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Avalanche Forecast

Archived

Jan 29th, 2018–Jan 30th, 2018

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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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. 

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. 

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. 

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.   

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. 

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.

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.

Wet Slabs

Wet Slab avalanches are the 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 Slabs can be very unpredictable and destructive.