Avalanche Forecast

A very important pattern change is taking place over the Northwest Friday and Saturday. The dry weather and strong cold E-NE winds seen Wednesday and Thursday are being replaced by increasing strong southwest flow aloft, increasing snow and warmer temperatures Friday and Saturday.

Saturday should be a day of strong southwest alpine winds, with a change from cool east winds to warmer west winds in the Cascade Passes, moderate to heavy snow with snow changing to rain at lower elevations, and warming temperatures.

Along the west slopes at higher elevations from Friday to the end of the day on Saturday there should be 1-2 feet of warmer, denser new snow. This will generally build new upside down wind and storm slab layers. This new snow may build over weak or faceted snow from the cold weather mid-week on some or many slopes.

This is a recipe for avalanches.

An avalanche warning has been issued for the west slopes for Saturday.

New sensitive wind slab is very likely on NW to SE slopes but will be found on other aspects especially in the Cascade passes due to wind shifts there.

Wind slab formed by strong E-NE winds on Wednesday and Thursday may linger on Saturday. The primary aspects for these wind slabs should be W facing slopes.

New sensitive potentially deep storm slab will continue to build on sheltered slopes on Saturday in areas that see rapidly accumulating snow. The warming trend will help build upside down layers and promote storm slab formation.

Natural or triggered wind and storm slab avalanches are very likely along the west slopes on Saturday. Wind or storm slab avalanches may step to deeper layers. Rain at the lower elevations may also trigger loose wet or wet slab avalanches on Saturday.  Travel in back country avalanche terrain is not recommended along the west slopes on Saturday.

Weather and Snowpack

An atmospheric river arrived over the Northwest on 1/17 forming a rain crust in most locations below 6000-7000 feet and with freezing rain in the Cascade Passes.

A storm cycle from Thursday to Sunday, 1/22-1/26 deposited 1-2 feet of snow along the west slopes of the Cascades with the greatest totals seen at Mt. Baker.

A large upper ridge and warm air mass built over the Northwest last Thursday to Saturday 1/26-1/28 with temperatures reaching the 40s in many places along the west slopes away from the lower parts of Stevens and Snoqualmie.

Very strong NE-E winds were seen Wednesday and Thursday with very cold temperatures. Fresh, touchy wind slabs formed with large plumes of snow visibly transporting loose snow from exposed terrain.   

Recent Observations

North

The NWAC received an observation last Saturday 1/25 describing 2 groups of skiers who triggered 3 separate wind slab avalanches with depths averaging about 2 feet in the Mt. Baker backcountry. The wind slab avalanches were triggered on N through E slopes between 5000-5800 feet on Mt Herman with one slide burying a skier waist deep. Fortunately the skier involved was not injured.

Lee was on the south side of Mt Baker Wednesday and experienced the rapidly forming touchy wind slabs on a variety of aspects. One natural wind slab released Wednesday on the eastern side of the Metcalf Glacier. The strong winds were predominantly easterly but wind slabs were forming on a variety of aspects, including cross loaded slopes and other specific terrain features. 

Central

Both Tom Curtis and Jeff Ward traveled Wednesday independently in terrain east of Stevens Pass, covering the areas of Rock Mountain, Jove and Union Peaks. Both reported rapidly forming, very touchy wind slabs by mid-morning. Plumes of wind transported snow were seen along all ridges and exposed terrain Wednesday. Wind slabs were building much further downslope due to the strength of the winds. Wind slabs up to 12" were seen and noted forming well below treeline. Any small feature or convexity would produce shooting cracks or release small wind slabs, even on relatively shallow angled terrain. Both avoided travel on any steep terrain.

The Crystal Mountain pro-patrol on Friday morning reported sensitive mostly shallow new wind slab due to wind, snow and warming which was up to 1 foot deep in areas where loading was more focused below ridges.

The Alpental pro-patrol Friday morning reported lots of wind transport and shallow new wind slab forming over weak snow from the cold weather mid-week.

South

NWAC pro-observer Dallas Glass was at Paradise on Friday and found warmer than expected weather. He noted no significant signs of instability and no avalanches, with minor cracking on a steep small test slope.