Avalanche Forecast

Snow, wind, rain, and warm temperatures have combined to create dangerous avalanche conditions. Wind has drifted slabs on lee slopes above treeline. In some locations, these new slabs will overly lower density snow from earlier in the week. Visual clues such as blowing snow, fresh cornices, and cracks in the snow all indicate that you could trigger a Wind Slab avalanche. Observations have been limited from upper elevations and forecasters are less certain about conditions at these elevations.

Rain has set the stage for wet avalanche conditions. You may be able to trigger Loose Wet avalanches more easily near and above treeline than at lower elevations. The lower slopes are more rain-soaked. If water reaches buried crusts or softer layers of snow, Wet Slab avalanches could occur. Digging snow profiles can help you see the depth and extent of wet snow. That said, snowpack tests can be hard to interpret and Wet Slabs are hard to predict. They also can be very destructive. If you see slab avalanche activity in areas of wet snowpack, avoid traveling in avalanche terrain. There's a chance that large Glide avalanches could release naturally.  Use extra caution and avoid stopping near and below snow covered rock slabs where Glide avalanches could occur.

Expect a lull in rain on Friday with warming temperatures. The wind stacked fresh slabs on older drifted slabs above treeline. Rain has moved into higher elevation levels and soaked previously dry snow laid down early this week. The April 1st-2nd storm deposited a relatively even blanket of 1.5 feet of snow across the Cascades West and Passes zones. Aside from the Mount Baker area and the West Slopes North zone, few avalanches were reported with the storm. Interfaces of concern were limited to reports of isolated graupel on a crust at the 4/1 interface. In most locations, this new snow fell on a firm melt-freeze crust up to 5,500ft. On Tuesday, observers easily triggered large, fresh cornices on test slopes. Meanwhile Wind Slab avalanches were harder to trigger. 

Observers have been tracking persistent weak layers deeper in the snowpack. The exact distribution of all of these layers is not well known. Where they have been found, there is good evidence that they are generally difficult to trigger.

Crystal: A weak interface buried on 3/22 can be found 2-3 feet (60-90cm) below the snow surface. On sunny aspects, a thin layer of weak sugary facets can be found just above a firm melt-freeze crust. On shaded slopes buried surface hoar has been reported.

Below the top 2-3 feet (60-90cm), the snowpack is generally well bonded and significant layers of concern. The much older 2/8 melt-freeze layer can still be found over 6 feet (200cm) deep in the snowpack. While this layer isn't listed in our current avalanche problem set, it may reawaken if enough liquid water reaches it during the coming rain storms.

Observations

Central

NWAC avalanche forecaster Josh Hirshberg was at Stevens Pass Monday and Tuesday. Josh reported 16 to 18 inches (40-45cm) of new snow in sheltered locations. Near ridgeline, winds  transported snow, forming drifts up to 22 inches (55cm) deep. No new avalanches were observed.

NWAC avalanche forecaster Dallas Glass traveled in the Snoqualmie Pass area Tuesday. Dallas found 18-24 inches (45-60cm) of settled storm snow, generally well bonded to the old 4/1 crust. Several natural and human triggered loose dry avalanches were observed. 

South

NWAC professional observer Jeremy Allyn traveled in the Crystal backcountry Monday. Jeremy found wind transported snow above 6000 feet. The new snow was moderately bonded to the old snow surface with the bond strengthening during the day. As the sun came out, sunny aspect quickly became moist to wet and produced rollerballs.