Avalanche Forecast
Issued: Feb 10th, 2019 10:10AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Dry.
NWAC,
Northwest Avalanche Center
We have unusual wind slab conditions in the West-North zone. These winds slabs may be difficult to see Monday due to more new snow. This is a good time to be cautious and avoid open slopes greater than 35 degrees especially at higher elevations and near wind exposed features such as ridgelines and passes.
Summary
Discussion
We received a report of a large, remotely triggered wind slab avalanche near Ptarmigan Ridge in the Mt Baker backcountry Sunday. This avalanche was approximately 2 feet deep and failed on a layer of sugary facets. We don’t see remote triggering of wind slabs very often. Events like this should cause us to stand up and take notice. Avalanche Details: 2/10/19: SW aspect, 5200 ft. 45-degree slope.
Photo: Remotely triggered wind slab from Sunday.
The recent and expected storm pattern hasn’t been favoring the West North area. That doesn’t seem to change going into Monday. Each of these storms (Friday-Saturday, and Sunday-Monday) are modest, especially by Mt Baker standards. That may just lead to very slow and incremental loading of the snowpack. When we get into situations like this, it’s tough to say when the snowpack will reach its tipping point. It may not be Monday, but only time will tell.
We want to call attention to the odd weather lately. It has been extremely cold for a long time. The snow is falling at very high snow-to-water ratios. This isn’t our normal Northwest pattern. In short: unusual weather often leads to unusual avalanches. Don’t get lulled to sleep an fall into normal travel habits. Keep your head on a swivel and watch the snow around you. If you see anything strange or surprising, that may be the snowpack telling you it’s ready to break.
Snowpack Discussion
New Regional Synopsis Coming Soon
Problems
Wind Slabs
This is not your normal wind slab set-up. 1: We have an unusual wind loading pattern, with wind slabs on numerous aspects. 2: The wind slabs may be hidden by new soft snow, making them difficult spot. 3: Wind slabs may sit on a layer of weak sugary facets, making them easier to trigger. And 4: There was a remotely triggered avalanche on Sunday. This is a time to be very cautious and avoid open slopes greater than 35 degrees if you suspect any wind transported snow occurred in the area. You are most likely to find a layer of facets below any recent snow on SE-SW aspects near and above treeline. In these areas, you may see unusual wind slabs behavior. You could hear whumphs, experience sudden collapses, or even remotely trigger 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 Dry
There will be even more loose, unconsolidated snow on the ground Monday. While loose dry avalanches can be easy to predict, don’t let them surprise you. If you are traveling near gullies or cliffs, keep this easy to manage problem on your mind.
Release of dry unconsolidated snow. These avalanches typically occur within layers of soft snow near the surface of the snowpack. Loose Dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs. Loose Dry avalanches can trigger slab avalanches that break into deeper snow layers.
Loose Dry avalanches are usually relatively harmless to people. They can be hazardous if you are caught and carried into or over a terrain trap (e.g. gully, rocks, dense timber, cliff, crevasse) or down a long slope. Avoid traveling in or above terrain traps when Loose Dry avalanches are likely.
Loose Dry avalanche with the characteristic point initiation and fan shape.
Loose dry avalanches exist throughout the terrain, release at or below the trigger point, and can run in densely-treed areas. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells.
Elevations: Below Treeline.
Likelihood
Expected Size
Valid until: Feb 11th, 2019 10:10AM
