Avalanche Forecast
Regions: Cascades - North West.
Dangerous avalanche conditions will persist in the Mt. Baker area Tuesday as we transition to a cooler snowier pattern. You can still encounter large and destructive Wet Snow avalanches at lower elevations, including large Glide avalanches. Avoid stopping near and below snow covered rock slabs where Glide avalanches could occur. You can trigger fresh Wind Slabs near and above treeline in the afternoon.
Detailed Forecast
On Tuesday, a frontal system will bring a rapid cool down with new snowfall accumulating above 4500-5000 ft by the afternoon. You may still trigger Loose Wet avalanches or they may be triggered by additional rainfall Tuesday morning. Watch for signs of wet snow conditions such as sluffing, roller-balling and any natural Loose Wet avalanches as signs of an increasing hazard. Loose Wet avalanches still have the ability to become large in areas where they gouge down to deeper layers of moist or wet snow.
In the Mt. Baker area, be cognizant and avoid exposure below unsupported slopes as the potential for Glide Avalanches will increase during prolonged rainfall and warm temperatures at lower elevations. Use extra caution and avoid stopping near and below snow covered rock slabs where Glide avalanches could occur.
New Wind Slabs will form on lee slopes near and above treeline by the afternoon. Use visual clues such as fresh cornices, wind drifted pillows and cracks in the snow all indicating that you could trigger a Wind Slab avalanche. Strong winds will likely make for erratic loading patterns, suspect Wind Slabs may be present on all aspects.Â
Large fresh cornices will still be fragile due to recent warm temperatures and initial rainfall Tuesday morning. Give cornices a large margin of safety and avoid travel on slopes below, as cornice failures may trigger large avalanches on slopes below.
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Snowpack Discussion
Monday was warm with filtered sunshine. The dry weather followed the strong weekend storm which initially pushed rain into the near and above treeline elevations bands early Saturday. Cooling and significant new storm snow followed through Sunday afternoon with 1 to 2+ ft of snow above 4000-4500 feet. There was a significant snowfall gradient with elevation with this spring storm. Wet snow avalanches were seen earlier in the storm and continued at lower elevations through the weekend. New Wind and Storm Slabs developed at higher elevations later in the weekend with fresh cornices developing along ridgelines.  Â
Moist or wet snow can be found in the upper snowpack. The 4/1 firm crust may still exist in some areas, it has most recently been identified in the Crystal area 1.5-2 ft down.Â
Out of the weak layers that we've tracked through the season, the 2/8 crust can still be identified in many areas 5-7 feet below the surface. This interface was associated with the 2/13 facets. Though it's unlikely, if significant water pools on the crust, it could result in very large and dangerous Wet Slabs.
Observations
North
On Friday, NWAC observer Jeremy Allyn traveled in the Bagley Lakes area. He reported many Wet Loose and Slab avalanches on north, east, and south aspects around 5,000 ft. Some were big enough to bury a person. He also found very wet snow in the upper 2 ft of the snowpack and challenging, wet travel conditions.
Central
Stevens Pass DOT and Stevens Pass Pro-patrol reported large and destructive avalanches during control work that released as soft slabs with explosives and quickly entrained wet snow at lower elevations on Monday. In a section of the ski area with minimal skier traffic on the east end of Cowboy Ridge, this explosive triggered slide (SS-AB-D2.5-R3-O) on a north aspect produced 4-5 ft of debris as it entrained old saturated snow below. Â
Pro-observer Matt Primomo observed recent natural wet snow and storm snow avalanches in the Stevens Pass backcountry over the weekend, including this recent Litchenberg Wet Slab Avalanche on a SE aspect at 5200'.Â
Pro patrol at Alpental Sunday reported about 1 ft of new storm snow that was sensitive to ski triggering, releasing soft slab avalanches of 8-12" and running long distances, entraining all the recent snow, running on the old wet snow surface. At lower elevations the new snow was easily releasing as Wet Loose avalanches by skis.Â
South
NWAC professional observer Jeremy Allyn traveled in the Crystal backcountry Monday 4/9. Through mid-day, Jeremy found poor travel conditions as the surface crust quickly broke down with moist or wet snow in the upper snowpack. Recent large Wet Loose and one Wind Slab avalanche from the weekend were observed in surrounding terrain.Â
Avalanche Problems
Wind Slabs
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Glide Cracks
A release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often preceded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
Predicting the release of Glide avalanches is very challenging. Because Glide avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide avalanches.
This Glide avalanche broke to the ground on a smooth, grassy slope. From all the mud on the bed surface, water pooling at the base of the snowpack likely caused the failure.
Glide avalanches occur when water lubricates the interface between the snowpack and the ground. These avalanches are difficult to predict and best managed by avoiding terrain below glide cracks.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 2
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.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1