Avalanche Forecast
Regions: Snoqualmie Pass.
The Bottom Line: The name of the game on Friday will again be wet loose on solar aspects. Little wind, plenty of sunshine and temperatures potentially a few degrees warmer than Thursday should again ramp up the prospect of loose wet avalanches in the late morning and afternoon.
Detailed Forecast
Solar influences will drive the avalanche danger on Friday. Be aware of quickly softening surface snow in the late morning and afternoon on solar aspects. Natural pin-wheels or sinking in more than ankle deep means it is time to get off and out of the way of steeper southerly slopes at all elevations. Still approach wind loaded slopes with caution, isolated wind slab may linger on N thru SE aspects near and above treeline zones.  Â
Widespread cornice growth was not reported during the most recent storm cycle, but be aware that local areas with cornices will be subject to the warming and sunshine and have an increased hazard during the day.Â
Snowpack Discussion
The most recent storm cycle to impact the PNW ended Tuesday after lasting for nearly a week with 2 - 4 feet (60 - 120 cm) of snow for the west slopes and added several inches of water weight to the snowpack. A fair amount of westerly wind accompanied the event from Friday through Monday and redistributed new snow onto lee slopes. The tail end of the storm cycle from Sunday afternoon through early Tuesday was accompanied by a warming trend that brought rain to mid elevations. The main avalanche activity with this cycle occurred last Sunday with large to very large D2 to D3 avalanches reported throughout the west slopes with start zones mainly in the near and above tree-line zones on wind loaded aspects. Natural avalanches released within the storm snow with isolated but larger slides up to 5' were produced by local ski patrols with explosives down to older crusts.Â
Tuesday through Thursday featured increasing temperatures and sunshine. The warmer and drier weather has allowed for snowpack settlement of about 6-12 inches since late Sunday. The new storm snow is generally well-bonded.  Surfaces vary from dense powder on northerly aspects...to wind crusts on lee aspects of higher terrain...to solar crusts on southerly aspects at all levels.  NWAC observer Tom Curtis on Wednesday from Jove Peak reported a sudden collapse and a clean shear in a compression test on an east aspect near-treeline.  However, this layer did not propagate in an Extended Column Test but suggests there may still be some touchy wind slab.Â
Photo by NWAC observer Tom Curtis on Jove Peak at 5400 ft
The warm and sunny weather has activated solar aspects with large wet-loose avalanches reported daily down through Wednesday into the below tree-line zone in the Stevens Pass area. Â
Photo from the Smithbrook area near Stevens on Tuesday by NWAC observer Dallas Glass and a short video of the wet loose slides:  https://www.youtube.com/channel/UCXKN3Cu9rnnkukkiUUgjzFQ
For the Olympics and west slopes of the Cascades a generally favorable mid and lower snowpack exists and is expected to consist of crust layers and melt form crystals. The avalanche danger is locally lower in the Olympics where the snowpack on windward and solar aspects near and below tree-line has less snow and ample terrain anchors. Â
Local non-avalanche hazard at Snoqualmie: In the Snoqualmie area on Monday, along with rain, a riming event produced a stout, supportable and extremely slick ice crust from about 4500 ft to the Alpental ridgetops above 5500 ft.  This crust should only be found on non-solar aspects near and above treeline. A slip on this surface would result in a long and dangerous ride!   Â
Avalanche Problems
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
Wind Slabs
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1