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 Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
A warmer storm arriving on Wednesday will bring wet snow concerns at lower and mid-elevations and build deeper winds slabs above treeline. With overlapping avalanche problems, choose simple terrain to travel safely. Limit your exposure to terrain connected to large avalanche paths that originate from the upper mountain.
Summary
Discussion
Storm totals through Tuesday afternoon showed 16-20 inches of new snow that came with continuous strong SW winds near and above treeline. Mt. Hood Meadows pro-patrol triggered widespread large wind slab avalanches on N through SE aspects near and above treeline Tuesday. Below treeline the snow was less reactive but avalanches took on wet snow characteristics in areas they were triggered. A firm crust can be found underneath the recent storm snow above 6000’. This crust provides a marker for how deep avalanches could break, especially at upper elevations.
A very large crown is visible in the West Crater. This avalanche (which occurred above the elevations that NWAC forecasts for) released Sunday running on the recent rain crust. The crown height was estimated at 8-10 feet. Photo: Timberline lift maintenance dept. 1/27/20
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
Wind Slabs
Winds will certainly be strong enough to transport new and recent snow above treeline Tuesday night through Wednesday. Avoid steep open slopes with wind drifted snow where you are likely to trigger a large wind slab avalanche.
Even for a place that gets as much snow as Mt. Hood, January has felt like one long continuous storm cycle. You still need to think about what’s happening high on the mountain and limit your exposure if crossing canyons and gullies at lower elevations connected to terrain capable of producing very large avalanches.
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
As snow turns to rain at lower and mid elevations Wednesday, loose wet avalanches will become increasingly likely. While loose wet avalanches at lower elevations may be small and hard to initiate, above 5000’ wet avalanches can entrain significant amounts of new snow and become large and dangerous.
At any elevation where you find wet unconsolidated surface snow, avoid slopes steeper than 35 degrees, especially near cliffs, creeks and other terrain traps. If you see natural loose wet avalanches, rollerballs or pinwheels, it’s time to move to lower angled terrain.
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
Valid until: Jan 29th, 2020 10:00AM
