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Avalanche Forecast

Archived

Jan 10th, 2016–Jan 11th, 2016

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

Regions

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New small shallow storm and wind slab seems possible by the end of the day on Monday mainly above treeline. Evaluate snow and terrain carefully on Monday. Adjust your plans if winds are stronger or new snowfall is heavier than expected.

Detailed Forecast

A front should weaken as it moves over the Northwest on Monday. Over the west slopes this should bring moderately increasing southwest alpine winds and mostly light occasional moderate rain or snow Monday morning changing to showers Monday afternoon with lowering snow levels.

Any wet surface snow from Sunday should refreeze on Monday. 

Light new snow amounts should be seen east of the crest by the end of the day.

New small areas of shallow storm slab seem possible mainly above treeline east of the crest by the end of the day. The limited amounts of new snow and the cooling trend should greatly limit the extent and depth of new storm slab by the end of the day.

New small areas of shallow wind slab also seem possible mainly on lee slopes mainly above treeline by the end of the day. The limited amounts of new snow and the cooling trend should also greatly limit the extent and depth of new wind slab.

 

Snowpack Discussion

Fair weather for about a week over the New Year caused extensive surface hoar and near surface faceted snow. Then about 4-13 inches of snowfall over the east slopes last week buried the surface hoar and near surface faceted snow.

Tom Curtis was west of Blewett Pass on Iron Mountain on New Years Day and a December 13 buried surface hoar layer 60 cm down that showed sudden collapses and propagation in several column tests with a firm slab. In this area the layer was prevalent on northeast to east aspects around 5300 feet near treeline. This may still be a layer of concern to track going forward in this specific area but no further reports have been received. This layer is likely gaining significant strength due to the mild temperatures this week.

PST End down, 60cm on 20151213 buried surface hoar layer. West of Blewett Pass, January 1, 2016. ENE aspect NTL @ 5330 feet. Photo: T. Curtis

Reports via the NWAC observations page for January 2nd at Blewett Pass, email received at the NWAC from Holden for January 3rd, reports via the NWAC observations page for January 4th for Stevens and Snoqualmie and for Red Mountain near Salmon La Sac on January 5th (which includes a video) help confirm the extent of the buried New Year layer.

The North Cascade Mountain Guides were at Washington Pass on Friday found that the recent storm snow was surprisingly well bonded to the previous snow is spite of surface hoar and faceted snow at the New Year interface. Tests and ski cuts gave no results due to little slab structure of the recent snow.

The DOT crew reported several small loose wet avalanches reached the shoulder of the highway on Saturday in Tumwater Canyon.

 

Problems

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.

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.