Avalanche Forecast
Issued: Jan 23rd, 2020 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Storm Slabs.
NWAC,
Northwest Avalanche Center
Steer around all steep open slopes greater than 35 degrees where you could trigger an avalanche Friday. Obviously signs of unstable snow such as recent avalanches should cause you to pause and seek out low angled terrain away from avalanche slopes.
Summary
Discussion
Stormy conditions Thursday limited observations across the West-South region. However, we did receive reports from NPS staff of natural wet slab avalanches up to D2 in the near treeline band of Mt Rainier. Both the NPS and Crystal Mountain Ski Patrol verified smaller natural loose wet avalanches below treeline.
On Friday, cooling temperatures and a decrease in precipitation should allow for a slight downtrend in danger as wet avalanche problems become harder to trigger. This should be balanced by a developing and increasing dry snow avalanche hazard at upper elevations. You could experience very different dangers throughout the day with lower elevations being more dangerous in the morning and upper elevations more dangerous in the afternoon.
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).
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
Loose Wet
We’re forecasting loose wet, but you could run into any form of wet snow avalanche hazard. Linger wet slabs could exist above 5500’ where recent snow sits above a prominent MLK crust layer. At lower elevations, wet surface snow could remain as temperatures stay above freezing and may produce loose wet avalanches. Just because its snowing doesn’t mean you can’t trigger a lingering wet snow problem. With so much water in the snowpack, this unstable snow will take more than a few hours of cold to heal. Use caution when traveling in the mid and lower elevation bands by steering around all steep open slopes.
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: Treeline, Below Treeline.
Likelihood
Expected Size
Storm Slabs
New snow should continue to pile up throughout the day at mid and upper elevations developing new storm slabs. While we expect the new snow to bond well to the old surface, it’s hard to get past an additional 6-10” of snow. When you find more than 6” of new snow or see the wind drifted the snow deeper, steer around 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
Expected Size
Valid until: Jan 24th, 2020 10:00AM
