Avalanche Forecast
Regions: Cascades - East.
Avalanche conditions will continue to be defined by elevation on Sunday. The most dangerous slopes may be at lower elevations, where weak, wet snow is having a tough time refreezing. New snow and wind will form slabs at higher elevations. Travel with caution, and monitor quickly changing conditions during the day.
Discussion
On Saturday, a couple of separate parties found wet slab avalanche concerns at and below 5,000ft near Blewett Pass. They experienced whumphing collapses, and identified a layer of very weak, wet grains down 1 to 2ft as the culprit. Up higher where the snow was dry, an observer found a medium sized recent (D1.5) storm slab from an east aspect at around 7,000ft in the Icicle drainage. Later in the day the new snow became sticky and they were able to trigger small loose wet avalanches on steep slopes. Ski patrol at Mission Ridge triggered multiple cornice blocks that initiated wind slabs 12" deep and up to 80ft wide. On Friday the 23rd, widespread wet avalanche cycles were observed in the East Central, Stevens Pass, and Snoqualmie Pass area. Expect another round of rain and snowfall overnight into Sunday, with a bump in westerly winds that may drift snow at upper elevations.Â
Demonstrating the propagation potential of a layer of weak, wet grains (ECTP, M). NW at 5,050ft near Blewett Pass. January 25, 2020.Â
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
Wet Slabs
Wet slab avalanches may become likely in areas where you find a snowpack less than 3ft deep at 4,500ft, such as the terrain near and east of Blewett Pass. All the snow from January is resting on a thin layer of very weak, wet grains from around New Years Eve. As more snow falls into Sunday and daytime temperatures warm up, it will continue to stress this layer. You are most likely to run into trouble from this problem on steep slopes below 5,000ft in elevation, where the surface of the snow has not yet refrozen and become supportable. Look for weak snow 12" to 20" below the surface. Wet slabs could be surprising and large. Plan to stay off of steep slopes at lower elevations, especially if you find punchy wet snow, or hear whumphing collapses.
Loose wet avalanches may occur as the daytime warms the new snow becomes sticky. Monitor for signs of instability such as rollerballs, wet snow, and recent fan shaped avalanches.
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Wind Slabs
A burst of new snow, along with moderate westerly winds may drift lower density snow into cohesive slabs. Look for these beneath exposed ridgelines and on open alpine terrain. Avalanches within new and wind loaded snow may become large on upper elevation slopes 35 degrees and steeper. Look for strong over weak layering and hollow sounding drifts of snow. Use small test slopes to check for signs of instability such as shooting cracks, and evaluate how the new snow is bonding. If you find signs of instability, steer around slopes steeper than 35 degrees.
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: Possible
Expected Size: 1 - 1