Avalanche Forecast

Dangerous avalanche conditions will develop Tuesday as strong alpine winds build fresh Wind Slabs near and above treeline, transporting new and recent snowfall. You will be able to trigger Wind Slabs on steep slopes near or below ridgelines. Strong winds may build areas of Wind Slab further downslope than usual and transport snow onto a variety of aspects due to erratic loading patterns. Pay attention to stiff snow surfaces that produce cracking as a clear sign you should retreat to non wind-affected terrain. 

Rising snow levels on Tuesday will produce small Loose Wet avalanches below treeline. Watch for warning signs like new roller balls, pinwheels, and natural Loose Wet avalanches as temperatures rise and snow turns to rain below treeline. Even small Loose Wet avalanches may carry you into terrain with high consequences such as over cliffs or into gullies.

It has been more than two weeks since the last reported avalanche involving older weak layers. While many of these layers have not gone away, it is now difficult to trigger a Persistent Slab avalanche. If either snowfall or rainfall amounts are heavier than predicted through Tuesday night, they may become active again. Especially keep this in mind if traveling in terrain near the Cascade crest where a steep precipitation gradient will exist over short distances; much heavier rain and snow is forecast near and just east of the Cascade crest. Snowpack tests can provide useful information about buried weak layers, they are not a decision making tool. 

Mostly cloudy and cool conditions the past several days have preserved dry snow on many aspects, particularly in the northeast Cascades. Non-supportive crusts likely formed on southerly aspects.

Up to a foot of snow fell along the east slopes of the Cascades near Washington Pass from 3/21 through 3/24, with about half that amount accumulating in the East Central zone. During this period, Wind Slabs formed on lee slopes and cross-loaded features near and above treeline. The new snow fell on a variety of old snow surfaces. On sunny aspects, firm melt-freeze crusts were buried. In shaded locations, near surface facets and surface hoar were observed prior to the storm cycle. 

Persistent weak layers were involved in 3 avalanche fatalities over the past month. Many of these weak grain types have rounded and are no longer an issue. The remaining weak layers are generally inactive or dormant. Drastic changes to the snowpack, such as significant amounts of new snow or a major rain on snow event could make these layers a threat once again. Currently, the persistent weak layers that you may find include:

• Surface hoar and facets were buried on 3/8. This layer is typically found 18-24” (45-60 cm) below the snow surface on shaded aspects near and below treeline.
• Weak sugar-like facets (2/13 or 2/16) are 3-5 feet (90-150cm) below the snow surface. This is the most widespread persistent weak layer. It can be found just above a firm crust buried on 2/5. 
• 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 Saturday 3/23, professionals near Washington Pass reported a small skier triggered avalanche in the new snow on a steep east aspect at 6500 ft. The 3/8 buried surface hoar was reported as 1.5 feet below the snow surface.

Central

On Thursday 3/22, Mission Ridge Ski Patrol reported 4 inches of generally right-side-up storm snow by mid afternoon.