Avalanche Forecast
Regions: Cascades - North East.
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. Many areas have a very shallow snowpack below treeline making travel difficult.
Detailed Forecast
More of the same weather is expected for Sunday, mostly sunny and warm with light winds.Â
In areas away from the lower elevation passes, many NWAC weather stations have seen temperatures reaching the low 50's Saturday and similar conditions are expected Sunday.
Surface melt-freeze crusts should form overnight on solar exposed slopes and gradually melt through the day. Loose wet avalanches should be less likely Sunday and mainly confined to steep sun exposed slopes below rocks or trees absorbing abundant radiation. Watch for terrain such as this if the surface snow is melting more than a few inches.Â
Older wind slabs should have mostly settled and stabilized and will be removed from the avalanche problem list, but continue to look out for areas of wind stiffened snow deposited mainly near ridges on steep shaded terrain.
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 a full week. Sunshine and very mild temperatures have been the story at mid and higher elevations with cool to cold temperatures at lower elevations. This weather has allowed for overall strengthening and consolidation of an already strong snowpack.
Some small loose wet slides have occurred on mainly steep sun exposed slopes through the week, but have become less frequent over the past few days.
At the beginning of the high pressure earlier this week, some areas experienced strong easterly crest level wind, transporting loose snow and building some wind slab layers mainly near or above treeline. No triggered wind slabs have been reported recently as these layers continue to settle and bond under warm temperatures. Older wind slabs may still persist, 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.Â
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 total snowpack height in these zones varies mostly from 3-5Â feet, with the most in the north zone nearer the crest.
The snowpack is well consolidated and strong with settled old storm snow of about 1-2Â feet bonded well to the strong Thanksgiving rain crust.Â
During this high pressure pattern, surface hoar and or surface facets have been formed, and grown quite large in some areas, especially the typical sun and wind sheltered terrain at lower elevations in the cooler temperatures below the inversion. We will need to watch for these potential weak surface snow conditions as they may have an impact on future avalanche conditions when snowfall returns.Â
Observations
North
A party of NCMG guides, training in the Washington Pass area on Thursday and noted the temperature inversion at the Pass, good bonds to the Thanksgiving crust, some small loose wet activity on solar slopes, with little avalanche concerns below treeline.
Central
On Wednesday a party in the Gallagher/Hawkins area reported nice conditions on shaded terrain up to 6700 feet, with only a few small wet snow avalanches on steep solar aspects.
South
No recent observations.
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, West, North West.
Elevations: Alpine.
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: South East, South, South West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1