Avalanche Forecast
Issued: Jan 28th, 2020 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
Avalanche danger should peak during periods of heavier precipitation, blowing snow, and warming temperatures. Steer around specific features such as wind affected snow and steeper convex rollovers where you are more likely to trigger an avalanche.
Summary
Discussion
Weather forecast anticipates the warmest temperatures during the morning hours in the West South zone. This could combine with an increase in rain and snow. Expect the avalanche danger to peak during this time.
Areas of the West South accumulated 10-24” of snow during Monday night/Tuesday’s storm with the highest totals on the volcanoes. Information about avalanche activity in these areas was limited. In the Crystal backcountry, NWAC staff reported a small natural loose wet avalanche cycle on steep rocky southerly slopes late in the day. He also triggered a large storm slab with a cornice on an E aspect at about 6300’. This avalanche propagated widely and even reached into slightly lower angled terrain.
An intentionally triggered avalanche on Crown Pt. in the Crystal backcountry. Photo: Jeremy Allyn. SS-AC-D2-R1-S 10” deep, 200’ wide.
Snowpack Discussion
Update: January 24th 2020 (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.
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).
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.
Location
January 1-23 Precipitation (Water Equivalent)
Hurricane Ridge
14.79”
Mt Baker Ski Area
28.65”
Harts Pass
11.2”
Stevens Pass
20.26”
Leavenworth
4.01”
Snoqualmie Pass
25.43”
Paradise, Mt Rainier
24.13”
Mt Hood Meadows
22.34”
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.
Problems
Storm Slabs
Snow throughout the day Wednesday could form new storm slabs. We expect most of these to fail on subtle and short-lived weaknesses within the new snow. However, avalanches could step down into recent snow layers in larger terrain or at higher elevations. As of Tuesday afternoon, you could find 2 or more feet of snow above the most recent (1/25) crust. Avoid features where you will be most likely to trigger an avalanche. Steer away from very steep slopes, convex rollovers, and wind drifted snow. As you ascend in elevation, use caution and dial down your slope angles. Slabs in these areas could be larger, easier to trigger, and more difficult to manage.
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
Expected Size
Loose Wet
Warming temperatures and rain at lower elevations could drive another round of loose wet avalanches Wednesday. Small natural loose avalanches should be most likely in a narrow band where the snow experiences warm temperatures and rain for the first time (4000-5000’ in many areas). When you feel temperatures warm, see new rollerballs, or find fresh fan-shaped debris, steer away from steep slopes greater than 35 degrees. Keep the slopes above you in mind. You could encounter natural loose wet avalanches during the warmest and wettest times of the day.
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
Expected Size
Valid until: Jan 29th, 2020 10:00AM
