Avalanche Forecast
Issued: Jan 27th, 2020 10:54AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Storm Slabs.
NWAC,
Northwest Avalanche Center
Very dangerous avalanche conditions are developing Tuesday. Snow will accumulate rapidly building large and dangerous slabs above a firm crust. Avoid terrain where avalanches can start, run, or stop including valley bottoms connected to open slopes at higher elevations.
Summary
Discussion
Above about 6000’ a firm rain crust exists. This layer is acting as a bed surface for recent large natural and human triggered avalanches. Multiple large avalanches were observed during brief clearing on Monday in White River and there is a very large crown in the West Crater.
Mt Hood is expected to receive 2.5 inches of SWE (snow water equivalent) in the next 24 hours. With rapid snow loading above a good sliding surface expect a large and dangerous avalanche cycle over the next two days.
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
Strong winds will rapidly transport new snow and develop fresh wind slabs. Slopes steeper than 35 degrees are the most likely place for an avalanche to initiate, but even if you are not on a slope that can avalanche, remember that very large and destructive avalanches may run very long distances into valleys. Avoid travel where an avalanche may start, run or stop.
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
Storm Slabs
New snow is rapidly stacking up tonight and more will follow Tuesday. Storm slabs are most likely during periods of heavy precipitation, which is what is forecast for Tuesday. Slabs may reach depths of 2 feet by Tuesday afternoon and will be weighted by continued snowfall. Avoid travel in avalanche terrain.
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.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Jan 28th, 2020 10:54AM
