Avalanche Forecast
Regions: Cascades - South West.
Conditions are changing in the mountains. Temper your excitement, choose conservative terrain, and ease into winter. The first major snow event of the season will bring several feet of snow, particularly in areas near Paradise, and increase the avalanche danger.
Discussion
Paradise is forecasted to receive more water than other areas in the zone, but the story remains the same throughout. A variable early season snowpack, with recent avalanche activity, will become buried throughout the forecast period. A natural avalanche cycle is possible during the height of the storm at higher elevations. Be conservative and ease into terrain by starting with small test slopes and evaluating what is happening with the snow. Tomorrow will be stormy with low visibility, it is not a good day to travel under features that you cannot see the top of. Recognize that until this storm, very low snow conditions existed, and early season hazards will persist despite the new snow.
This storm has the ability to change the avalanche danger quickly over space and time. With periods of high precip rates and fluctuating freezing levels, pay attention to how the storm snow sets up. Is it rightside up or upside down? Are there interfaces within the storm snow as winds or precip rates change? As the snow piles up, a day that starts out as moderate can develop into considerable quickly. Likewise, with high amounts of water forecasted, High avalanche danger could be reached by day’s end in the Paradise area. Anchors will become buried, and slab depth will increase throughout the storm. Pay attention to wind affected snow and look for collapses, cracks, and recent avalanches.
Lots of early season hazards at Rainier before the storm. Photo: Dallas Glass 12/8/19
Snowpack Discussion
Regional Synopsis Coming Thursday, December 12, 2019Â
Avalanche Problems
Storm Slabs
A few feet of new snow is forecasted to fall, making the formation of storm slabs likely on all aspects at all elevations. Slabs as deep as 3 feet, more than enough snow to bury a person, are expected. Changes in temperature, precipitation rate, and wind affect the bonding of snow. These bonds, whether in new snow, or at the old snow interface, will dictate the reactivity of storm slabs. Avoid traveling on slopes greater than 35 degrees when you find strong snow over weak snow. Below treeline, storm snow will be falling on a thinner existing snowpack, minimizing the avalanche danger.
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 - 1