Avalanche Forecast

The Avalanche Danger will increase to Considerable by Monday afternoon due to a robust round of new snow and wind. You can trigger Wind Slab avalanches at upper elevations on steep slopes near ridge tops or in cross-loaded terrain features. 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.

You may be able to trigger small Storm Slabs on steep slopes near and below treeline where storm totals exceed 6 inches. Watch for areas where the storm snow easily slides on the old snow surface. Use quick tests and small test slopes to check for a poor bond of the new snow.

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

The main concern for avalanches over the next couple days will lie with incoming snow and wind. Expect just enough new snow by Monday afternoon to see heightened conditions. Snow (and rain at low elevations) will continue into the week. The new snow could fall on surface hoar, light crusts, or settle powder depending on location. This past weekend, about 1 foot (35cm) of new snow fell near Mt Baker and Stevens and Snoqualmie Passes. Observers reported a range of conditions including triggered avalanches in wind loaded terrain near Mt Baker and small natural slab avalanches in the upper storm snow near Snoqualmie Pass. These storm instabilities should have run their course by Monday.

Last weekends storm fell on crusts at low elevations and sunny slopes. Many slopes hold a series of thin crusts in the upper snowpack. You may find some buried softer layers on shaded slopes, but these have generally not been problematic. Below the top 2 feet (60cm) 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

Mt Baker and North West Cascades

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.

Lee traveled in the Mt Baker backcountry Friday and reported 1’ (30cm) of new snow over a growing melt freeze crust. He observed several small skier triggered wind slab avalanche near ridges and on cross-loaded terrain.

Stevens Pass

On Thursday NWAC forecaster Josh Hirshberg traveled in the Stevens Pass backcountry. Josh reported 4-6 inches (10-15cm) of new snow in sheltered locations. Evidence of recent rain was observed up to around 5000 feet. Moderate winds at ridgeline were transporting the new snow forming small drifts.

Snoqualmie Pass

NWAC staff were in the Snoqualmie Pass backcountry Saturday. They found 12" (35cm) of low density new snow. Wind affected snow was only observed in isolated features near ridge tops. Good visibility in the afternoon allowed them to see across the area. Numerous small slab avalanches were reported below treeline in steep terrain.