Avalanche Forecast

Issued: Mar 6th, 2016 10:12AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Storm Slabs and Loose Wet.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Be wary of unstable layers created during periods of rapid accumulation Monday that would make shallow wind or storm slabs more likely to trigger. Overall the potential for loose wet avalanches will decrease Monday and be confined to the lower elevations of the below treeline band and to steeper solar aspects that receive sunbreaks. 

Summary

Detailed Forecast

Light to locally moderate new snow received through Monday afternoon should accumulate at relatively cool and stable snow levels. 

Be wary of unstable layers created during periods of rapid accumulation Monday that would make shallow wind or storm slabs more likely to trigger. Overall the potential for loose wet avalanches will decrease Monday and be confined to the lower elevations of the below treeline band and to steeper solar aspects that receive sunbreaks. Wind slabs are possible at higher elevations but will not be specially listed following this storm cycle. 

Cornices formed over the last week may still be weak from the recent mild weather so be aware of the overhead hazard and give cornices a wide berth while traveling along ridgelines. 

Non-avalanche hazard: Despite our seasonally, healthy snowpack, many creeks are open and difficult to cross due to the periodic warm temperatures and rain events.

Snowpack Discussion

Weather and Snowpack

The last week has been wet and relatively mild with a series of active fronts transiting the region resulting in fluctuating freezing levels and periods of very strong winds. The heaviest snowfall and precipitation occurred late Sunday 2/28 and Tuesday 3/1. The latter half of the week including the weekend has featured more rain than snow at NWAC sites along the west slopes. For perspective, the averaged freezing level measured in March thus far has been 5700 ft at Forks (Washington Coast) and 6400 ft at Spokane. When the average freezing levels are warmer on the east side of the Cascades versus the west side, that bodes poorly for the influence of cool easterly flow and freezing levels along the west slopes including the Passes become more aligned with the average Forks freezing level. 

Mid and lower elevations have seen natural, loose-wet avalanches most days as radiation increases in early March or during rain events. Particularly in the Mt. Baker area, unsupported slabs continue to sporadically release during extended stretches of mild temperatures and rainfall resulting in glide avalanches in very specific terrain features like steep rock faces.

The mid and lower snow pack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

From Wednesday through Friday of last week periods of sunshine along with significant daytime warming caused numerous natural loose wet avalanches on steep aspects, mostly below about 4500-5000 feet, seen in the Alpental Valley and the Mt Baker backcountry.

Locally heavy rain at the Mt. Baker area led to sensitive loose wet ski cuts by the Mt. Baker pro-patrol early Saturday morning. A natural loose wet cycle was observed in the Bagley Lakes area and one glide avalanche in unsupported terrain released nearby. Also in the Baker area, another glide avalanche occurred Saturday night off Shuskan arm entraining moist surface snow and becoming very large while running to the valley bottom.

Problems

Storm Slabs

An icon showing Storm Slabs

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

 

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 1

Loose Wet

An icon showing Loose Wet

Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

 

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

 

Several loose wet avalanches, and lots of pinwheels and roller balls.

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

Aspects: South East, South, South West.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 1

Valid until: Mar 7th, 2016 10:12AM