Avalanche Forecast
Regions: Cascades - North West.
The strong March sun will compete with increasing cloud cover Saturday to soften surface snow. If you see new loose wet avalanches, observe rollerballs, or experience soft surface snow deeper than your ankle, it’s time to change aspects. In the Mt. Baker area, the deep persistent slab problem has become highly unlikely to trigger. This does not mean impossible, but it would take a large trigger placed in an area of shallower snow where the weak layer/crust combination still exists. Continue to think about this when choosing terrain over the weekend.
Detailed Forecast
Slightly cooler and generally cloudier weather should be seen Saturday. Firm surface snow in the morning will be found in most locations. Be careful if you travel on these slopes before they soften. If you fall, it may be difficult to stop.
The loose wet potential will depend on the amount of sunshine received Saturday. On sunny slopes, if you see new loose wet avalanches, notice new roller balls, or experience soft surface snow deeper than your ankle, it’s time to change slopes. Be aware of high consequence slopes such as above cliffs or creeks where even a small loose wet avalanche may have high consequences.
In the Mt. Baker area, we have increased confidence that the deep persistent slab problem has become highly unlikely to trigger. This does not mean impossible, but it would take a large trigger placed in an area of shallower snow where the weak layer/crust combination still exists.
The following discussion on persistent slabs is still pertinent when choosing terrain this weekend:
 We have been talking about persistent and deep persistent slabs in the Cascades for a month now. This difficult to assess avalanche problem has resulted in fatalities each of the last three weekends. This is a classic low likelihood-high consequence scenario. Tracks on a slope do not indicate that it is safe. It may take a very large trigger or finding a shallower spot in the snowpack to cause a deep persistent slab avalanche. We continue to receive reports from professionals around the area demonstrating that the snowpack structure for this layer is still present. These same professionals are conveying that they are still avoiding large avalanche start zones as they travel. If you want to avoid triggering a deep persistent slab, stay out of large steep open areas.
Continue to use appropriate travel routes and techniques that minimizes your exposure to large overhead avalanche paths. Do not linger in locations where avalanches may run or stop.Â
Snowpack Discussion
At Mt. Baker, 6 inches of new snow accumulated Wednesday and bonded to an underlying melt-freeze crust. The thickness and supportability of this crust varies by location. On southern aspects the crust is typically 4-6 inches thick and growing, while on northerly aspects it is only 1-2 inches thick. Initially sunny skies Thursday and Friday created moist to wet surface snow on steep sunny slopes resulting in roller balls and small loose wet avalanches.
Below this most recent crust a variety of snowpack structures have been reported. Most observations indicate strong layers of dry snow intermixed with various melt freeze crusts. In isolated locations, thin buried persistent weak layers have been reported. You are most likely to find a buried persistent weak layer in shaded locations, at higher elevations, and/or in terrain slightly east of the Cascade Crest.
A more widespread deep persistent layer continues to be found 4-6 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 cannot prove its absences.
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.
Avalanche Problems
Loose Wet
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.
Aspects: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
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