Avalanche Forecast
Regions: Cascades - North West.
Low Danger does not mean no danger. Continue to use normal travel practices. Deep Persistent Slab avalanches are very difficult to trigger, but 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 over the past month.
Detailed Forecast
Low Danger means that triggering avalanches is unlikely but not impossible. While Deep Persistent Slabs are very difficult to trigger, the resulting avalanche could leave little chance of survival. Persistent weak layers have been the cause of avalanche fatalities or serious injuries every weekend for the past 4 weeks. Recent test results and avalanches show that these layers are still present, though getting harder to trigger. 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 large, complex avalanche paths.
You may see roller balls and small Loose Wet avalanches running on steep sunny slopes near rocks and trees. Until solar exposed slopes get softened by the sun they will remain hard and slick. It may be difficult to stop a fall on these slopes while they are still firm. Avoid traveling near or under areas with glide cracks and stay away from large cornices.
Snowpack Discussion
Expect warming temperatures and sun for Tuesday. While there may be some roller balls or small point releases, Loose Wet avalanches should not pose significant hazard. A dusting of light snow on Saturday and Sunday followed a warm, sunny stretch at the end of the work-week. Many sunny slopes have stout crusts in the top foot of the snowpack. At Mt. Baker, 6 inches of snow accumulated Wednesday, which quickly melted on sunny slopes. Mid to upper 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 are good for demonstrating the presence of a weak layer, they are not a decision-making tool to determining whether or not a slope is safe.
Observations
Baker
On Saturday, NWAC Observer Matt Primomo reported a large glide avalanche on a rock face on the south aspect of Mt Herman. The slope is known to commonly produce glide avalanches during warm conditions.
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.
Avalanche Problems
Deep Persistent Slabs
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 or near the ground. 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. They commonly develop when Persistent Slabs become more deeply buried over time.
Deep Persistent Slabs avalanches can be destructive and deadly events that can take months to stabilize. You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope.
A snowboarder triggered this Deep Persistent Slab near treeline, well down in the path.
Deep, persistent slabs are destructive and deadly events that can take months to stabilize. You can triggered them from well down in the avalanche path, and after dozens of tracks have crossed the slope. Give yourself a wide safety buffer to handle the uncertainty, potentially for the remainder of the season.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Unlikely
Expected Size: 1 - 2