Avalanche Forecast
Regions: Olympics.
Expect snow and avalanche problems to change as you travel up in elevation in the Olympics. Be leery of steep slopes when you find a wet snow surface. Sticky snow, rollerballs, and small tear-dropped shape avalanches can clue you in that rain affect the snow.
Snowpack Discussion
December 26, 2019 (The regional synopsis is updated every Thursday @ 6 pm)
No matter where you are in the northwest, the snowpack looks a world different than it did a week ago. A major storm, widespread avalanches, developing weak layers, and an initially thin snowpack made for a hectic week. Let’s take a look at a few large scale trends for our holiday season.Â
A very large natural avalanche (D3) on the Shuksan Arm near Mt Baker that occurred during the storm cycle. Photo: Adam U.Â
Wet and Wild
“Some of the highest precipitation rates I’ve ever seen.†“Absolutely puking!†“Rivers running in the streets.†“Snowing snow hard I can’t see my hand in front of my face.†These were all statements we heard describing the wet and wild storm that impacted the Northwest from about Thursday (12/19) through Sunday night (12/22). Water totals were staggering in many locations (Table 1). For Hurricane Ridge, Mt Baker, Washington Pass, and high elevation terrain this deluge translated into significant snowfall. However, warm air in the central and southern parts of the region brought rain well into the near treeline bands. Whether your favorite spot saw rain or snow, four things are clear. 1. This was a huge loading event. 2. A widespread natural and triggered avalanche cycle (up to D3) occurred. 3. Avalanche danger spiked during and just after the storm before trending down through the week. 4. The snowpack changed dramatically.Â
Location
Precipitation 12/19-22
Hurricane Ridge
4.97â€
Mt Baker Ski Area
7.35â€
Washington Pass
3.53â€
Stevens Pass
6.28â€
Leavenworth
2.94â€
Snoqualmie Pass
7.89â€
Crystal Mt Ski Area
7.45â€
Paradise, Mt Rainier
6.57â€
Mt Hood Meadows
2.18â€
Table 1: Precipitation totals for select weather station locations December 19-22. Â Â
The Emergence of Persistent Slab Avalanche Problems
Coming out of this huge loading event, there was hope that many of the early season weak layers had been destroyed. Unfortunately, this was not the case in some locations. Old weak snow layers reared their heads in areas east of the Cascade Crest and near Crystal Mountain. While the exact extent and character of these layers can differ slightly, most locations are finding a layer of weak sugary facets associated with a crust about a foot above the ground. Persistent slabs are tricky to assess. Do not solely rely on snowpits and snowpack tests to help you choose terrain. How will these layers change going forward? Only time and observations will tell.Â
You may find weak sugary facets near a crust about 12 inches above the ground similar to what you see here. Photo: Jesse Charles
Low Tide Snowpacks During the Holidays
The storm this past week definitely helped the meager early-season snowpacks in all locations. Areas like Hurricane Ridge, Mt Baker, and Washington Pass experienced a jump of 20 or more inches in their snow depths over the past week. However, even with these increases, an early season snowpack still describes most locations. Expect numerous obstacles as you travel including open creeks, rocks, and trees. With this thin snowpack, limited access, and difficult travel we still have limited observations in some regions.Â
Open, deeply incised creeks in the Alpental Valley. Photo: Dallas Glass
Lack of information leads to a higher than normal degree of uncertainty. If you travel to higher elevations or more remote trailheads, recognize you could experience different conditions than the forecast suggested. You can help us fill in the gaps by submitting your observation here.Â
Happy Holidays!Â
-Dallas Glass
Avalanche Problems
Loose Wet
When you find new rollerballs or see snow shedding from rocks and trees you are encountering wet snow avalanche conditions. Steer around slopes greater than 35 degrees where you could trigger a loose wet slide. Even though we aren’t expecting much water with this weather system, any rain will be falling on a cold, dry, and layered snowpack. This is a big change for the snow. You may even see an isolated small slab avalanche as the snowpack struggles to transition to the warmth.
At lower elevations, there may not be enough snow to create a significant avalanche hazard. Instead, expect difficult travel with numerous obstacles to negotiate.
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: Possible
Expected Size: 1 - 1
Wind Slabs
If you travel above the rain/snow line, you could encounter wind drifted snow. Use your eyes to find clues such as fresh cornices, textured snow surfaces, and snowdrifts that indicate wind slabs may be nearby. Avoid steep convex slopes below cornices and when you find pillow-like snowdrifts. These wind slabs are now a day or two old and may be hard to trigger.
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.
Likelihood: Possible
Expected Size: 1 - 1