Avalanche Forecast

Persistent Slabs avalanches are difficult to manage. They have been the cause of fatalities or serious injuries for the past month in the Cascades. The best way to stay safe is to limit your exposure to terrain that can produce large avalanches. Stay out of avalanche start zones, terrain traps, and complex terrain in large avalanche paths. Watch out for shallower areas of snow where you can still trigger these avalanches. The potential for triggering Persistent Slabs takes a long time to go away and it's easy for the message to get old. Stay vigilant and maintain a wide buffer of safety between yourself and large, complex avalanche terrain.

Depending upon cloud-cover on Wednesday, solar exposed slopes may soften or may remain hard and slick. It may be difficult to stop a fall on these slopes while they are still firm. Avoid traveling near or under areas with glide cracks and stay away from large cornices. With continued mild temperatures below treeline, these types of terrain could be dangerous.

Expect mild temperatures with possible sun breaks in the morning, but increasing cloud cover later in the day. While there may be a few rollerballs with the solar radiation making it through thin clouds, Loose Wet Avalanches should not be a problem. Many sunny slopes have very hard crusts in the upper foot of the snowpack. High elevation, northerly slopes are staying soft and dry. You may see some localized drifts at upper elevations.

Below the most recent snow and crust, several older persistent weak layers continue to be reported. Persistent Slabs in the upper snowpack will be easier to trigger, but may be more isolated in their distribution. Persistent Slabs deeper in the snowpack (2/13 or 16 layer) are more widespread, but they are harder to trigger. Observations from the Eastern areas of the Cascades have found these layers reactive and 3 avalanche fatalities occurred on persistent weak layers in early March. The exact persistent weak layer depends on your location.

Commonly seen persistent weak layers are:

• Surface hoar and facets buried on 3/8. This layer is typically found 8-14" below the snow surface near and below treeline. Professionals near Washington Pass have reported that the surface hoar is fairly widespread in that area. The distribution of this layer may be more variable in the Central and Southern zones. 
• A more widespread persistent weak layer is found just above a firm crust layer buried on 2/5. This layer of weak sugary facets (2/13 or 16) can be found 2-4 feet below the snow surface. Professionals near Washington Pass and the north end of the East Cascades have reported that this layer most problematic below treeline.
• Other shallow and very weak areas of snowpack may be found further east of the crest or in areas with less snow.

Observations

North

On Tuesday, NCH traveled in the Washington Pass area reported 4 inches of new snow over a variety of surfaces with the 3/8 interface down about 10-14" with surface hoar or near surface facets on shaded aspects and a sun crust possible on non-polar aspects. The 2/5 rain crust extends up to 6800 ft in the terrain and the associated 2/16 PWL still produces sudden results in some locations.

Central

NWAC professional observer Matt Primomo traveled in the North Fork of the Teanaway River Thursday (just north of Cle Elum). Matt found 2-4 inches of new snow over a generally supportable crust. The 3/8 buried surface hoard was found about 12 inches below the snow surface. It was reactive in some snowpack tests. The 2/5 layer was also found in this area about 3 feet below the snow surface.