Avalanche Forecast

Slightly cooler and generally cloudier weather should be seen Saturday along the West Slopes of the Cascades. 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.

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. 

In most areas, 4-6 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 3-6 feet below the snow surface. A thin layer of weak sugary facets have been observed just above a stout crust (2/8). 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

Stevens

NWAC forecaster Dallas Glass was in the Stevens backcountry Wednesday. Dallas observed 6 inches of new snow bonding well to a semi-supportable and strengthening crust. He observed the 2/8 layer down 4 feet in most locations.

Snoqualmie

NWAC professional observer Ian Nicholson traveled in the Alpental Valley Wednesday. Ian found 6 inches of new snow bonding well to the newest crust. He observed several loose wet avalanches up to D2 in size occurring as the sun affected the new snow.  

South

NWAC professional observer Jeremy Allyn traveled in the Crystal backcountry Thursday. Jeremy found 6 inches of new dry snow moderately bonded to a newly forming crust. He observed limited new loose surface snow concerns on steep sunny slopes. The 2/8 layer was found down 4 feet.