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Avalanche Forecast

Archived

Mar 17th, 2018–Mar 18th, 2018

Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

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If the sun comes out, watch for Loose Wet avalanches on steep sunny slopes. While Deep Persistent Slab avalanches are now very difficult to trigger, the potential for high consequences lurks deep in the snowpack. Weak layers buried deep in old snow have been responsible for fatalities and serious injuries each of the past four weekends.

Detailed Forecast

Low Danger doesn't mean no danger. Continue to use normal caution while traveling in the backcountry. Any potential avalanches today will either be small or unlikely. The threat of Loose Wet avalanches lingers. If the skies clear and the sun makes an appearance, watch for uncohesive, wet snow on steep slopes. While Loose Wet avalanches are easier to predict and avoid, they can still be powerful enough to push you into trees, over cliffs, and through rocks. Use caution near these terrain traps on steep sun-exposed slopes. Until southerly slopes get softened by the sun they will remain hard and slick. If you travel on these slopes while they are still firm it may be difficult to stop a fall.

Recent warm temperatures and sun have brought up a host of other concerns. Avoid standing on or under cornices as they can easily break and fall.  Avoid glide cracks and stay out from under steep rocky terrain that is holding snow. 

In the Mt. Baker area, Deep Persistent Slab avalanches are now unlikely and difficult to trigger. This does not mean impossible, but it would take finding an area of shallower snow where the weak layer still exists to trigger an avalanche.If you manage to trigger one, the avalanche will be so large and destructive that you will have little chance of surviving. Persistent weak layers have been the cause avalanche fatalities or serious injuries every weekend for the past 4 weeks. Currently, you will see significant backcountry traffic in avalanche terrain, but little signs of avalanches. Test results and recent avalanches show that these layers can still be triggered. The best way to stay safe from the potential consequences is to limit your exposure to large avalanche paths. Stay out of start zones and complex terrain in large avalanche paths.

Snowpack Discussion

Light snow accumulations on Saturday and Sunday followed a warm sunny stretch at the end of the work-week. Many sunny slopes have very hard crusts in the top foot of the snowpack. At Mt. Baker, 6 inches of new snow accumulated Wednesday, which quickly melted on sunny slopes. High elevation, northerly slopes are staying soft and dry.

Below this most recent crust most observations indicate strong layers of dry snow intermixed with various melt freeze crusts. A more widespread deep persistent layer continues to be found 5-7 feet below the snow surface in the Mt. Baker zone. A thin layer of weak sugary facets have been observed just above a stout crust (2/8) on some aspects. Some snowpack tests (Compression Test and Extended Column Tests) will not be able to appropriately assess this deep weak layer. Deep Tap tests and Propagation Saw tests will yield the most reliable results. While snowpack tests may demonstrate the presence of a weak layer, they are difficult to interpret and are not a good tool for determining whether or not a slope is safe.

Observations

Baker

NWAC professional observer Lee Lazzara traveled to Ptarmigan Ridge Friday. New and recent wet loose avalanches, generally small, were visible on steep sunny slopes. Older wind slab found near and above treeline was unreactive. A thin sun crust from Thursday had extended it's reach to W-NW aspects. The 2/8 layer was down 6 feet in this area.

Lee was near Glacier Creek Thursday and found 3 to 8 inches of new snow well bonded to a forming melt-freeze crust. The 2/8 layer was down 6 feet in this area.

Problems

Loose Wet

Loose Wet avalanches are the 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. 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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.