Avalanche Forecast
Regions: Cascades - North West.
A significant buried weak layer is present in the terrain on sun, sheltered slopes above 5000'. This layer will produce avalanches with the additional load of a single skier or rider that could bury, injure or kill. These avalanches can be remotely triggered, propagate around and beyond the natural confines in the terrain, and run on slopes lower in angle than where we usually see avalanche activity.
Detailed Forecast
A system will move mainly across Oregon and north California on Thursday night. This system should spread some moderate snow as far north as Mt Hood on Thursday night and Friday morning with way less in the Olympics and Washington Cascades.
Some snow showers should drift north over western Washington on Friday. Models vary on whether or not there will be a change to a light west wind  in the Cascade passes but this change will be indicated in the weather forecast along with a bump in the snow level for the central Cascades Friday afternoon. The snow showers should bring mostly light amounts of new snow in the Olympics and Washington Cascades and are not expected to cause a great change in snow conditions along the west slopes.
Avalanche problems should be mainly from layers formed during the snowfall seen about January 12-14th.
Wind slab from January 12-14th should be most likely on ridges and on north to southeast slopes near and above treeline. Watch for signs of hollow snow and firmer wind transported snow.
Storm slab where it might still exist from January 12-14th could linger on more varied aspects but should be becoming unlikely and should be stabilizing.
New wind or storm slab layers would be possible if there is more snow than expected on Friday. Be prepared to adjust your plans if you are out and find more than a few inches of new snow on Friday.
Snowpack Discussion
Extensive surface hoar formed prior to January 11th during fair weather on shaded aspects. Warming and rain on January 11-12 destroyed this layer on all aspects below about 5000 feet or the Below Tree Line Zone. However, initial snowfall during the afternoon of Jan.11th buried this surface hoar layer, of at least 2cm in many test pits, near and above about 5000 feet, Near and Above Treeline.Â
The buried surace hoar uncovered after stability test failure. Buried about 30 cm (1ft) below the surface on shaed terrain above 5000 feet. photo, Lee LazzaraÂ
This persistent slab has already produced numerous avalanches in the Baker area, Shuksan Arm and Canyon Creek area. These dangerous slabs have been triggered upon approach, remotely triggered with some causing sympathetic slides. Extensive field observations by NWAC observer Lee Lazzara in the Canyon Creek area Thursday, found this layer to be widespread, buried about 30 cm (1 ft) on non-wind loaded, shaded slopes above about 5000 feet. This layer is consistent with the many recent observations posted to NWAC on the observations page since January 13th and the many recent avalanches in this zone.
It's safe to say, backcountry travelers are likely to trigger dangerous avalanches on slopes steeper than about 35 degrees, ranging from West-North-East facing above about 5000 feet, especially Northerly facing!  In wind loaded areas, mainly near ridges, some of these slides could be 2-3 feet, indicated by the slides of this size recently triggered on Shuksan Arm, 1/13.
Obvious grey line in snowpit is the buried surface hoar layer, buried January 11th. Photo: Lee Lazzara
Below 5000 feet on all aspects, a strong rain crust now has varying amounts of recent lower density snow, ranging from about 4-8 inches and this is not causing any specific avalanche problem below treeline.
Avalanche Problems
Persistent Slabs
Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slabs.
The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.
Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Very 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: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1