Avalanche Forecast
Regions: Cascades - North West.
The potential for very large and destructive natural avalanches will lower Tuesday, but will still require you to avoid terrain connected to larger avalanche paths. Strong winds above treeline will continue to build on already deep wind slabs. Powerful wet slab avalanches may still occur in isolated areas below treeline. Be aware of the overhead hazard and travel cautiously Tuesday.
Detailed Forecast
The potential for very large and destructive natural avalanches will be lower Tuesday, but will still require you to avoid terrain connected to larger avalanche paths. Be aware of the overhead hazard and travel cautiously Tuesday.Â
Much cooler snow levels combined with snow showers will help the wet upper snowpack begin to refreeze near and below treeline. Powerful wet slab avalanches may still occur in isolated areas below treeline. Wet slab avalanches are difficult to predict and may occur well after the peak warming/rainfall has ended.Â
Be aware that the snowline likely did not reach into the above treeline for a sustained period of time Sunday or Sunday night, with the expectation that significant storm snow accumulated above treeline. Strong winds forecast Monday night and Tuesday above treeline will continue to build on already deep wind slabs. Look for shallower wind slabs to develop near and even below treeline Tuesday.Â
In areas receiving more more intense snowfall rates, fresh storm slabs will build and may become touchy to trigger. Constantly evaluate the sensitivity of the snow, checking small test slopes.
Snowpack Discussion
The Mt Baker area received 13 feet of snow in the 10 days ending Sunday 1/28, a massive amount even by Mt Baker standards! Warming temperatures and rain arrived early Sunday and continued through the day on Monday, with over 5 inches of rain falling through early Monday afternoon below 4500 feet over the preceding 36 hours. Significant snowpack settlement has occurred over this period. Snow levels dipped to 5000 feet Monday morning. Significant storm snow, likely 2-3 feet, has accumulated above 5000-6000 feet since Monday morning.  Â
Above treeline, deep storm snow sits over a strong crust layer.
Winds over the past few days have redistributed snow creating deep wind slabs on lee slopes near and above treeline.
Numerous natural avalanche cycles have occurred over the stormy period.
Observations
On Monday, Mt. Baker pro-patrol observed debris from several large natural avalanches that had run off of Shuskan Arm. Avalanche control work with large explosives resulted in several large avalanches with 2-3' crowns in area.Â
NWAC professional observer Lee Lazzara was in the Mt Baker backcountry Saturday. Lee report several large natural avalanches in the backcountry area. Poor visibility limited detailed descriptions or more extensive observations. Observations found strong surface snow over soft weak storm snow from Friday. Shooting cracks and small slope tests all pointed to storm and wind slabs being easy to trigger. Even basic travel in the deep heavy snow was difficult.
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: Very Likely
Expected Size: 1 - 2
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
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.
Elevations: Below Treeline.
Likelihood: Unlikely
Expected Size: 1 - 2