Avalanche Forecast
Regions: Cascades - West.
Choose conservative routes with plenty of options to navigate avalanche slopes and adapt to dynamic weather conditions Wednesday. Steer around any open slope greater than 35 degrees where you could trigger an avalanche. With snow levels near 3000 ft during much of this storm, expect instability to persist longer and avalanches to be larger at higher elevations.
Discussion
Weather forecasts indicate that this storm should pack quite the punch and aims the highest water amounts at the West Central zone Tuesday night. We expect around 1" of snow water equivalent to fall overnight in northern parts of the forecast zone by Wednesday morning (with lower amounts south of the Mountain Loop) and lighter snow showers becoming steadier snowfall by Wednesday afternoon adding 0.25-0.5" of snow water during the day. Although we probably didn’t get to considerable avalanche danger on Tuesday below and near treeline, with the high snowfall rates forecast, we should have plenty of snow to create new storm slabs. Rapidly accumulating snow needs time to settle, so it will be prudent to seek lower angle slopes.
Looking forward another day, very dangerous avalanche conditions should develop as snow intensifies and then changes to rain Wednesday night and we expect that danger will be present into the day on Thursday.
Snowpack Discussion
New Regional Synopsis coming soon. We update the Regional Synopsis every Thursday at 6 pm.
Avalanche Problems
Storm Slabs
You may trigger a storm slab on any open slope greater than 35 degrees. Potential avalanches could be larger and harder to avoid as you ascend in elevation to areas where a significant wind event in areas exposed to southerly winds on Tuesday drifted slabs deeper. Storm snow will accumulate above a thin but firm crust layer formed over the MLK holiday. So far, in the adjacent West North zone, observations indicate this new snow is bonding well to the crust, but not enough snow piled up to truly test this potential interface. That should change by Wednesday. Use small slope tests and shallow hand pits to investigate the storm snow and how it bonds to the MLK crust. If you encounter surprising results or find more snow than expected, step back and reevaluate your terrain choices. Avalanche danger should peak during periods of heavy snowfall and blowing snow.
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