Avalanche Forecast

As precipitation transitions to rain Thursday, expect widespread wet avalanche activity. Wet loose avalanches should begin first as snow surfaces become wet and weak. These avalanches could build significant mass as they run downslope and pack quite a punch. With continued heavy rain on dry snow, the potential for wet slab avalanches may arise. The upper snowpack setup (dry snow above the MLK crust) and weather forecast are an ugly combination that checks off many boxes for a wet slab problem. Natural wet slab avalanches could occur if liquid water effectively percolates through dry storm snow layers and pools on the MLK crust. The best chance for this scenario to play out is between 4000-6000ft where:

1. The buried MLK crust is most pronounced

2. Enough dry snow sits atop the MLK crust

3. Significant rain on dry snow is expected

Wet avalanches are difficult to predict and act in surprising ways. Conditions will be dynamic and unmanageable on Thursday. Travel in or below avalanche terrain is not recommended. 

Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.

Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty

A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.

Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.

Additional snowfall will thicken existing slabs sitting above a crust formed MLK weekend. Natural storm slab avalanches are likely on slopes 35 degrees and steeper. Strong and gusty south winds will transport snow and load lee slopes creating stiffer and more reactive slabs. Avalanches could break within new/wind loaded snow, or involve all the recent storm snow above the MLK crust. Avalanche danger will peak during periods of heavy precipitation. Give the snowpack time to adjust. Avoid travel on or below slopes 35 degrees and steeper, and steer clear of large avalanche path run-out zones.

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.