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Avalanche Forecast

Archived

Dec 5th, 2016–Dec 6th, 2016

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, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

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A slow improvement should continue, but cold temperatures slow the settlement process and may preserve recent storm snow instabilities found on wind loaded aspects near and above treeline. In steep sheltered terrain, watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences.  

Detailed Forecast

Showers should end early Tuesday with a clearing trend and cold temperatures with light winds. This should allow for a further slowly improving trend in avalanche danger as any storm related weak layers further settle and stabilize. 

In particular, watch for lingering wind slab on lee aspects near and above treeline that can still be human triggered. 

In steep terrain where the new snow lacks a slab structure, watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences. 

Even though the lower part of the below treeline band is filling in, watch for early season travel hazards such as barely covered rocks and open creeks. 

Snowpack Discussion

Weather and Snowpack

A front crossed the Cascades Friday, but likely only produced an inch or two of new snow near the Cascade crest with no accumulations further east. Moderate westerly ridgetop winds continued on Saturday.

A much stronger front crossed the area Saturday night, depositing 8-10 inches recorded from the Harts Pass and Lyman Lake Snotels respectively, 7 inches at Holden and Blewett Pass and 3-4 inches at Mission Ridge through Sunday morning. This system also ushered in the coldest air mass of the season.  Cool light showers Monday has only added very light additional snow amounts. 

Avalanche problems should be confined to the most recent storm snow and  we are not tracking any weak layers in the lower or middle of the snowpack at this time.

Recent Observations

The most recent observations from near Washington Pass Sunday, indicated a favorable snowpack profile with no triggered avalanches noted and good bonding to the older snow layers. Some minor wind effects were noted but most areas lacked slab character, with excellent conditions noted!

During midweek NWAC pro-observer Jeff Ward was in the Washington Pass area and found generally good ski conditions and a stable snowpack. Stubborn and shallow wind slab existed near and above treeline. Thin coverage and open creeks continued to be a travel hazard at the pass elevation. 

On Friday Jeff was out again at Jove Peak east of Stevens Pass, which can be representative of the eastern slopes closer to the Cascade crest. He saw no signs of instability, but noted minor wind transport along the ridge.

In general, more snow is needed in the Mission Ridge area to present an avalanche hazard. In wind-loaded terrain near and above treeline, no weak layers of note have been reported by the pro-patrol through Saturday. 

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 Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.