With a fair amount of water in the upper snowpack, wet snow avalanches will maintain dangerous avalanches conditions Thursday. Wet slab avalanches are hard to predict and powerful due to the high water content. Allow the snowpack to stabilize, avoiding steeper slopes and any avalanche terrain where even a small wet avalanche could have serious consequences.
Summary
Detailed Forecast
After a mild and wet Wednesday night, a slow cooling trend is expected on Thursday with light to moderate showers. With a fair amount of water in the upper snowpack, wet snow avalanches will maintain dangerous avalanches conditions Thursday. Wet slab avalanches are hard to predict and powerful due to the high water content, so extra caution is advised.
Loose wet snow avalanches may begin small but entrain deeper layers. Observations and tests for loose wet avalanches are more straightforward such as wet surface snow deeper than a few inches, rollerballs and natural loose wet avalanche activity.
Allow the snowpack to stabilize, avoiding steeper slopes and any avalanche terrain where even a small wet avalanche could have serious consequences.
Shallow storm or wind slab may start to form in the near and above treeline elevation bands by Thursday afternoon, but will not be listed among the primary avalanche problems for Thursday.
Snowpack Discussion
Weather and Snowpack
The 2/8 - 2/10 storm cycle left a strong rain or freezing rain crust with varying amounts of new snow received at the tail end of the cycle. Strong west winds on 2/10 exposed this firm and slick crust on windward aspects in many areas.
High pressure Saturday to Tuesday brought increasing sunshine and warm temperatures. Temperatures reached the 40's and 50's in many areas of the Olympics and Cascades by Monday and Tuesday. This caused a lot of snowpack settlement, some small loose wet avalanche activity and a decreasing avalanche danger.
Another atmospheric river impacted the PNW on Wednesday. Heavy rain at high snow levels fell along the west slopes of the Cascades with localized freezing rain along the lower slopes of the Cascade Passes.
Recent Observations
North
No observations on Wednesday.
Central
Alpental pro-patrol did not perform avalanche control Wednesday but reported a 1/2" freezing rain crust up to about mid-mountain with rain falling on the upper mountain.
South
No observations on Wednesday.
Problems
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: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wet Slabs
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
Expected Size
Valid until: Feb 16th, 2017 10:31AM
