Avalanche Forecast

Dangerous avalanche conditions will persist at higher elevations Wednesday. Allow recent Wind Slabs and new snow instabilities one more day to settle near and especially above treeline by choosing more conservative terrain options. New snowfall totals increase quickly with elevation, and so does the potential for larger avalanches.  

You will be able to trigger Wind Slabs on steep slopes near or below ridgelines at higher elevations. Watch for clues like variable snow height, drifts, cornices, and stiff snow that produces cracking. These are all indicators that you could trigger a Wind Slab. You can avoid triggering these avalanches by steering around steep roll-overs, unsupported features, and obvious start zones where you suspect Wind Slabs.

Although not listed, you may also be able to trigger lingering Storm Slabs on steep slopes near treeline in less wind affected terrain. Watch for cracking and stiff snow over softer snow near the surface. 

Generally small Loose Wet avalanches are possible on steep sunny slopes near and below treeline, especially during prolonged sunbreaks. Watch for warning signs like new roller balls, pinwheels, and natural Loose Wet avalanches that indicate increasing hazard. Even small Loose Wet avalanches may carry you into terrain with high consequences such as over cliffs or into gullies. In isolated areas below treeline, Loose Wet avalanches may gouge down into deeper layers of wet snow and become large. Cooler temperatures Tuesday night and Wednesday should help surface crusts form on more northerly aspects and shaded terrain. 

It has been more than two weeks since the last reported avalanche involving older weak layers. Deep Persistent Slab avalanches are now very unlikely. The weak snowpack structure could be become a problem later in the spring.

A rising snowline Tuesday led to a large snowfall gradient with elevation. At Stevens and Snoqualmie Pass rainfall limited accumulation at Pass level. For higher elevations at Stevens and Snoqualmie and also at Paradise and Mt. Baker, 12-18 inches of snow accumulated Monday through Tuesday afternoon. Less snowfall accumulated in the Crystal Mt area. Moderate to strong westerly winds were observed near and below ridgelines. Elevations that received rain should begin to form surface crusts late Tuesday night and Wednesday as colder air arrives.   

Prior to this storm cycle, about 1 ft of new snow fell near Crystal, Paradise, and Stevens and Snoqualmie Passes. Observers reported a range of avalanche activity over the weekend including triggered avalanches in wind loaded terrain near Mt Baker and the Crystal backcountry and numerous small natural slab avalanches in the upper storm snow near Snoqualmie Pass.

Snow from the past week sits on the 3/22 interface. On sunny slopes you will find a crust, and in some locations (especially near Crystal Mountain) you may find a layer of small facets or surface hoar at this interface. Below this interface, the snowpack is generally well-rounded, strong, and lacking interfaces of concern.

An old, thin layer of sugary facets (2/13) can still be found in some locations just above a very firm and wide spread crust (2/8). The overall depth (1.5-2 meters) and significant rounding (melt-freeze cycles in some locations) has allowed this structure to drop off the official list of avalanche problems. NWAC professionals will continue to track this weak layer as it could be a problematic later in the spring.

Observations

North

On Sunday, NWAC Observer Lee Lazzara traveled near Hidden Lake. Lee found about 1 foot of recent snow topped with widespread surface hoar up to treeline.

Central

On Tuesday, Stevens Pass Pro-Patrol reported gusty west winds redistributing snow onto all aspects. Rain at Pass level in the afternoon caused small Wet Loose avalanches. A skier triggered avalanche was reported outside the ski area near Gemini Pass. This slab avalanche may have released down to the 3/22 crust. 

On Monday, NWAC Forecaster Josh Hirshberg traveled in the Stevens Pass backcountry. Josh reported 4 inches (10-15cm) of new snow by mid-day. Over a foot of snow sat on a crust formed by rain last week. Snow from the past week was generally well bonded below treeline. Josh observed minor cracking in sheltered areas, but no new avalanches.

South

On Monday, NWAC Observer Jeremy Allyn investigated recent avalanches on SE and NW aspects around 6400 ft in the Crystal backcountry. Jeremy reported that both avalanches ran on thin weak layers just over a foot below the surface. A nearby profile on a west aspect produced propagating test results.