Avalanche Forecast

A low pressure and frontal system will pass by to the south across Oregon and north California on Wednesday. This system will cause southeast winds in the Cascades, with east winds in the Cascade passes, and will cause some snow mainly in the south Cascades late Wednesday.

Light snow showers mainly along the west slopes and possibly to higher elevations along the east slopes should end Thursday morning with light winds and continued cool temperatures.

New local wind slab is possible on Thursday depending on the local strength of the east to southeast winds on Wednesday. This should be mainly on northeast to southwest aspects near ridges and passes in the central to south Cascades. Older wind slab from the latest storm cycle should have mostly stabilized so the northeast to southwest aspects will be indicated. But watch for firmer wind transported snow on all aspects mainly near and above treeline.

The Tuesday report from Stevens Pass indicates the December 8th layer is still possibly reactive in the Washington Cascades. It should be a good plan to stick to lower angle slopes and ratchet back your plans if you experience collapsing or whoomping or have evidence of this layer such as from snowpits. Persistent slab avalanches may be harder trigger but have a tendency to propagate to a larger size.

Storm slabs from the latest storm cycle should have mostly stabilized by this time. New snow amounts late Wednesday in the south Cascades should be limited enough to not build significant new storm slab. But change your plans if necessary if more snow falls late Wednesday than expected and you find you are in an area where there has been more than a few inches of rapidly accumulated snow and if it seems that storm slab might be present.

Loose dry avalanches from snow from the latest storm aren't expected to still be an avalanche problem. 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 sheltered areas there remains a risk for tree well and snow immersion suffocation. When near trees 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.

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 in the Washington Cascades.

These layers began to get buried 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 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 December 8th-11th with some avalanches releasing on the December 8th persistent weak layer in the Washington Cascades.

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.

The most important report from Tuesday is that another slab avalanche release on the December 8th layers was skier triggered in Highland Bowl back country next to the Steven Pass ski area. The Stevens pro-patrol reports it was on a steep SSW slope at 5400 feet with a 40 cm x 100 foot crown releasing in buried hoar frost and facets on a crust. If this layer is present at Stevens Pass it will be present along the Cascade east slopes.

A member of the Stevens Pass pro-patrol reported wind transport on Rock Mountain and especially in the Chiwaukums on Wednesday.