Avalanche Forecast
Regions: Cascades - East.
You may see some small loose wet avalanches on sunny slopes as the day warms. Even at low danger you should minimize your exposure to avalanche terrain, especially if venturing into bigger avalanche paths and committing routes. Don't linger under or near hazards such as large cornices, as they could fall with warming.
Discussion
On Wednesday an observer in the Icicle drainage reported a few small wet loose avalanches on southerly aspects and surface hoar and facets on the surface of most other slopes. On Tuesday, an observer in the Chiwaukum Mountains on a north aspect at 6400ft reported some lingering interfaces in the top 4 feet of the snowpack going as far back as February 1st, but none that showed test results conclusively pointing to a potential for triggering avalanches. Both observers reported generally soft and dry surfaces on northerly and shaded slopes. In the Chiwaukums, wind effects from the weekend were variable including some older drifts at ridges and scoured slopes even below treeline. Cornices were large and overhung above 6,000ft but were difficult to trigger. Ski cuts and dropped cornices produced only small loose dry avalanches on leeward slopes. Old avalanches were reported as evidence of the avalanche cycles from February 7th and 16th.
On Sunday, there was a multiple burial incident in the nearby Stevens Pass zone which involved a layer of small facets above a crust 2-3 feet below the surface on a southeast aspect. If you observe signs of instability such as shooting cracks or collapses on sunny slopes, especially southeast, avoid slopes over 30 degrees.
Snowpack Discussion
February 13, 2020 (The regional synopsis is updated every Thursday @ 6 pm)
Heart of Winter
The action has been non-stop so far in 2020 with several widespread natural avalanche cycles and a few recent close calls. The active weather pattern has kept us all on our toes, especially January’s barrage of storms bringing seemingly endless precipitation and dramatic snowpack growth. Ongoing snow, wind, and rain continued into February, and a not-so-ordinary atmospheric river event recently left its mark on the region. The second week of February brought the first stretch of high pressure in weeks, allowing the snowpack to gain strength and the avalanche danger to ease between storms. Now, in the heart of winter, we have a deep and healthy snowpack with snow depths throughout the Cascades and Olympics near 100% of normal. Looking ahead, each day brings new changes to the upper snowpack, and a dynamic pattern with direct action events (storm-driven avalanche danger) will likely be par for the course.
Atmospheric River AftermathÂ
Model simulation for February 5-6th, 2020 showing an Atmospheric River (AR) with a less than common northwest-southeast orientation as it impacts the region. This orientation allowed for strong westerly winds and more favorable upslope flow than a more typical AR approaching from the southwest. Image courtesy of the Center for Western Weather and Water Extremes, UC San Diego. (Link)
An atmospheric river impacted the region on February 5th-8th, causing a string of notable events. This storm favored the Central Cascades and Stevens Pass in particular, which experienced continuous heavy snow and rain for 86 hours, amounting to almost 70in of snow with about 7.5in of water equivalent. Not surprisingly, atmospheric rivers often go hand in hand with avalanche warnings, which were issued for 3 consecutive days at Stevens Pass from February 5th-7th, along with high danger in all other zones. Heavy rain fell at low elevations and even caused a significant mudslide on SR 410 between Enumclaw and Crystal Mountain, closing the road for 4 days and knocking out communications to 9 mountain weather stations for a week. As the AR exited the Northwest, and natural avalanche activity tapered off, conditions still remained touchy to human traffic on February 8th and 9th. Several triggered avalanches were reported that weekend, most notable of which was a close call near Mt. Baker Ski Area:
On February 8th, a skier was fully buried in an avalanche adjacent to Mt. Baker Ski Area. The avalanche was triggered by a traveler from a different party. Mt. Baker Ski Patrol was on the scene immediately, located the victim quickly, dug them out, and cleared the airway. The individual survived and reported no injuries. The avalanche was about 1ft deep and eventually broke up to 500ft wide. NNW aspect 5500ft. Photo: Mt. Baker Ski Patrol
Clear skies on Sunday, February 9th gave observers a chance to document the widespread avalanche cycle in the Stevens Pass zone that occurred February 5th-8th, including this view of crowns from large natural avalanches in the Berne Camp Chutes with Glacier Peak in the background. Photo: Matt Primomo
High Pressure before President’s Day Weekend
The week of February 10th brought the longest stretch of dry weather so far in 2020. A notable northwest wind event redistributed snow throughout the region and drove an isolated wind slab problem in most zones. Generally, it was the quietest few days avalanche-wise in weeks. However, a significant human-triggered avalanche occurred near White Pass on February 12th. Fortunately, no one was caught or injured. The incident provided a good reminder that even during periods of lower avalanche danger when avalanches are unlikely, outlier events can and do happen. The winter snowpack will always pose some level of uncertainty, and big triggers like cornice fall can produce surprising results.  Â
The crown of a human-triggered avalanche on a northeast aspect at 6700ft in the Hogsback area near White Pass. Two travelers unintentionally triggered a cornice, which dropped onto the slope below and triggered a very large avalanche. 2/12/20 Photo: White Pass Ski Patrol
Avalanche Problems
Loose Wet
Strong sun will soften the snow surface on steep southerly slopes by afternoon. So far, cool temperatures have kept Loose Wet avalanches to a minimum, but we could see an increase in these avalanches as the day warms. Monitor how much surface snow is warming and becoming wet. If you see fresh roller balls or warm, slushy snow, minimize your exposure to steep sun-aexposed slopes. Though often small, loose wet avalanches can have consequences in the wrong terrain. Avoid terrain traps like gullies and cliffs where you suspect wet avalanches.
Cornices remain large and overhanging on high alpine ridges. Minimize or avoid routes where these threaten from above, especially where they are exposed to direct sunshine. Warming and strong sun may weaken cornices during the day.
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: Possible
Expected Size: 1 - 1