Avalanche Forecast

A period of moderate to heavy rain Saturday morning transitioned to snow by late Saturday afternoon following a strong frontal passage. Very strong winds and further snowfall in moderate showers will continue Saturday night and Sunday.

Continued winter-like stormy weather will create dangerous avalanche conditions Sunday at most mid and upper elevation terrain. 

Wind Slabs will build on lee slopes and a variety of cross loaded terrain features, possibly lower on slopes than typical, due to very strong winds where you could trigger a Slab avalanche. Use visual clues such as blowing snow, fresh Cornices, and cracks in the snow all indicating that you could trigger a Wind Slab avalanche. 

While the bonding of new snow to the old wet snow surface should be favorable, unstable Storm Slabs will build on a variety of steep terrain, especially in those areas receiving the greatest new snow amounts. Watch for deeper stiffened slabs developing Sunday on a variety of aspects.

Fresh Cornices are likely to build along ridges, so give Cornices a wide berth if traveling along ridgelines as they often break back further than expected. Be aware of overhead hazard if traveling on slopes with Cornices above as they may fail naturally or be human-triggered. 

A vigorous storm Saturday caused periods of heavy rain and warm temperatures early Saturday that transitioned to snow or wet heavy snow by Saturday afternoon with shallow new snow beginning to accumulate by Saturday afternoon. The old rain soaked snowpack has begun to refreeze and form a crust under continued cooling. Cooler temperatures in the NE Washington Cascades limited the rain to lower elevations.

Up to 6 inches of snow fell earlier in the week. Strong W-NW winds redistributed recent snow onto lee slopes above treeline forming shallow wind slabs. 

Older layers of weak snow can be found in the snowpack. We have limited information about the distribution and reactivity of these layers leading to a higher level of uncertainty. If you have any information or observations on layers within the snowpack please consider submitting them to NWAC via our public observations page. The exact weak layer and depth depends on your location. Common weak layers are:

• 3/25: Buried surface hoar layer found on shaded aspects near and above treeline.
• 3/22: Buried surface hoar layer found on shaded aspects near and above treeline.
• 2/13 Facets above a firm and thick melt-freeze crust can be found in many locations near and above treeline. This layer is thought to be dormant at this time but may re-awaken with a substantial weather input.

Rainfall and continued above freezing temperatures Friday night and Saturday morning may allow Wet Slabs to fail at these interfaces. Peristent Slabs may be reintroduced when we receive more snowpack information following this storm cycle. 

Observations

North

On 3/23, professionals near Washington Pass reported the 3/8 buried surface hoar was reported as 1.5 feet (45cm) below the snow surface.

Central

On Friday 4/6, professional observer Matt Primomo traveled up the Icicle to above Colchuck Lake. Matt found a moist and well settled snowpack below 5800' with no persistent weak layers. The 2/8 crust was 1 m down.  At 6700' on a NNE aspect, Matt found preserved stellars 14 in (35 cm) down and showing a likelihood to propagate in snowpack tests. Dry snow was found at this elevation below the top 8 " (20 cm). Higher in the terrain, recent wind slab avalanches likely released on this layer. Matt also observed natural loose wet avalanches and one wet slab avalanche above treeline on a SE aspect.  

On Saturday 3/31, an observer reported a large slab avalanche that likely failed on a persistent weak layer 4-5 feet below the surface in the Enchantment Mountians

On Friday 3/30, Matt Promomo was on Dirtyface Mountain where he found two buried surface hoar layers (3/22) on shaded aspects at variable depths within the two feet of the snowpack. Test results indicated the potential for propagation on both weak layers. Snow pits indicate a weakening 2/8 crust.