Avalanche Forecast
Regions: Cascades - North West.
Unpredictable glide avalanches remain a gradually decreasing concern as water continues to drain under the snowpack. Use terrain management to distance yourself from drainage depressions and steeper slopes where you suspect water might be flowing. Prepare for slide-for-life conditions with a stout crust developing on all aspects and at all elevations below 7000 ft.
Discussion
Mt. Baker picked up 9.68†of water over the last 48 hours and essentially all of that came as rain (aside from an initial 6†of snow). Mt. Baker Pro Patrol reported several large natural wet avalanches that released on steep slopes. On Chicken Ridge, a north-facing slope at 4700 ft, water was pouring out onto the exposed slabs after the climax release. Strong winds gusting extreme (up to 110 mph) were recorded at the Pan Dome weather station Friday night and through much of the day on Saturday. Although a frontal passage brought cooling temperatures and formed a crust on the surface, water continued to rapidly drain the snowpack throughout the day.
Snowpack Discussion
Looking Back at January
As we turn the corner from January to February, this is a good time to look back at the last month’s snow, weather, and avalanche conditions. January was notable for continuous storms and elevated, yet quickly resolving avalanche danger. In most parts of the region, the snowpack grew significantly. Snow depths went from far below average at the New Year to near normal by the end of the month. While numbers are still being compiled, January 2020 could rank high for total precipitation amounts in some locations. As we move forward, there are currently few layers of concern in the existing snowpack.
Snotel weather stations report well above average precipitation amounts for the month of January. Source: www.nrcs.usda.gov
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Weather
January was marked by an onslaught of storms with very few breaks in precipitation lasting 24, or even 12 hours. Most notable was the sheer amount of precipitation that these storms delivered. Most NRCS Snotel weather stations are reporting at least 125% of average precipitation amounts for January, with many over 200% of average. Not all of this fell as snow. Snow levels and temperatures were less consistent than the overall stormy weather. On the heels of a warm December, the first week of the New Year followed suit. From about January 8th through the 19th a cold period had its grasp on the state, bringing snow to the lowlands and copious amounts of light, champagne powder to the mountains. The last third of the month saw continued storms. Temperatures moderated and warm air brought occasional rain to middle and even upper elevations.Â
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A small skier triggered avalanche (D1) within new snow on a NE aspect at 5600ft on Mt. Herman. 01/28/20 Photo: Zack McGill
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Snow and Avalanche Danger
After a meager start to the winter, the snowpack grew exponentially in January. In fact, the storms were so intense in the middle of the month that they challenged the accuracy of remote weather stations. Snow blocked precipitation gages and knocked out cellular towers and phone lines used to transmit data. Currently, snow depths from reporting sites are near average.
While the storms often brought rapid spikes in avalanche danger, the hazard was quick to taper off. Throughout the month, there were 12 days when NWAC issued High Danger in one or more zones and 11 days when there was at least some Low Danger in forecasts. It’s notable that there were no days with all Low Danger in any forecast zone. In addition to the snowpack growth, a positive side to the storms was that weak layers had little time to form. In general, any facets or surface hoar that formed were very short-lived weak layers. Most avalanche problems involved new snow, wind or wet snow. There are still some areas of shallow, weak snowpack in typical places like the Wenatchee Mountains and the most eastern extent of the Cascade Mountains. Aside from that, the snowpack layering in most zones is marked by a few lingering storm interfaces in the upper snowpack and intermittent crusts from rain events. If you dig in the snowpack around the region, the most prominent crusts you’ll find formed from rain events roughly around January 1-3rd, 7th, MLK weekend, 23-25th, and the 31st.
The winter snowpack is now well established for recreating and traveling through the mountains. Much more so than it was a month ago. Looking ahead, there’s a good chance this stormy pattern will continue at least into early February. We’ll keep monitoring how the snowpack continues to change near the surface with each weather event. You can check the daily Avalanche and Mountain Weather forecasts for the most up to date information.Â
Avalanche Problems
Glide Cracks
While it feels like a normal, chilly winter's day, water lurks in and under the snowpack. The amount of water the West North zone has recently received requires multiple days to drain the snowpack. The threat of glide avalanches is decreasing, but with 123” of total snow depth a climax avalanche failure would result in low odds of survival. Watch for cracks opening in the slopes - precursors to potential glide avalanches. Listen for the sound of running water. Then, mitigate your exposure to steep slopes lubricated by running water from below.
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.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 2