Avalanche Forecast
Regions: Cascades - North East.
Friday will be a challenging day for backcountry travel. Significant and heavy new snow may stress recent storm interfaces. At lower elevations, saturated and punchy snow will create dangerous conditions. Plan to stay off of, and out from underneath steep slopes where avalanches may run and stop.
Discussion
Temperatures rose to 32*F at 6,600ft on Thursday, with heavy, wet snow falling. Many large, loose wet avalanches were observed in the neighboring East Central zone, with at least one very large slide (D3). Widespread natural avalanche cycles were noted, even with limited visibility in other areas of the state such as Snoqualmie Pass and Stevens Pass. The warm, wet weather will continue overnight Thursday into Friday. A gradual cooling trend and less precipitation should begin to limit natural activity on Friday. However, expect a saturated and messy snowpack at lower elevations. At upper elevations, all this heavy new snow will stress recent storm interfaces.Â
Recent, very large avalanche from a couple of east facing gullies in Tumwater Canyon, East Central Zone. January 23, 2020. Matt Primomo photo.
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
Storm Slabs
The storm snow will continue to accumulate into Friday. The new snow may bond well to itself, creating a slab. The added weight is creating a significant load on the colder, weaker, dry snow underneath. Previous observations showed a weak interface from around MLK weekend. In some parts of the zone, you may find a very thin crust buried 1-2 feet below the surface that formed around this time. This may also serve as a bed surface for avalanches to slide on. Give the snowpack time to settle and adjust to this new load, keeping off of, and out from underneath slopes steeper than 30 degrees for another day. Look for signs of instability such as recent avalanches, shooting cracks, and whumphing to confirm dangerous conditions.
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: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
Loose Wet
The snowpack is weak and wet at lower elevations. We expect the natural activity to begin slowing down into Friday, but loose wet avalanches will be easy to trigger if you go onto a steep slope that is saturated by water. As meltwater percolates through the previously dry snowpack, web slab avalanches may occur as well. A wet slab could be large, surprising, and difficult to manage. Stay off steep slopes that are saturated and punchy, and if you see recent wet avalanches.
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: Below Treeline.
Likelihood: Likely
Expected Size: 1 - 1