Avalanche Forecast
Regions: Cascades - North West.
We keep adding a lot of water to the snowpack and as you ascend to the top of the near treeline and above the snowpack should become much drier with large storm slabs you can trigger on slopes steeper than 35 degrees. Near and below treeline, mild temperatures and running water continue to drive a lingering, but high consequence threat of glide avalanches, cornice falls, and glide cracks. Maintain distance between yourself and areas where glide cracks are opening, water is running, or cornices sagging and may fail on the slopes above.
Discussion
Near treeline and below, the most dangerous conditions were likely due to an ongoing glide avalanche cycle on Friday, Saturday and Sunday. Mt. Baker received heavy rain and snow in the last 12 hours, picking up 1.38†of snow water equivalent with snow levels generally hovering around 4000 ft, but with rain getting up to 4500 ft or so. The copious amounts of water running through the snowpack largely result from the 8†of water which hit the snowpack from Wednesday evening 01/22 through Friday evening 01/24. Most of that came as rain up to 6000 ft, creating 20†of snowpack settlement. On Friday through Sunday, Mt. Baker Pro Patrol observed saturation down several feet deep, with pillows collapsing and slabs up to 4 ft deep moving on smooth, steep rock faces, particularly where water drains under the snowpack. Lots of glide cracks were opening up at the ski area. The threat of glide avalanches, opening cracks, and collapsing pillows forced the ski area to close some steeper terrain on Saturday and Sunday.Â
On Sunday, limited visibility from the ski area afforded views of recent D2-2.5 debris from cornice fall or potentially glide avalanches. This debris is another indication that the snowpack needs to refreeze significantly before we’re done with these problems.
Snowpack settlement has dropped close to zero and below the variable amounts of fresh snow (up to 5†on Pan dome, with lesser amounts lower down), a slightly firmer bed surface lies above a fully saturated mid-pack that you can still sink your leg into.
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
Mild temperatures have made storm slab prediction difficult. In general, snow tends to be gluing to wet or old snow and this will likely continue to occur even as temperatures slightly Sunday night. Above treeline, in particular, storm slabs should build on snowfall from Sunday to produce slabs that may be large. Or, you may find that the slabs are smaller in size, primarily confined to the snow falling Sunday night with a potential thin-crust interface (bed surface) formed by the mild temperatures producing a bed surface. Use frequent hand shear tests to check the bond between the new snow and recent interfaces. If you find evidence of slab formation, avoid slopes steeper than 35 degrees and expect avalanches to be larger and more reactive if you ascend higher.
Cornices have been sagging and may still be primed for failure with additional loading. Give these features a wide berth, particularly where they may trigger a storm slab on a steep slope.
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
Glide Cracks
The mountains continue to struggle to cope with the mild temperatures and persistent precipitation they have received. Water continues to drain the snowpack with continued production of glide avalanches, glide cracks and collapsing pillows, although some of this activity has decreased as many of the potential rock slabs where glides occur have shed their snow. Settlement rates have also decreased significantly. Late in the day on Sunday we’re finally getting a bit of a cooling trend, but it’s too little too late for reducing the free-flowing water enough to do more than slightly reduce the risk of glide avalanches. Remember that glide avalanches fail without warning and the way to deal with the problem is to avoid terrain where they may occur. Avoid travel on or underneath steep rocky slopes and cliff bands, anywhere snow could shed from above you and imperil you. Give any steep slopes with visible glide cracks a wide berth. Travel cautiously and build in a wide margin for error.
A release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often preceded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
Predicting the release of Glide avalanches is very challenging. Because Glide avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide avalanches.
This Glide avalanche broke to the ground on a smooth, grassy slope. From all the mud on the bed surface, water pooling at the base of the snowpack likely caused the failure.
Glide avalanches occur when water lubricates the interface between the snowpack and the ground. These avalanches are difficult to predict and best managed by avoiding terrain below glide cracks.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 2