Avalanche Forecast

Persistent Slabs avalanches are difficult to manage. 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. Persistent Slab avalanches have been the cause of fatalities or serious injuries every weekend for the past 4 weeks in the Cascades.

Until southerly slopes get softened by the sun they will remain hard and slick. If you travel on these slopes while they are still firm it may be difficult to stop a fall. Avoid falling into glide cracks and stay out from under large cornices. You may see lingering areas of snow that was drifted last week. Winds Slab avalanches are now difficult to trigger.

Expect cool temperatures and a mix of sun and clouds for Monday. If the sun comes out for long enough, it could soften the surface of sun-exposed slopes. While there may be a few rollerballs in areas that received a couple inches of recent snow, Loose Wet Avalanches should not be a problem. A dusting of light snow on Saturday and Sunday followed a warm, sunny stretch at the end of the work-week. 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. The distribution of this layer is not widespread. 
• 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 Thursday, North Cascades Heli reported 6 inches of new snow over a variety of old snow surfaces. Where found, the 3/8 buried surface hoar layer continues to be reactive in snowpack tests. This layer is 10-15 inches below the snow surface in this location. The 2/5 firm crust was observed down about 2.5-3 feet below.

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.