Avalanche Forecast

Issued: Jan 22nd, 2020 10:00AM

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

Northwest Avalanche Center NWAC, Northwest Avalanche Center

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Expect very dangerous avalanche conditions to develop in locations receiving the greatest precipitation Thursday and during periods of heavy rainfall. Give any avalanche slope a wide berth, including where avalanches could run and stop.

Summary

Discussion

The West South zone will experience an array of conditions Thursday based on location and precipitation amounts. Areas like Paradise, Mt St Helens, and Mt Adams should see the highest rainfall and avalanche dangers. However, even in areas with less precipitation, this should be a very warm, wet, and windy day. Uncertainty exists around the details of this forecast, but we expect the rain on snow to develop very dangerous avalanche conditions in the West South zone during this time period. Areas where significant recent dry snow rests on the MLK crust, which subsequently receive rain, could experience the largest and easiest to trigger avalanches. This crust is the most prominent above about 5500' in the West South zone. 

Snowpack Discussion

New Regional Synopsis coming soon. We update the Regional Synopsis every Thursday at 6 pm.

Problems

Wet Slabs

An icon showing Wet Slabs

Wet slabs are incredibly difficult to predict and asses. Their unpredictability and very large destructive nature cause them to deserve our respect. Steer around any steep open slope, and stay away from areas where very large avalanches could run and stop. Don’t forget about the terrain above you. Natural avalanches could travel into the below treeline band in some areas. We’re particularly concerned about wet slabs during this rain on snow event due to the dry and structured nature of the upper snowpack over the MLK crust. In some areas, more than 2-3’ of snow sits above the crust. Loose wet avalanches often occur in the same elevation bands as wet slabs and could act as triggers for slab activity.

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: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 2

Loose Wet

An icon showing Loose Wet

At lower elevations, the snow over the MLK crust is shallower and moist. In these areas, we’re more concerned with loose wet avalanches. New rollerballs and other avalanche debris should clue you in that loose wet slides are likely. With the recent new snow, loose wet avalanches could grow large enough to bury and kill you.

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.

Elevations: Treeline, Below Treeline.

Likelihood

Very Likely

Expected Size

1 - 1

Valid until: Jan 23rd, 2020 10:00AM