Avalanche Forecast
Regions: Cascades - North West.
Large, but isolated avalanches are releasing to ground in the Mt Baker area on steep, rock faces. These avalanches are difficult to predict and best managed by avoiding terrain below glide cracks. Watch for wind stiffened slabs on some isolated steep shaded slopes at higher elevations exposed to recent strong south winds. Watch for shallow wet surface snow conditions on some steep sun exposed slopes, especially below rocks or cliffs and above terrain traps.
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.Â
At the higher terrain Sunday, temperatures reached the mid-50's with similar conditions expected Monday.
Large, but isolated avalanches are releasing to ground in the Mt Baker area on steep, rock faces. These avalanches are difficult to predict and best managed by avoiding terrain below glide cracks.
Recent wind slabs should continue to settle but pay attention for those specific features where snow may have been available for transport to steep shaded slopes.
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. Â
The nice riding and skiing conditions found Sunday should remain on Monday as little change in the snowpack structure is expected.Â
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 3-5Â feet, with the most over the volcanic peaks.
Strong crest level southerly wind Friday night to midday Saturday may have built some wind slab layers in isolated terrain. However, moist surface snow on windward slopes likely limited available snow for transport. Watch for isolated recent wind slabs on shaded slopes in the north WA Cascades where the winds were strongest.
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. Â
The snowpack is well consolidated and strong with settled old storm snow of about 1.5-2.5Â feet over the strong Thanksgiving rain crust.Â
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.Â
Observations
Don't forget to check the numerous recent high quality observations posted to NWAC.
North
Updated: Pro patrol at Mt Baker Ski area reported two climax/glide avalanches off rocks. The slides were in typical locations on an east and a south face, both were about 30 feet across and 3 feet deep, with debris piles 4-5 feet deep.Â
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.Â
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.
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.
Avalanche Problems
Glide Cracks
A release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often preceded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
Predicting the release of Glide avalanches is very challenging. Because Glide avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide avalanches.
This Glide avalanche broke to the ground on a smooth, grassy slope. From all the mud on the bed surface, water pooling at the base of the snowpack likely caused the failure.
Glide avalanches occur when water lubricates the interface between the snowpack and the ground. These avalanches are difficult to predict and best managed by avoiding terrain below glide cracks.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Unlikely
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: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Unlikely
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: South East, South, South West.
Elevations: All elevations.
Likelihood: Unlikely
Expected Size: 1 - 1