Avalanche Forecast
Issued: Dec 10th, 2017 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet.
NWAC,
Northwest Avalanche Center
The snowpack is strong and well consolidated after a week of mild dry weather. Watch for wet surface snow conditions on some steep sun exposed slopes, especially below rocks or cliffs and above terrain traps where even small slides could be dangerous.
Summary
Detailed Forecast
More of the same conditions are expected Monday. Mostly sunny and warm with light winds at higher elevations and cold and cloudy conditions in the lower passes and some low elevations.
At the higher terrain Sunday, temperatures reached the mid-50's to 60F at Paradise with similar conditions expected Monday.
Surface melt-freeze crusts are forming overnight on some solar exposed slopes and softening through the day. Loose wet avalanches are unlikely, but might be encountered in isolated steep solar exposed slopes below rocks or trees absorbing more radiation.
The nice riding and skiing conditions found Sunday should remain on Monday as little change in the snowpack structure is expected.
Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.
Snowpack Discussion
High pressure has now been over the region for over a full week. Sunshine and very mild temperatures have been the story with cooler temperatures at lower elevations and in the passes. This weather has allowed for overall strengthening and consolidation of an already strong snowpack.
No triggered avalanches have been reported since Tuesday.
Some small loose wet slides have occurred on mainly steep sun exposed slopes through the week, but have become much less frequent over the past several days.
The total snowpack height in these zones varies mostly from 3-5 feet, with the most over the volcanic peaks.
Older wind slabs have settled and bonded but might be found in isolated terrain features, mainly near and above treeline on mostly westerly to northerly facing terrain, especially below ridges. These slabs should be more reluctant to trigger as they continue to bond and strengthen.
The surface snow consists mainly of surface melt freeze crusts forming overnight on solar aspects, On shaded aspects, settled storm snow is still providing some nice skiing and riding conditions.
The snowpack is well consolidated and strong with settled old storm snow of about 1.5-2.5 feet over the strong Thanksgiving rain crust.
During this high pressure pattern, surface hoar and or surface facets have been developed in some areas and not in others. At some lower elevations under the strong inversion, very large surface hoar has been seen. Less surface hoar growth has been reported in typical start zone terrain however. These potential weak surface snow conditions will be important when the snowfall returns, as they may have an impact on future avalanche conditions.
Observations
North
NWAC observer, Lee Lazzara travelled extensively Sunday, December 10th in the Swamp Creek / Winchester area from 3000-6100 feet. While the temperatures were quite warm and melting evident, surprisingly little current or previous loose wet avalanche activity was noted, mainly tree bombs. No avalanche activity was noted with variable but good ski quality in well settled storm snow, well bonded to the T-Day crust. Very little to no surface hoar or near surface facets were seen, other than in non-avalanche terrain near valley bottoms and creeks.
Mt Baker ski area snow safety on Saturday reported no avalanche activity and relates a strong and settled snowpack. Loose wet avalanche activity has diminished over the past few days.
Central
Numerous recent reports over the past few days indicate creamy settled storm snow still providing nice skiing and riding conditions on sun sheltered aspects.
Thursday and Friday the Alpental pro-patrol saw minor roller balls and point releases on steep solar slopes and cold snow on non-solar slopes. Good bonds were seen on the Thanksgiving crust down 67 inches near the mountain top.
A report via the NWAC Observations for Stevens on Tuesday indicated a favorable snow density profile (gradually increasing with depth) on non-solar slopes, moderate to hard tests in recent snow and a good bond to the T Day crust.
South
Friday the Crystal pro-patrol reported only a few roller balls on steep solar slopes that were not entraining snow, with some previously scoured areas getting melted to the ground.
NWAC staff avalanche training at Mt Rainier Thursday reported an overall strong snowpack on westerly aspects of Mazama Ridge near Paradise. At 5400 feet the height of snow was about 4 feet with the Thanksgiving crust well bonded about 2 feet below the surface. Settled storm snow with few remaining storm layers provided nice conditions on non-solar aspects. Previous wind effected snow was visually evident on exposed slopes near and above treeline but not visited.
The Crystal pro-patrol on Wednesday reported east winds has stripped the snow along windward ridges, but little snow remained for significant transport. Settled powder remained on northerly aspects not wind buffed.
Problems
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: South East, South, South West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 11th, 2017 10:00AM
