Avalanche Forecast
Regions: Snoqualmie Pass.
The snowpack around Snoqualmie Pass is generally strong. That doesn’t mean you can’t find a lingering wind slab. You are most likely to trigger an avalanche near convex rollovers, on unsupported slopes, or in complex terrain at higher elevations.
Discussion
Snow and Avalanche Discussion
We haven’t received much information since the weekend about conditions in the Snoqualmie area. However, the modest snow totals from Sunday/Monday should limit the avalanche danger.
There isn’t much new snow out there, but the snow on the surface is generally low density and unconsolidated. That means you may see loose avalanches. On shaded slopes, you may trigger loose dry avalanches. If the sun comes out, you may see wet surface snow on steep rocky slopes. Don’t let either of these small loose avalanches catch you by surprise, especially if you are traveling in high consequence terrain, such as near cliffs or gullies.
Snowpack Discussion
February 5, 2019
The active weather pattern this past weekend brought most areas a shot of new snow. Sadly, it seems like areas close to Seattle may have gotten more snow than the mountains. As a result, we are generally finding lower avalanche danger in most of our forecast zones. The general exception to this rule is the mountains closest to the Canadian border. The Baker area received 4†of water since January 31st. Here are a few general trends we see at this point.
The surface is where it’s at:
A combination of high elevation rains in January, a week of warm high pressure, and minimal new snow loads allowed most of our snowpacks to gain strength. In many locations, we are finding that proverbial Cascade “brick.†It’s not that you can’t find any weak snow in the mid- and lower snowpacks, but as a general rule, the snowpacks in our forecast regions are strong. Consequently, most unstable snow will be limited to the snow surface and the last interface buried in the most recent storm. For example, this week observers are primarily tracking the snow surface and the interface buried on February 1st or 3rd, depending on your location.
Very strong surface snow. This crust was buried in most locations Feb 1 or 3. Photo: Chip Daly
How can you use this? Keep your eyes open as you travel and look for areas that appear different. Why are they different? Could this be a rogue wind slab? Is the sun affecting the snow in this location more than other areas? Is the snowpack thinner and weaker in this area? When you find unique areas, it may be worth giving them a wide berth.
Still watching the far-east:
There is a lingering exception… areas east of highway 97 and east-slopes nearer to the Columbia River. As you travel further east in our forecast area, the snowpack gets thinner, weaker, and more variable. So, why are we seeing the avalanche danger go down in these locations? In general, there just isn’t a substantial slab over the buried weak layers. Two things could change that. 1. A wind event. One quick way to get a slab is to build one with some dry snow and moderate winds. That’s why we have wind affected areas on our mind when we travel to areas with thinner snowpacks. 2. A big storm. While areas like the Wenatchee mountains have seen their fair share of snow this season, these areas haven’t seen a big loading event. How would this weak snowpack handle a big storm? It’s hard to say at the moment. Just remember, if you go to mountainous areas around Twisp, the Wenatchee Mountains, or the East-South zone, you may encounter snowpacks with lingering persistent weak layers.
A shovel tilt test highlights weak snow interfaces in a very shallow east-side snowpack. Photo: Josh Hirshberg
The danger is real:
Even though the snowpack is strong and the avalanche hazard is generally low, there are other risks in the mountains that may pose a very real danger to backcountry travelers. The one we keep hearing the most about is very firm and slick surfaces. You are most likely to find icy surfaces in locations that did not receive much snow during this recent storm. When conditions are like this, it’s tough to gain traction, and any slip may result in a long uncontrolled fall.
Icy snow surfaces have been making travel conditions difficult, and sometimes dangerous. This firm, slick layer is buried below the most recent snow in many locations. Photo: Dallas Glass
What’s next?:
Given the strength of the snowpack, it will likely take a larger storm to ramp the avalanche danger back up. When will that storm arrive? We’ll keep watching the weather patterns and let you know. Make sure to check the latest weather and avalanche forecast before you head into the mountains.
-NWAC team
Avalanche Problems
Wind Slabs
Any small wind slabs are now a few days old. That should mean they are harder to trigger. If you are traveling into higher elevation or more extreme terrain, you may still find some of these lingering wind slabs. When we get into situations like this, we start thinking about slope features where it is easier to trigger an avalanche. You are most likely to trigger a lingering wind slab near convex rollovers, on unsupported slopes, or in more complex terrain. Keep your eyes open as you travel, and take a moment to identify slope scale features you want to avoid.
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