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Avalanche Forecast

Archived

Jan 12th, 2018–Jan 13th, 2018

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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Mild weather will continue to allow wind and storm slabs to gain strength Saturday. This process takes time. Keep an eye on changing weather conditions and their impacts on the surface snow. Be ready to adjust travel according to a developing loose wet avalanche problem as skies clear and the sun comes out.

Detailed Forecast

Precipitation will taper off Friday night and Saturday morning.  Mild weather Saturday will continue to allow weaklayers in the snowpack to gain strength. This takes time.

Wind slabs are expected to linger near and above treeline. Looks for and avoid areas where winds have recently deposited snow such as fresh cornices and wind drifts.

Storm slab avalanches observed over the past few days have failed within the recent storm snow. As these layers gain strength they will become less likely to trigger, but if they fail they could propagate widely across terrain.

Warm air temps and clearing skies will allow moist to wet surface snow to develop of sunny slopes. Watch for changes in the weather and anticipate surface snow changes. This is most likely in the southern end of the forecast area, but could occur in any region.

Despite the recent snow, early season hazards still exist. Many creek beds have still not filled in for the winter.

Snowpack Discussion

A mild day with some light showers seen mainly near the Cascade crest on Friday continued to allow wind and storm slabs weaknesses to heal.

This week’s storms brought 8-14 inches of snow to the east slopes of the Cascades. Snow piled up quickly in many areas. This likely resulted in a natural avalanche cycle releasing within the new snow. Winds throughout the stormy periods redistributed snow, forming wind slabs on a variety of aspects especially in exposed terrain.

The supportive 1/5 crust formed from a widespread freezing rain event in the central-east zone, extending to the Stevens and Snoqualmie Pass areas. This layer is not present in the northeast from Washington Pass to Holden.

Snowdepth still decreases substantially the further east of the Cascade crest one travels. In many areas below treeline, there has not been enough snow to present an avalanche danger but Thursday's storm may have expanded potential avalanche terrain to lower elevations.

Observations

North

Guides from both North Cascades Mountain Guides and North Cascades Heli were in the field Friday. Observations suggest storm snow weaknesses are gaining strength. Very light snow showers and overcast skies allowed cold surface snow to remain on nearly all slopes. Also on Friday, NCH observed evidence of a widespread natural storm and wind slab avalanche that had occurred Thursday or Thursday night.  

Central

Mission Ridge Pro Patrol Friday reported upside-down new storm snow. Avalanches observed failed within the storm snow.

Older but still relevant observations:

A public observation from 1/5 in the Mission Ridge backcountry noted a 1/4" thick freezing rain crust up to 5000'. 

Basal facets (2-3mm) observed on 1/2 above 5000' on NW-N-E aspects and failing in snowpit tests in the Blewett Pass area (and likely the Mission Ridge area) will need to be watched when enough snow returns to this area to create a potential avalanche problem.  A more recent observation of the basal facets in this area can be found here.

South

No recent observations

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Loose Wet

Loose Wet avalanches are the 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. 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.