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Avalanche Forecast

Archived

Jan 7th, 2018–Jan 8th, 2018

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

Regions

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Shallow wind slab may be found on lee slopes near and above treeline. Small loose wet avalanches will remain sensitive to human triggering on Monday and possible on any steep slope regardless of aspect near and below treeline.

Detailed Forecast

Light rain and snow should linger the longest for the northeast Cascades on Monday morning, followed by a drying and clearing trend late morning through the afternoon. Freezing levels will be on the mild side. 

A natural loose wet avalanche cycle may have occurred Sunday night near and below treeline in many elevations and areas. Loose wet avalanches will remain sensitive to human triggering on Monday. Loose wet slides should be small in size, but possible on any steep slope regardless of aspect near and below treeline. 

Shallow wind slab may be found on lee slopes near and above treeline. Approach lee slopes with caution near and above treeline on Monday, watching for signs of recent or active wind transport.  

Small avalanches may travel further than you expect in areas that have an underlying and firm crust in the central-east and southeast Cascades, so avoid steep terrain exposed to terrain traps. Also, in the central-east and southeast Cascades, be cautious when travelling on slopes with an exposed slick surface crust due to fall hazard, mainly mid and lower elevations. 

Early season hazards still exist. Many creek beds have still not filled in for the winter.

Snowpack Discussion

On Sunday, light snow fell along the east slopes of the Cascades with a slow warming trend. Some light freezing rain may mix with light snowfall Sunday night. 

In the northeast Cascades, very light amounts of new snowfall have been noted at Snotels since late last week.  No freezing rain crust exists in ski terrain along the Hwy 20 corridor nor has buried SH been discovered in avalanche terrain.

Extensive freezing rain accumulated at mid and lower elevations along the central-east slopes of the Cascades as well as in the Stevens and Snoqualmie Pass areas Thursday night and Friday. This significant freezing rain event has likely destroyed or capped a variety of existing snow surface forms. The newly formed crust is limiting the current avalanche potential and formed over a relatively strong older snowpack. 

Snowdepth decreases substantially the further east of the Cascade crest one travels. In many areas below treeline, there is not enough snow to present an avalanche danger. 

Observations

North

On Saturday, NCMG noted a variety of surface conditions but no new avalanche activity outside of small loose avalanches in steep cliffy terrain. Isolated areas of shallow wind slab existed above treeline. No freezing rain crust was observerd along the Hwy 20 corridor. 

Central

A public observation from Friday in the Mission Ridge backcountry noted a 1/4" thick freezing rain crust up to 5000' making for treacherous travel conditions. 

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.  

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.