Avalanche Forecast
Regions: Cascades - North West.
Natural avalanche should become isolated or end by early Wednesday as temperatures cool and precipitation relents, but dangerous avalanche conditions linger. A fresh storm slab sits on either a refreezing upper snowpack or adds to a 3-4 ft existing storm slab if you venture above 5500 ft. With uncertainty surrounding how quickly the snow will heal, and serious danger from slopes above, stay safe by avoiding open slopes steeper than 35 degrees.
Discussion
Take a moment to appreciate the magnitude of this event. Mt. Baker Pro Patrol reported widespread size 2-2.5 and even some size 3 avalanches ran naturally Monday and Tuesday, with numerous large avalanches also released by mitigation at the ski area. Significant features on Shuksan Arm, Hemispheres, and in Bagley Lakes all ran long distances.
Since the last rain crust formed at the end of the evening last Friday 01/03, Mt. Baker (Heather Meadows) added about 40†to their snowpack, before the snow changed to rain as the snow line crept up to 6000 ft on Tuesday. This addition of snowpack came with about 6†of water with two inches of rain received on Tuesday; making for an impressive 13†of water equivalent since 4 AM on 12/31. The primary driver of the intense avalanche cycle was the volume of snow, but secondarily, the avalanches were more reactive because Monday’s low-density snow was rapidly loaded by an increasingly heavy slab. Rain ultimately completed the widespread cycle, changing the character of the avalanches. By Tuesday, the wet avalanches were gauging 3-4 ft deep through the entire volume of snow since last Friday.
Snowpack Discussion
New Regional Synopsis coming soon. We update the Regional Synopsis every Thursday at 6 pm.
Avalanche Problems
Storm Slabs
We expect another foot of snow to form a storm slab overnight at Mt. Baker with cooling temperatures, initially strong winds, and high snowfall rates. Above 5500 ft, the pre-existing dry storm slab needs time to adjust to the continuous loading and wind-drifting through Tuesday night and you could trigger large avalanches within Tuesday night’s snow or very large avalanches that break down to Friday night’s crust. Below 5500 ft, a storm slab should sit on a refreezing upper snowpack. Uncertainty remains regarding how quickly the wet layers will refreeze and the thicker slab at upper elevation will lose reactivity. Don’t try to thread the needle. Large avalanche slopes and slopes 35 degrees and steeper should be avoided on Wednesday.
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