Avalanche Forecast
Regions: Snoqualmie Pass.
With both rain and snow in the forecast Sunday, fresh slabs may build at upper elevations and become reactive to human triggers while the lower elevations may receive rain. The saturated snowpack still needs time to recover from the last rain event, maintaining the potential for lingering glide and wet avalanches. Signs of instability like shooting cracks or other avalanches can key you into instability and should steer you away from avalanche terrain.
Discussion
On Saturday morning, Alpental Pro Patrol triggered a size D3 avalanche with explosives, which gauged into the old wet snow from the past few days. Add this to the list of notable avalanches observed since Thursday morning as the Snoqualmie Pass zone has gone through an impressive avalanche cycle. Peak instability during the cycle lasted from Wednesday night through Friday morning, with professionals around the zone reporting widespread natural avalanche activity up to size D2.5. These avalanches were all wet in nature, with Wet Loose, Wet Slab, and Glide avalanches all being observed, and often intermingled. As the Alpental slide Saturday morning shows us, rain from the past few days still sits within the snowpack even after peak instability, and wet avalanches may still occur. With better visibility on Saturday, many glide cracks and further evidence of glide avalanches were observed. These lingering avalanches may become large and are most likely on big alpine terrain features, slopes containing glide cracks, or unsupported slopes such as cliff bands that did not naturally avalanche during the previous cycle.
Large debris from a size D3 wet avalanche triggered by Alpental Patrol Saturday morning. Photo: Aaron Opp
Snowpack Discussion
Update: January 24th 2020Â (The regional synopsis is updated every Thursday @ 6 pm)
During the afternoon of January 23, 2020 one person was buried and killed by an avalanche that released from the roof of a home north of Blewett Pass near Highway 97. The elevation was approximately 1,700ft above sea level. She was found underneath 4 to 5ft of debris. She was discovered and excavated some time after the accident, where CPR was performed. Additional emergency response arrived within 15 minutes, but they were unable to revive her.
Our deepest condolences go out to the family and friends of the victim.
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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
Storm slabs may be present near and above treeline Sunday, especially above ~4000 feet where precipitation is expected to be all snow. Slabs may be drier and deeper as you ascend in elevation or in areas where winds have deposited new snow on lee slopes. A mix of snow, rain, freezing rain, and sleet on Saturday has created a new thin crust on the snow surface for any new snow to fall on in many locations. Use small test slopes and hand pits to investigate the bond between the new snow and the existing surface. If you find a poor bond and more than 6 inches of cohesive snow, avoid slopes greater than 35 degrees.
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: Possible
Expected Size: 1 - 1
Loose Wet
Wet Loose avalanches often start at a point and can entrain lots of snow as they travel downhill, even triggering slabs as they descend. Rollerballs, pinwheels, and fan-shaped avalanche debris are signs that wet loose avalanches are possible. Steer around slopes greater than 35 degrees and avoid terrain traps such as creeks, gullies, or cliffs if you notice these signs or witness a switch from snow to rain.
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: Possible
Expected Size: 1 - 1