Avalanche Forecast
Regions: Cascades - North West.
Forecast updated 8:05 AM to increase likelihood for Glide Avalanches. A strong front brings rapidly lowering snow levels and strong winds, building increasingly large slabs that you are more likely to trigger later in the day and at upper elevations. Look for evidence of wind-transported snow, including firm or textured snow or cracking of the snow surface. Mt. Baker has just received 7" of rain and water is running under the snowpack, so don't linger below steep, rock faces where the season's snowpack can detach suddenly.
Discussion
In the last 24 hours, Mt. Baker has added nearly 4.5†of water to the snowpack. Initially, 6†of snow fell Thursday evening, but steadily rising temperatures meant that the majority of the precipitation fell as rain, saturating the upper snowpack. Mt. Baker Pro Patrol reported loose wet avalanches running in the upper 6†snow that fell in the last 24 hours.
Tonight will bring more heavy rainfall with 6000-7000 ft snow levels in the evening lowering after midnight as a cold front approaches. The front should pass through the West North zone around 8 or 9 AM with rapidly lowering snow levels behind the front and a rapid transition to snow around this time. Strong winds in the morning should decrease throughout the day with decreasing light snow showers behind the front. Above treeline areas could see 8†or more of snow while near treeline, expect 2-8.â€
Several human triggered avalanches were reported in the Mt. Baker Backcountry on Thursday. Avalanches failed within the recent storm snow we received since Monday, primarily in northerly terrain above treeline. Some avalanches had impressive propagation and grew large (D2). Many natural avalanches triggered by cornice fall were reported as well and looked to have run during the wind event on Wednesday.Â
Recent natural avalanche (D2) triggered by cornice fall on a NW aspect at 5600ft on Table Mountain. 01/30/20. Photo: Zack McGill, Baker Mountain Guides
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
Wind Slabs
Saturday is a tricky day with rapidly building wind slabs that will be larger, more widespread, and more dangerous at higher elevations. Your danger depends upon how much new snow falls Saturday morning after the rain changes to snow and how strong the winds are once that snow arrives. Plan your outing with the rapidly changing conditions in mind, knowing that any exposed terrain may be wind-loaded by the afternoon and will be touchy to human trigger. Winds as strong as we expect may produce firmer slabs that propagate more widely than you expect, so even a shallow slab may be able to take you for a dangerous ride. Avoid any slopes steeper than 35 degrees where you find more than several inches of snow above a refreezing crust. Keep in mind that large, sagging cornices could fall and trigger a wind slab on the slopes below.
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
Updated 8:05 AM to increase likelihood of glide cracks to "possible". Glide cracks were active last weekend and may re-awaken on steep slopes over smooth bedrock where water drains under the snowpack. Watch for opening cracks and recent debris exposing steep bedrock slopes to indicate this surprising and unmanageable problem exists in your area. In general, avoid exposure to steep slopes near areas of running water in the snowpack. Loose wet avalanches may also be a hazard if you head out early in the day. If rain is actively falling on the snowpack, expect the potential for natural or human-triggered small avalanches in the upper 6” during the early morning hours.
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