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Avalanche Forecast

Archived

Jan 5th, 2016–Jan 6th, 2016

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

Regions

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A variety of avalanche problems are expected on Wednesday. Dangerous avalanche conditions are possible on Wednesday due to likely new storm slab and potential weak layers from around New Years. This forecast errs on the side of caution until more information becomes available.

Detailed Forecast

A large weak low pressure system will drift toward California on Wednesday. A shot of drier air with some weak light showers should eject from the low and over the Northwest. Slightly warmer temperatures should be seen in most areas.

There is some uncertainty in the avalanche danger forecast for Wednesday and this forecast will err on the side of caution until more information becomes available. The storm snowfall of 5-15 inches along the east slopes may be somewhat upside down with denser snow near the surface and will lay over surface hoar and near surface faceted snow from around New Years in many areas. This should make triggered storm slab likely on Wednesday. Small avalanches in many areas or large avalanches in specific areas should be expected Wednesday until more information becomes available.

Mostly older wind slab will still need to be watched for on a variety of aspects. Wind slab from over the weekend is most likely on west aspects. Look for signs of firmer wind transported snow that can indicate wind slab layers.

Some sun or solar effects and slightly warmer temperatures should also be seen on Wednesday. Loose wet avalanches seem like an unlikely bet as well on steep solar slopes. Watch for wet snow deeper than a few inches and initial natural small loose wet releases on solar slopes that usually precede loose wet avalanches.

Snowpack Discussion

Fair weather was seen for almost a week around the New Year. This weather caused lots of consolidation and stabilizing of the snow from December. It also caused extensive surface hoar and near surface faceted snow on non-solar sheltered slopes according to reports for west and east of the crest in the Washington Cascades.

Tom Curtis was west of Blewett Pass around Iron Mountain New Years Day and found the December 13 buried surface hoar layer 60 cm down that showed sudden collapses in several column tests, including PST with a firm slab overhead. In this area, the layer was prevalent on NE-E aspects around 5300 ft near treeline. This may be a layer of concern to track or look for moving forward in this specific area. 

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

The North Cascades Mountain Guides on January 1st and 2nd at Washington Pass generally report good stable conditions and a lack of results in snow pit tests. Minor wind effects have been noted near ridges.

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 help confirm the extent of hoar frost from around the New Year.

A change Sunday night to Tuesday has been some snow and a bit of a warming trend. Storm snowfall for this period should range from about 5-15 inches by Wednesday along the east slopes. Heads up because this new snow may accumulate on surface hoar and near surface faceted snow from around the New Year on many non-solar or sheltered slopes!

 

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.

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.