Avalanche Forecast

Here we go again! With another round of light to moderate snow forecast Saturday night, followed by perhaps a brief break Sunday morning and then with renewed light snowfall Sunday afternoon, 24 hr snowfall totals along the east slopes through Sunday 4 pm should average 3-12 inches with the highest totals in the northeast zone near the Cascade crest. Snow levels should remain relatively stable on Sunday. W-SW transport winds should stay moderate especially for the central-east and southeast Washington Cascades.  

With this latest round of snowfall, we are betting that we have arrived at the breaking point where avalanche activity becomes widespread, with natural avalanches likely and human triggered very likely. Wind loading of lee slopes will push the avalanche danger to High near and above treeline, but expect sensitive conditions in all bands. Less snowfall in the central and southeast zones will likely keep the avalanche danger a notch lower in these zones. 

Additional snowfall at moderated temperatures will aid in a more uniform slab structure throughout the east slopes, leading to soft storm slabs potentially failing on weak persistent grain types formed prior to this storm cycle. Storm slabs that initially fail within the new storm snow can step down to these increasingly deeper layers. Remote triggering of avalanches is possible with this snowpack structure. Choose low angled terrain and avoid slopes connected to avalanche paths with wind loaded start zones.

Expect new wind slab near and above treeline in all zones especially on lee easterly aspects. Avoid all wind loaded terrain Sunday. In areas away from the crest, such as Blewett Pass and Mission Ridge, expect wind slab to be the primary avalanche problem on lee aspects near and above treeline. 

Loose dry will not be listed as 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 many wind protected areas, there is an increased 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.

Weather and Snowpack

An active and cool weather pattern has resulted in a snowy December thus far with NWAC stations along the east slopes recording about 1 to 3 feet of snow.

Cold and fair weather took hold midweek. During this time, there have been many reports of right side up, favorable density profiles with lower density snow nearer the surface. The Washington Pass area in particular has enjoyed excellent skiing and riding conditions with good stability and light winds. Widespread near-surface faceting and surface hoar formation had been observed particularly in this area of the east slopes. The Mission Ridge area experienced moderate easterly winds through Thursday night before switching to moderate westerly winds early Friday morning. Moderate westerly winds continued at Mission Ridge on Saturday. 

Light to locally moderate snowfall accumulated Thursday night through Saturday morning along the east slopes. Mission Ridge and Blewett Pass saw a few inches each day, but Holden Village and the Lyman Lake Snotel showed about 12-20 inches of new respectively. In the Southeast zone, Snotels averaged about 6-12 inches of new snow over the last 2 days ending Saturday morning.  A slow warming trend began Friday night and continued on Saturday, gradually dislodging the previous arctic air mass.  

Recent Observations

Pro-observer Jeff Ward was in the Washington Pass area Friday and reported up to 25 cm (10") of new snowfall at Pass level by Friday afternoon. The new snow was of lower density but cohesive enough that easily and remotely triggered soft slabs were possible on all aspects with rapidly decreasing stability.

Mission Ridge pro-patrol reported the switch to westerly winds had loaded NE aspects below ridgetop on Friday. Easy to trigger wind slabs of 40 cm deep were observed on NE aspects around 6700 feet. Just a few hundred feet below in less wind affected terrain, the snowpack was generally right side up and lacked a cohesive slab. Avalanche concerns were confined to loaded slopes just below ridges again on Saturday in the Mission area. A shallow snowpack still locally limits the avalanche danger to the higher elevations and more wind loaded aspects.