Avalanche Forecast
Regions: Cascades - North West.
Fresh and increasingly large slabs renew the dangerous conditions with heavy snow and strong winds transporting snow to the most reactive slopes in wind-loaded, steep terrain. Constantly check for and anticipate slopes with new snow 6” or more deep, sitting on an older, denser layer and steer around slopes 35 degrees and steeper. Avoid travel on or below steep rocky areas where glide cracks are opening up and steep rock faces are failing to produce large avalanches.
Discussion
Over the past 3 days, the Heather Meadows weather station (4200ft) recorded over 8in of new water and 20in of snowpack settlement. Precipitation came as rain up to 6000ft and saturated the snowpack. The full extent of the wet avalanche cycle is unclear as poor visibility has limited recent observations. However, glide cracks are widespread, and numerous glide and wet avalanches have run to at least size D2 (large). Loose wet avalanches were easy to trigger on steep slopes Friday, entraining significant snow and running far downslope.  Â
Precipitation will continue as snow levels lower to 3500-4000ft over the next 24 hours. As rain transitions to snow, fresh slabs will build at upper elevations and become reactive to human traffic. Despite the gradual cooling trend, the snowpack still needs time to recover from the recent rain event, and the lingering potential for glide and wet avalanches still has us concerned.
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 will drive the dangerous conditions near and above treeline due to heavy snowfall and wind creating fresh storm slabs. Winds will peak in the early morning hours (25-35 mph sustained at 5000 ft), while heavy snow developing after midnight Saturday night should continue through the day on Sunday. Slabs should continue to build throughout the day on Sunday and the distribution of large avalanches will increase as the snow piles up and makes this problem more widespread. Snow levels are difficult to predict during this storm, but we expect mostly snow above 3500 to 4000 ft with milder conditions limiting slab potential and snow accumulations below treeline. As you ascend in the terrain, look for signs of unstable snow, such as shooting cracks, settlement, or slab failure on small test slopes. Look for signs of wind transport to identify wind-loaded slopes where the largest and most likely slopes may be found. When in doubt, navigate around slopes steeper than 35 degrees.
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: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
Glide Cracks
Although we’re looking at a cooling trend, Glide Avalanches are caused by water running under the snowpack and as a result, it takes several days longer for the cooling to mitigate this problem than for other types of wet avalanches. With no sign of glide cracking, glide avalanches, and collapsing snow features on Saturday, we may be dealing with this problem for several days longer. Glide avalanche problems 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, where snow could shed from above creating destructive avalanches. 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