Avalanche Forecast

Issued: Feb 14th, 2017 11:16AM

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

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Wednesday will be a potentially dangerous day along the Cascade west slopes. Travel in avalanche terrain is not recommended along the Cascade west slopes on Wednesday.

Summary

Detailed Forecast

Strong southwest flow aloft will carry a very moist frontal system to the Northwest on Wednesday. This will cause stormy wet weather along the Cascade west slopes on Wednesday with rain and high snow levels. The most rain should be seen in the northwest zone at Mt Baker with several inches expected but pretty heavy rain should seen elsewhere along the Cascade west slopes. Some freezing rain may be seen near the Cascade Passes and at low elevations east of the crest. See the NWAC Mountain Weather Forecast for details.

Wednesday will be a potentially dangerous day along the Cascade west slopes. Natural or triggered large or very large loose wet and wet slab avalanches are likely or very likely on Wednesday depending on how much rain there is, how it percolates into the snowpack and if avalanches 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 actiivity.

But observations and tests for wet slab avalanches are more difficult since it is usually hard to know the effects of significant amounts of water percolating into the snowpack.

Travel in avalanche terrain is not recommended along the Cascade west slopes on Wednesday.

 

Snowpack Discussion

Weather and Snowpack

The aftermath of the last storm cycle 2/8-2/10 left a very strong rain crust with whatever amount of new snow received above, except for areas exposed to west winds which remained scoured to the firm and slick crust.  

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.

Recent Observations

North

NWAC pro-observer Lee Lazzara was in the Mt Baker backcountry Saturday and reported a favorable increasing resistance profile in the storm snow over the very strong rain crust. Observations were not made in terrain where wind slabs may have formed. 

Central

A report via the NWAC Observations page indicated many small loose wet avalanches on the south side of Mt Lichtenberg on Sunday.

The Stevens Pass pro-patrol reported no avalanche activity on Monday.

South

The Crystal Mountain pro-patrol on Monday reported some rollerballs on solar slopes at lower elevations with wind cooling the ridges.

NWAC observer Dallas Glass was at Paradise Sunday and confirmed the recent wind and storm slabs have settled and stabilized. By Sunday afternoon, strong sunshine and temperatures into the mid 40's triggered numerous rollerballs from many steep sun exposed terrain features, especially rock features. There was evidence of numerous wet slab avalanches that released several days ago during the heavy rain event with average crown depths around 2 feet. The underlying rain crust is now very hard and supportive, with an average of about 10 inches of recent snow over the crust in wind sheltered terrain.

Problems

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: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 1

Wet Slabs

An icon showing 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

Likely

Expected Size

1 - 1

Valid until: Feb 15th, 2017 11:16AM