Avalanche Forecast
Regions: Snoqualmie Pass.
Shallow storm slabs are possible Monday mainly near and above treeline. Watch for new snow received Sunday and Monday afternoon that has bonded poorly to old surface crusts or in areas of preserved surface hoar.
Detailed Forecast
Generally very little precipitation is expected Monday morning, with light rain and snow increasing during the afternoon along the west slopes. The Cascade Passes will locally stay cooler through Monday afternoon thanks to cool easterly flow. A frontal passage is expected later Monday afternoon, switching the Pass winds to westerly and popping snow levels up to free-air levels of 5500 ft.
Shallow storm slabs formed Sunday and Monday may have bonded poorly to old surface crusts especially near and above treeline. New storm slabs, still very shallow, may also fail on surface hoar that was recently buried on shaded aspects generally below treeline. Small loose wet avalanches can't be ruled out below treeline Monday afternoon.Â
The Mt. Baker area will have a higher avalanche danger and will be broken out from the other west side zones.Â
Snowpack Discussion
The weekend of Jan 24-25th, a warm and wet weather system caused high snow levels and rain and allowed for extensive snowpack settlement. Last week, high pressure aloft caused abundant sunshine and mild temperatures. A frontal system crossed the PNW on Sunday, producing generally light amounts of new snow, except moderate amounts in the Mt. Baker area above 4-4500 feet. Moderate S - SW winds likely built new wind slab near and above treeline in the Mt. Baker zone as well. Â
Prior to the Sunday's system, the snowpack was dominated by strong surface crusts, limiting the avalanche potential. There had been surface hoar growth last week on shaded terrain mainly below about 5000 feet, along with some near surface faceting(NSF) on non-solar slopes. Surface hoar/NSF were likely buried by the light snowfall and initial cool temperatures Sunday.Â
See Jeff's video from the Steven's Pass area below.
The snowpack west of the crest should mainly consist of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.
Avalanche Problems
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
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.
Elevations: Below Treeline.
Likelihood: Unlikely
Expected Size: 1 - 1