Avalanche Forecast
Regions: Cascades - North West.
Very large natural and triggered avalanches are being reported Saturday. Avalanches in this zone should be large to very large and backcountry travel is not recommended Saturday.
Detailed Forecast
Decreasing winds and mostly light to moderate snow showers should be seen over the Cascade west slopes on Saturday with much lower snow levels and much cooler temperatures.Â
Large unstable storm and wind slabs should persist Saturday. Natural or triggered avalanches will remain likely to very likely. Avalanches should be large to very large.
Very dangerous avalanche conditions.
Travel in avalanche terrain is not recommended.Â
Snowpack Discussion
Weather and SnowpackÂ
...Updated 115 PM. Mt Baker area received over 2 feet of new snow as of Saturday morning. Reports of natural and human triggered large avalanches, many 3-5 foot crowns! In the Mt Baker backcountry, Mt Herman, 4-5' triggered slide released nearly 1/4 wide, including a partial burial.
The most recent wet warm storm arrived on Valentines Day 2/14 and formed the uppermost, very strong rain crust in the snowpack.Â
A series of disturbances in cool, NW flow aloft from Saturday 2/25 through Tuesday 2/28 deposited 1.5 - 3.5 feet of snow along the west slopes of the Cascades. Very strong alpine west winds were seen in most of the Olympics and Cascades on Tuesday.
Southwest flow aloft began to ramp up again on Thursday as the first in a new series of fronts crossed the Northwest. Strong southwest flow is carrying a second stronger front across the Northwest on Friday evening. Along the Cascade west slopes this will be causing strong southwest alpine winds, heavy, moist, dense new snow above about 3-4000 ft and wet snow or rain below about 3-4000 ft. An avalanche cycle is expected in many areas along the Cascade west slopes Friday afternoon and evening.
Recent Observations
North
Updated 115 PM Saturday - Widespread natural and triggered large avalanches, many 3-5 feet crowns with wide propagation on Shuksan Arm. Partial burial reported from triggering a slide on Mt Herman, a crown of 4-5 feet by 1/4 mile wide! Fortunate outcome. Â
NWAC observer Lee Lazzara reported that extensive avalanche control was needed at the Mt Baker ski area on Friday but further detail are not currently available. Lee found an upside down warmer, wetter over drier, weaker profile and that test columns were failing on isolation in storm snow layers. A general top of the snowpack profile was 30-40 cm of 1F+ over 4F snow.
Central
NWAC observer Jeremy Allyn was in the Alpental Valley on Thursday and found storm snow instabilities still present and slowly stabilizing. Thin wind slab was forming in the upper portion of the below treeline band and showed signs of increasing sensitivity.
The Stevens patrol reported widespread 6-8" ski triggered storm slab on Friday morning. Sensitive loose wet ski tests were also seen below about 4500 ft.
NWAC observer was also at the Stevens ski area on a day off from the NWAC but reported upside down wetter over drier snow conditions.
Extensive 4-14" wind slab triggered by explosive control turned into wet debris at Alpental on Friday morning.
South
No recent observations.
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: Likely
Expected Size: 1 - 2
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, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2