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Archived

Avalanche Forecast

Mar 18th, 2019–Mar 19th, 2019
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: Snoqualmie Pass.

The snowpack in the Snoqualmie Pass area is struggling to adjust to these warm temperatures. Be patient and let the mountains make this transition. Stay away from steep open slopes and a don’t linger in locations where avalanches can run and stop.

Discussion

Snow and Avalanche Discussion

This week’s warm weather is a tough transition for the mountain snowpack. We spent nearly six weeks with below average temperatures. Now, on Monday, temperatures in the lowlands are hitting record highs. That’s a big change. When it comes to the snowpack, big changes often mean big problems. On Tuesday we’ll be heading into our 3rd straight day of above freezing temperatures at Snoqualmie Pass. While a cool easterly wind may delay thawing of the snow surface, it won’t take much time for the sun and warm temperatures to create wet snow.

On Monday morning, NWAC staff observed several avalanches that occurred over the weekend. The presence of numerous overlapping debris pile should be all the reminder you need, that this avalanche cycle is ongoing. Of note were a few isolated wet slab avalanches these were all relatively small and were triggered by loose wet avalanches from above.

During spring periods like this, plan for changing conditions. Slopes you travel on in the morning can be very different by mid-day. On Monday, slopes went from frozen to wet in the matter of 30 minutes on sun-exposed slopes. Be leery of traveling near or under cornices. They are experiencing the stress of this heat too, and may fail without warning.

Snowpack Discussion

New Regional Synopsis Coming Soon

Avalanche Problems

Loose Wet

Each successive day of warm weather adds more water to the snowpack. Now we are seeing loose wet avalanches entrain more wet snow, grow larger, and run farther. A poor overnight refreeze, means it won’t take long Tuesday for wet snow to develop on the surface. Unless it’s frozen, it should be suspect. Stay away from steep open slopes with wet surface snow. We are seeing loose wet avalanches at higher elevations and on shaded aspects as this warm weather continues. 

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: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 1

Wet Slabs

The snowpack in the Snoqualmie Pass area still contains several cold snow layers. As more and more water moves through the snowpack, we may see increasing wet slab activity. The problem is, wet slabs are extremely hard to predict, but honestly that doesn’t matter. This isn’t an avalanche problem you want to try to mess with. Be suspicious of any open slope greater than 30 degrees and don’t linger in large avalanche terrain.

Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.

 

Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty

 

A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.

Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 1