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Avalanche Forecast

Archived

Jan 9th, 2016–Jan 10th, 2016

Alpine
Natural avalanches unlikely, human triggered possible.
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.

Regions

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The main problem on Sunday should be loose wet avalanches. It is a bit hard to say how extensive the loose wet avalanches will be so pay close attention to snow conditions if you venture out on Sunday.

Detailed Forecast

Sunny warmer weather should be seen on Sunday. It may be significantly warmer at higher elevations east of the crest.

The main problem on Sunday should be loose wet avalanches. It is a bit hard to say how extensive the loose wet avalanches will be so pay close attention to snow conditions if you venture out on Sunday. Possible loose wet avalanches should be mainly confined to steep southeast to southwest aspects during the late morning to early afternoon hours. Watch for surface wet snow deeper than a few inches, initial roller balls and initial small natural  or triggered loose wet avalanches.

We have lowered the likelihood of triggering an older wind slab avalanche. But it will still be wise to watch for firmer wind transported snow on specific terrain features. The most likely locations are steep slopes below ridges mainly near or above treeline.

Some powder may still found out there on sheltered north slopes. Surface crusts will also abound to bring added enjoyment to your outing.

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. Weak surface layers were seen in numerous reports both west and east of the crest in the Washington Cascades.

Tom Curtis was west of Blewett Pass on Iron Mountain, New Years Day and found the 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 and further reports via the NWAC observations page for January 4th for Stevens and Snoqualmie, and most recently Tuesday the 5th on Red Mountain near Salmon La Sac (which includes a video) help confirm the extent of the recently buried surface hoar.

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 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

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.

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.