Avalanche Forecast
Regions: Snoqualmie Pass.
Warm, wet, and windy conditions should create very dangerous avalanche conditions Wednesday. Avoid traveling in areas where avalanches can start, run, and stop. Natural avalanches will be most likely during periods of intense precipitation, blowing snow, and rapidly warming temperatures.
Snowpack Discussion
January 30th, 2020Â (The regional synopsis is updated every Thursday @ 6 pm)
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.Â
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. For the month of January, the Mt. Baker, Snoqualmie Pass, Paradise, and Mt. Hood Meadows weather stations measured an astounding 42â€, 33â€, 32†and 28†of water (both rain and snow) with 1 day still left in the month. If you do some quick math, those 4 stations average near or above an inch of water a day! Â
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 region, 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.
Looking Forward
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
Storm Slabs
Anticipate large natural and human triggered avalanches at mid and upper elevations. If you travel out of the deep dark forest, stay away from areas where avalanches start, run, and stop. All the pieces are in place for a natural storm slab cycle; weak snow surfaces, heavy snowfall, warming temperatures, and strong winds. The question is more about when will the avalanches occur rather than if. Look for avalanche activity to peak during periods of snow changing to rain, heavy precipitation, and blowing snow.
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: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 1 - 1
Loose Wet
As temperatures warm snow will transition to rain. When this happens, you will probably see loose wet avalanches. Steer away from steep slopes and be aware of terrain above you. Wet avalanches can be tricky. You could see wet slab avalanches in areas where enough new snow accumulates over the weak snow surface prior to changing to rain. As snow levels continue to rise to higher elevations wet avalanches could become larger and travel further.
Two other avalanche concerns should be on your mind. Glide avalanches could occur as more rain lubricates the ground below the snowpack. Additionally, cornices could fail naturally. Be leery of traveling on or below either of these timebombs.
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: Likely
Expected Size: 1 - 1