also be very likely mainly on lee north to east slopes.
New storm slab due to the warming trend is also very likely on varied aspects where winds are lighter and snow rapidly accumulates to deeper than a few inches.
Avalanches releasing in near surface layers on Saturday may entrain previous snow producing large avalanches.
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Snowpack Discussion
Deep storm snow that fell during mid-late December is well settled, homogeneous and has stabilized so the current avalanche danger focus will be on the upper snowpack.
Fair weather over the New Year caused extensive surface hoar and near surface faceted snow. This was buried by about 6 inches of snowfall at Hurricane about January 3-6th.
The last observation for Hurricane is from NWAC pro-observer Matt Schonwald at week ago and he generally found a right side up, stable snowpack. Older wind slab was limited to 6-12 inch (15-30 cm) pockets near ridges and tests indicated little propagation. Matt observed new surface hoar primarily on the sheltered north-east slopes. But this surface hoar was likely destroyed by mild temperatures and rain Monday or Tuesday. Strong winds and rain up to at least 5500-6000 feet Tuesday likely caused a loose wet avalanche cycle on steeper slopes near and below treeline.
The latest period of snowfall has been from about January 11-15th with about 5 inches of snowfall at Hurricane. A cooling trend was seen at the tail end Thursday.
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, Treeline.
Likelihood: Likely
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: All elevations.
Likelihood: Likely
Expected Size: 1 - 1