Avalanche Forecast

On Thursday, increasing clouds in the morning will bring a chance of light rain, freezing rain (in the passes) or high elevation snow in the south Cascades in the afternoon, potentially reaching the central Cascades during daylight hours. Temperatures should remain mild, but clouds should limit solar warming on solar slopes on Thursday. Easterly flow should keep the passes cool.

Lingering wind slabs are expected to continue to become less sensitive to triggering Thursday. Solar radiation of recent snow has helped wind slab to heal on SW through SE aspects, where this concern has been removed. Continue to watch for areas of recently wind transported snow such as fresh cornices, snow drifts, and uneven snow surfaces. Identify and avoid locations where recent wind loading occurred.

Wind slabs can be deceptively difficult to manage in the terrain. Take a moment and read our recent blog post by NWAC Pro Observer Jeremy Allyn on wind slabs.

Cornices along ridge crest in the west slopes of the Cascades and Passes have grown quite large especially at higher elevations on some ridgelines. Remember to give these features a wide berth. Cornices can break much farther back from the ridge than expected.

In many areas, firm surface crusts will make for difficult travel conditions so be prepared to self-arrest and think about the sliding hazard before crossing steep slopes.  

Despite all this new snow, early season hazards still exist. Many creek beds have still not filled in for the winter.

Mild weather seen Sunday through Wednesday has allowed lingering wind slabs to gain strength. Temperatures have been cooler in the Passes due to shallow easterly flow, slowing the pace of stabilization in these areas, but there has been no recent human-triggered avalanche activity. Small loose wet slides were noted in steep terrain features on solar slopes.

Winds Saturday formed shallow slabs on a variety of aspects near and above treeline throughout the west slopes. Depending on elevation these wind slabs sit on soft snow storm snow or firm rain crust. Shallow wind slabs were triggered by recreational skiers on Sunday in the Snoqualmie and Mt. Baker backcountry. 

The Dec 28th/29th storm cycle formed a rain and/or freezing rain crust throughout the west slopes of the Cascades including the Passes that reached at least into the near treeline elevation band. Rain was reported to 6500' at Crystal and 6000' at Mt. Baker. A few inches to a foot of snow fell at the tail end, with the most snow at Mt. Baker. 

These firm crusts capped storm snow which fell earlier during the storm cycle. Below the 12/30 crust (date the crust was buried), a generally strengthening snowpack can be found. Weather stations from across the region confirm the upper snowpack is settling.

Observations

North

NWAC Pro observers were on Shuksan Arm on Wednesday. They found no recent avalanche activity, but plenty of avy debris from 12/29. A melt freeze crust was present on all aspects with variable thickness. The rain crust was observable on all aspects down approximately 8".

Central

On Wednesday, an avalanche professional was on Rock Mountain and targeted a NE aspect at 5300' just below a ridge where wind slab was reactive ECTP18 on sharp looking decomposing fragments. A small wet loose avalanche cycle did occur during the day on solar aspects above 5,000'. Snow was getting eroded from E winds in the above treeline zone. Below 4000' faceting was on the surface, both above and below crust with the inversion. Lower elevations east of Stevens saw sun for the first time in days.

On Wednesday, a NWAC forecaster was in the Alpental backcountry and noted an overall strengthening snowpack. The top 4" of snow is poorly bonded to the 12/29 0.5" freezing rain crust lying over and surprisingly poorly bonded to the underlying rain crust. Both crusts were supportable. Travel was very difficult with loose snow over a very firm, slick bed surface! Small loose wet slides were on SW through SE aspects under steep, rocky, sunny slopes. Wind slab was not observable as a problem, but cannot be completely ruled out in the alpine. Significant debris from the widespread large and very large slide cycle from 12/29 was evident throughout on slide paths throughout the Source lake drainage.

On Sunday, Stevens Pass Patrol described a freezing rain event to the top of the ski area that occurred Friday night. Winds Saturday formed shallow wind slabs within the area. Approximately 4” of soft snow sits above the freezing rain crust in wind sheltered areas.

South

On Wednesday, Professional Observer Ian Nicholson was in the Crystal backcountry and found breakable crusts and sun-affected snow.  Steeper solar slopes were capable of producing huge roller-balls but dry snow remaining on NW through NE aspects. He did get a rather stiff wind slab to break cleanly down 20 cm on a specific terrain feature near treeline.