Avalanche Forecast
Regions: Snoqualmie Pass.
The Bottom Line: Concerns should be limited on Sunday. Check or take precautions for isolated small areas of slab layers on lee shaded slopes or for small areas of wet snow on steep solar aspects.
Detailed Forecast
Another sunny warm day with light winds should be seen on Sunday. There should be little change in snow conditions.
Concerns on Sunday should be very limited. Small areas of slab layers may linger on some lee shaded slopes mainly near or above treeline. Such layers would likely require large triggers such as a fall cornice or snowmobile. Use more caution and analysis before committing to steep lee shaded slopes.
Wet loose avalanches seem unlikely on Sunday due to recent consolidation, past activity, limited solar input and increasing surface crusts. But avoid steep solar aspects or gullies in the sun if you seen natural wet loose avalanches or wet surface snow deeper than a few inches.
Snowpack Discussion
The last storm cycle to impact the Northwest was about 10-14 of January.  The storm produced about 1.5-4 feet of snow at most NWAC sites near and west of the crest. The tail end of the storm cycle 12-14 January brought a warming trend that caused rain at low and mid elevations and upside down heavy dense snow at higher elevations. A storm slab avalanche cycle was seen on 12 January and large wet loose avalanches were seen 14 January with avalanches ranging from size D2 to D3. Â
Mostly sunny weather and warm temperatures have been seen the past 11 days. This has mainly caused snow pack consolidation and stabilizing with surface crusts on most slopes in most of the area. A generally favorable mid and lower snowpack of crust layers and melt form crystals should also be seen in most of the area. The avalanche danger is low at lower elevations where there is little snow and ample terrain and vegetation anchors (see photo below). There have been no avalanches reported the past few days.
Small areas of cold slab layers are still apparently surviving on some lee shaded slopes where some faceting has been occurring in the upper snowpack.  NWAC observers at Hurricane and Nason Ridge near Stevens Pass the past several days are reporting moderate or hard test results with sudden collapse or sudden planar fractures (see photos below). Extended column tests have not indicated a tendency for propagation. These layers would also likely require large triggers such as a cornice or a snow mobile. There have been no known avalanches on these layers but we will continue to monitor them in case future changes or loading activate the layers.
Widespread reports of surface hoar growth has been reported this week but will have to withstand additional sunshine, warm temperatures and winds to become an issue when we finally receive more precipitation.Â
ECTP29 SC Q1 at 67 cm due to crust and facet layers, Nason Ridge. NWAC observer Tom Curtis, 20 January.
Faceted crystals from the upper snow pack, Klahhane Ridge near Hurricane Ridge, NWAC observer Katy Reid, 20 January.
South slopes of Klahhane Ridge, Olympics - still awaiting winter! NWAC observer Katy Reid, 18 January.
Report of the cornice/avalanche fatality on Lewis Peak on 18 January available at https://www.nwac.us/accidents/accident-reports/Â
Local non-avalanche hazards:  On 13 January a heavy local freezing rain event occurred in the Snoqualmie Pass area above about 4500 feet, covering the surface with about a 2-3 inch ice crust.  This crust should break down over time but a fall on a slope on this surface could result in a long and dangerous ride!
Additionally, guides in the North Cascades have noted some thin crevasse bridges on lower glaciers. Don't assume that crevasses have the usual relatively thick bridges during this shallow snow season.
Avalanche Problems
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.
Likelihood: Unlikely
Expected Size: 1 - 1
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: Alpine.
Likelihood: Unlikely
Expected Size: 1 - 1