Avalanche Forecast
Regions: Olympics.
Overall the avalanche danger will be less on Wednesday than the past few days. But small areas of new wind slab might be possible depending on the local strength of the east to southeast winds.
Detailed Forecast
A low pressure and frontal system should pass by to the south across Oregon and north California on Wednesday. It looks like this will system will cause light to moderate southeast winds in the Olympics and Cascades and mostly light snow over Mt Hood and the south Cascades on Wednesday.
Overall the avalanche danger will be less on Wednesday than the past few days. But small areas of new wind slab might be possible depending on the strength of the east to southeast winds.
New wind slab should not be extensive as east to southeast winds are not expected to be strong on Wednesday. Since older wind slab is still possible on mainly north to southeast aspects and new local wind slab is possible on northwest to west aspects, wind slab will be indicated on all aspects. Watch for firmer wind transported snow which would be be more extensive if winds are stronger than expected.
Storm slabs from the recent storm cycle will further settle on Tuesday.
There is a confirmed persistent weak layer from about December 8th in the Washington Cascades. This type of layer is less common in the Olympics and it won't be listed here as an avalanche problem. We don't have any snowpack observations identifying a persistent weak layer in the Olympics. But ratchet back your plans if you experience collapsing or whoomping. Some time and snowpack tests from many areas will be needed to determine to what extent this layer is a regional problem.
Loose dry avalanches will not be listed as an avalanche problem on Tuesday. But in steep terrain lacking a slab structure continue to watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences.Â
With deep unconsolidated snow in many wind protected areas there remains a risk for tree well and snow immersion suffocation at this time. Ride or ski with a partner and keep them in sight at all times!
Even though the lower part of the below treeline band is filling in, watch for early season travel hazards such as barely covered rocks and open creeks.
The regional avalanche danger is expected to further slightly decrease on Thursday.
Snowpack Discussion
Weather and Snowpack
Cold and fair weather was seen early last week.
The latest storm cycle began about December 8th starting with a couple day warming trend as southwest flow eroded an Arctic air mass over the Northwest. The warming trend leveled off with temperatures staying well below freezing December 10th and 11th and snowfall tapered off on December 12th. It looks like Hurricane had about 3 feet of snowfall for the 4 days ending Monday morning. Â
Recent Observations
A regional storm and avalanche cycle was seen about Thursday to Sunday with some avalanches releasing on the December 8th layer.
South winds were seen at Hurricane during the storm cycle. These winds should have redistributed snow to N-SE aspects.
The NPS ranger at Hurricane Ridge indicated widespread natural slides had reached the road in many places by Sunday morning, likely releasing overnight during moderate to heavy snowfall.
There is a report via the NWAC Observations tab from Sunday of a triggered slab avalanche on a steep east slope apparently above Lake Angeles.
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: All aspects.
Elevations: Alpine, Treeline.
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: All elevations.
Likelihood: Unlikely
Expected Size: 1 - 1