Avalanche Forecast
Regions: Olympics.
Human triggered avalanches will become more likely as denser storm slab continues to build over less dense older snow near and above treeline as snowfall intensities increase during the day Friday. Watch for building wind slab on a variety of aspects near and above treeline where either older less dense or newer denser snow has been transported onto lee slopes. As rainfall increases and moves to higher elevations, watch for saturated snow and avoid consequential terrain features. Watch for changing conditions, travel conservatively and rein in your plans as conditions deteriorate throughout the day.
Detailed Forecast
A second storm (Friday) on the heels of the first (Thursday), will bring significantly more precipitation and further warming than the initial system. The storm track that will bring moderate NE-SE winds shifting to SW during the day, along with further warming, increasing precipitation intensities, and snow lines rising above ridge crest level (at Hurricane) late in the day. Sharp cooling and drying should arrive during the evening hours.
Wind and storm slabs will be increasing in size and likelihood of human triggering as slabs of increasing thickness build over the lower density, weaker, older snow prior to Thursday and become increasingly touchy by later in the day. Especially watch for building wind slab on a variety of aspects as winds directions shift during the storm. Wind and storm slab issues will be confined to increasingly high elevations as the rain/snow line works it's way to higher elevations during the afternoon hours.
On Friday morning, loose wet avalanches are mostly likely encountered below treeline on steeper slopes due to warming and light to moderate rain. By afternoon, loose wet avalanches will be found further up in the near treeline band. At higher elevations which have received more snowfall, the loose wet slides will be larger and and increasingly consequential. In general, when snow is becoming saturated, avoid complex terrain as loose wet avalanches will be much more dangerous.
Watch for changing conditions, travel conservatively and rein in your plans if conditions deteriorate faster than expected. See the mountain weather tab for weather forecast details.Â
Also despite all the new snow, early season hazards still exist at some lower elevation locales and especially around creek beds that are not filled in.
Snowpack Discussion
At Hurricane Ridge, the frontal system arriving Thursday brought light snow with temperatures just below freezing, with light to occasionally moderate SW winds.
Light snow also accumulated during a series of very weak weather disturbances that traversed the area in about the past week.Â
The previous significant storm and snowfall was was 12/19-12/20.
Observations
The rangers reports that on Wednesday 12/27, the long narrow Tunnel path on a northeast slope above the roadway produced a loose wet avalanche that was small by the time it reached the road.
Also from the rangers, on Sunday 12/24 a skier triggered a loose dry avalanche on a north facing slope at 5200 ft on a run called Lost Bowl.Â
NWAC pro observer Matt Schonwald was also at Hurricane Ridge on Sunday 12/24 and reported evidence of north to east winds but no wind slab or significant layers in the upper snowpack. The snowpack structure was generally right-side with good bonds to the Thanksgiving crust.
Avalanche Problems
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, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
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
Loose Wet
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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1