Avalanche Forecast
Regions: Stevens Pass.
Avalanche conditions remain dangerous as the potential for large wet avalanches lingers through Friday morning. As temperatures cool and rain transitions to snow, fresh slabs will build and become increasingly reactive throughout the day. Seek out lower angled terrain away from avalanche slopes.
Discussion
Stevens Pass received over 2in of water since Wednesday afternoon. Precipitation fell as snow overnight Wednesday before transitioning to rain early Thursday as snow levels climbed to 6000ft. More water (1-1.5in) is on the way over the next 24 hours as temperatures gradually cool with snow levels lowering to 4000ft by Friday afternoon.Â
A widespread natural avalanche cycle occurred Thursday on Stevens pass. The majority of avalanches were large (D2) with a few very large (D3) avalanches reported as well. Natural storm slab avalanches occurred first, and as snow transitioned to rain, wet loose avalanches began, and continued throughout the day.
Numerous natural avalanches on the SE side of Lichtenberg Mountain. In some start zones, storm slabs looked to have occurred first, before a wet loose cycle overran these crowns. 01/23/20 Photo: Matt Primomo
Snowpack Discussion
January 23rd, 2020 (The regional synopsis is updated every Thursday @ 6 pm)
January to Remember
A parade of storms since the New Year began brought relentless precipitation, and impressive snowpack growth throughout the region. Areas along the west slopes of the Cascades have rarely gone more than 24-48hrs without precipitation. In the past three weeks, the Volcanoes and Passes received 20-28in of water equivalent, translating into incredible snowfall totals - Mt. Baker Ski Area reported 240in of new snow since January 1. The majority of NWAC weather station sites are reporting snow depths well over 120% of normal for this time of year. Ongoing precipitation and fluctuating snow levels have maintained elevated avalanche danger throughout the month, with avalanche warnings issued for nearly all forecast zones on 4 separate days (January 6, 7, 12, 23). Â
Snow depth imagery for the Northwest Region on January 23, 2020. Many areas in the Cascades and Olympics show well over 100 inches of snow on the ground. Image courtesy of NOHRSC Regional Snow Analysis.Â
Location
January 1-23 Precipitation (Water Equivalent)
Hurricane Ridge
14.79â€
Mt Baker Ski Area
28.65â€
Harts Pass
11.2â€
Stevens Pass
20.26â€
Leavenworth
4.01â€
Snoqualmie Pass
25.43â€
Paradise, Mt Rainier
24.13â€
Mt Hood Meadows
22.34â€
Table 1: Precipitation totals for select weather stations January 1-23, 2020. Huge numbers at Baker, Rainier, Hood, and the Passes and there is still another week left this month.
MLK Weekend and a Pattern of Rain on Dry Snow
After a prolonged cold period with arctic air and lowland snow, MLK weekend brought unseasonably warm temperatures and a rapid thaw. High snow levels and rain caused wet avalanche activity throughout the region January 18-19. A few very large natural avalanches occurred at upper elevations where all precipitation fell as snow. A cooling trend followed, creating a pronounced crust that is now buried in almost all forecast zones. Cold, dry snow January 21-22 was followed by a rapid warm-up and the most significant rain on snow event yet, causing avalanche warnings on January 23 for 5 of our 10 forecast zones.
The crown of a very large avalanche around 10,000ft on the Newton Headwall of Mt Hood which likely occurred during the storm late last week. 01/19/20 Photo: Kevin Kayl
The buried MLK crust is widespread throughout the region and a prominent marker in the snowpack. Crystal Backcountry 01/20/20 Photo Jeremy Allyn
One More Week To Go
January isn’t over yet, and the long term forecast continues to show an active and wet weather pattern for the Northwest. The low-snow, drought-like conditions of the early season seem like a distant memory at this point. We’ve certainly made up for lost time in 2020, and this already impressive month looks to end with a bang.
Avalanche Problems
Loose Wet
We are at the tail end of a significant natural avalanche cycle. The snowpack may still be capable of producing surprising wet avalanches. Loose wet avalanches could build significant mass as they run downslope and pack quite a punch. Concern for wet slab and glide avalanches will linger overnight and into Friday morning until cooling temperatures arrive by afternoon. These avalanches are difficult to predict and even harder to assess. Build in a wide margin for error if you venture out on Friday, and steer around slopes 35 degrees and steeper.
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
Storm Slabs
With a cooling trend throughout the day, fresh slabs may begin to form as low as 4000ft. Slabs will be stiffer and more reactive in wind loaded terrain. Avalanches within new and wind loaded snow will be easy to trigger on upper elevation slopes 35 degrees and steeper by Friday afternoon. These avalanches could easily entrain wet heavy snow as they run onto lower slopes becoming more dangerous and destructive. Give the snowpack time to adjust. Ease into terrain slowly and avoid large open slopes 35 degrees and steeper.
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: Likely
Expected Size: 1 - 1