Avalanche Forecast
Issued: Jan 6th, 2018 11:02AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Wind Slabs.
NWAC,
Northwest Avalanche Center
Shallow storm slabs may develop by the afternoon, particularly in the Mt. Baker and Paradise area. Watch for shallow fresh wind slabs near ridges at higher elevations, especially in areas that may have received greater amounts of new snow. Further warming forecast for Sunday night will increase the likelihood for loose wet avalanches below treeline.
Summary
Detailed Forecast
Light snow should begin Sunday morning and increase in the afternoon and evening, becoming locally moderate for the volcanoes including Mt. Baker and Mt. Rainier. A warming trend is expected along with the increase in precipitation with rain mixing in at Snoqualmie Pass in the afternoon. Precipitation should be quite light in the Crystal mountain area Sunday and for areas further south including White Pass. See the mountain weather tab for more details.
Shallow storm slabs may develop by the afternoon, particularly in the Mt. Baker and Paradise area. Watch for increasing snowfall rates as the day wears on.
Increasing SW alpine winds Sunday afternoon will begin to transport snow onto lee slopes at higher elevations. Approach lee slopes with caution above treeline on Sunday, watching for signs of active wind transport.
Loose wet avalanches will not be listed as an avalanche problem, but at lower elevations that see rain on Sunday, snowfall from Saturday will be available for small loose wet avalanches. Take care in steep terrain exposed to terrain traps.
Early season hazards still exist. Many creek beds have still not filled in for the winter.
Be cautious when travelling on slopes with an exposed slick surface crust due to fall hazard.
Snowpack Discussion
On Saturday, slow cooling, decreasing winds and generally light showers deposited 2-4 inches of new snow from late Friday night through Saturday afternoon along the west slopes of the Cascades including the Cascade Passes. Saturday's snow now overlies a rain or freezing rain crust.
This new snow followed light to moderate rain (except locally heavy in the Mt. Baker area) that reached up to crest level on Friday. Over at Stevens and Snoqualmie Pass, extensive freezing rain began overnight Thursday and continued through the day on Friday.
Reports indicate a strong upper snowpack with no notable layers other than the multitude of crusts formed over the last 10 days. Mild weather over the past several days has allowed for lingering weakness to gain strength, causing a diminishing avalanche hazard.
Observations
North
No recent observations.
Central
Professionals at the Alpental ski area and in the Alpental backcountry on Saturday reported the freezing rain crust as firm below 4500 feet and much softer to non-existent as one traveled higher in elevation. Little wind transport of new snow was reported. In a snowpit at 4500' below Pineapple Pass, the 12/30 crust was down 1 ft (30 cm). No avalanches were observed.
South
A professional in the Paradise area Saturday reported 4" of new snow well bonded to a stout melt-freeze crust with no new avalanche activity observed.
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
Expected Size
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: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Jan 7th, 2018 11:02AM
