Avalanche Forecast

A low pressure and frontal system should pass by to the south across Oregon and north California on Wednesday. It looks like this will system will cause light to moderate southeast winds in the Cascades and mostly light snow over the south Cascades on Wednesday.

Overall the avalanche danger will be less on Wednesday than the past few days. But small areas of new wind slab might be possible depending on the strength of the east to southeast winds.

New wind slab should not be extensive as east to southeast winds are not expected to be strong on Wednesday. Since older wind slab is still possible on mainly north to southeast aspects and new local wind slab is possible on northwest to west aspects, wind slab will be indicated on all aspects. Watch for firmer wind transported snow which would be be more extensive if winds are stronger than expected.

Storm slabs from the recent storm cycle will further settle on Tuesday.

There is still uncertainty regarding the regional extent, spatial variability and the stability of the potential December 8th persistent weak layer which would be buried at about 2-4 feet along the west slopes. Ratchet back your plans if you experience collapsing or whoomping. Further time and snowpack tests from many areas will be needed to determine is this layer is still a regional problem.

Loose dry avalanches will not be listed as an avalanche problem on Tuesday. But in steep terrain lacking a slab structure continue to watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences. 

With deep unconsolidated snow in many wind protected areas there remains a risk for tree well and snow immersion suffocation at this time. Ride or ski with a partner and keep them in sight at all times!

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.

The regional avalanche danger is expected to further slightly decrease on Thursday.

Weather and Snowpack

Cold and fair weather early last week allowed for a sun crust to form on many solar aspects and for cold low density snow, near surface faceting and/or surface hoar to become fairly widespread.

These layers began to get buried in most areas on about December 8th when the latest storm cycle began starting with a couple day warming trend as southwest flow eroded an Arctic air mass over the Northwest. This initially buried the cold low density snow, near surface faceted snow and/or surface hoar with denser snow in most areas. The warming trend leveled off with temperatures staying well below freezing on December 10th and 11th and snowfall tapered off by December 12th. NWAC stations along the east slopes had about 1-3 feet of snowfall for the 4 days ending Monday morning.

Recent Observations

A regional avalanche cycle was seen about Thursday to Sunday with some avalanches releasing on the December 8th layer.

Observations from Washington Pass Saturday indicated about 12 inches of storm snow was still lacking much slab character but had gained minor slab stiffness in areas. One natural size 1.5 wind slab was noted releasing from below a ridge. No triggered slides were reported but some cracking was noted as the surface snow gained some cohesion.  The December 8th layer of buried surface hoar and/or buried near surface facets was about a foot down as of Saturday.

An observation for the Mission Ridge via the NWAC Observations tab for Sunday in the Lake Marion area indicates a right side up snowpack but also spatial variability and 10-35 cm wind slab giving shooting cracks on loaded slopes.

Pro-observer Jeff Ward was at Washington Pass on Sunday and  noted slightly increasing slab structure near ridges above about 7000 feet with some cracking and limited propagation when testing steep convex slopes.

The pro-patrol at Mission Ridge on Monday gave a very similar report to the Lake Marion report above, that of a generally shallow but stable snowpack but with spatial variation and where steep wind loaded on north to east slopes slopes had a sensitive snowpack.