Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Continued warming and rain will prolong very dangerous avalanche conditions. Wet avalanches of all types are likely and will be unpredictable. You could trigger wet avalanches on steep terrain, or they could run naturally from above. Avoid steep slopes, and don't linger in gullies or runouts from large, steep slopes at higher elevations.

Problemi valanghivi

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    Avoid traveling on steep slopes and, at upper elevations, steer clear of any areas where avalanches may start, run, or stop. If rain is falling on dry snow, wet loose avalanches will be more likely and more widespread. Natural wet slabs are unpredictable, so if you're traveling in the mountains, make sure you are aware of any overhead hazard from the terrain above you. Travel quickly through runouts and gullies where large avalanches can channelize and run long distances into lower elevations. Cornice failure and glide avalanches involving the entire season's snowpack should also be on your radar. Don't linger below deep, open glide cracks and overhung cornices. 

    Wet loose and wet slab avalanches will still be fairly widespread on Monday. While an initial round of avalanches occurred with rain and warming on Sunday, upper elevations likely did not see much rain. The snowpack is dry and layered with multiple weak interfaces, especially the January Drought Layer. So, with rain and additional warming, water will percolate farther through the snowpack, and much larger and unpredictable wet slab avalanches are likely. 

    (3/2/2025)

    A wet slab avalanche ran thousands of vertical feet and crossed the Hart's Pass road in the East North zone earlier this month.

    Photo: Katie Warren

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Additional snowfall and strong winds at the highest elevations will create large, sensitive wind slabs on steep lee slopes below ridgelines and exposed alpine terrain features. Avoid steep terrain where you see blowing snow, stiff pillow-like drifts, or textured surfaces. Cornice formations also point towards wind-loaded slopes below. Storm slabs will also be likely at elevations with dry snow. You can watch out for signs of instability, such as long, shooting cracks. But simply sticking to low-angle, sheltered terrain will be the best option for these dangerous avalanche conditions.

    (3/22/2025)

    A very large natural wind slab avalanche was observed near Mt. Tiffany on 03/22. (NNE, 7500 ft). It may have been initiated by cornice fall.

    Photo: Public

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    You may still be able to trigger large avalanches on an old, weak layer about 3 feet below the surface. The snowpack is shallower, and the layer is more well-developed near and east of Harts Pass and Mazama. Further west, near Washington Pass and Rainy Pass, these avalanches are less likely. 

    That said, rain on snow could bring this problem back in other areas of the zone if liquid water works its way all the way down to weak snow. While these avalanches will likely be harder to trigger this time around, this current storm and persistent weak layer setup are very similar to the previous atmospheric river in Late February, where a rider was killed in an avalanche near Hart's Pass. You can deal with this low likelihood, high consequence situation by avoiding steep northerly slopes with shallow and variable snow cover in the eastern part of the zone. To identify the weak layer, you can dig profiles and use snowpack tests (deep tap and propagation saw tests). When in doubt, defer to lower-angle slopes and simpler terrain.

    (3/17/2025)

    A widely propagating avalanche near Tiffany Mtn.

    Photo: Willie Webster

Avalanche Discussion

We are headed into day two of an atmospheric river, and temperatures will continue to warm. By Monday evening, freezing levels will reach the upper extent of our forecast area. Strong winds and precipitation will be most intense overnight and into the early hours of Monday but will be slow to let up throughout the day. The highest elevations may not transition to rain until later in the day. Expect avalanche activity to increase and very large persistent slabs to become more likely as temperatures continue to increase throughout the day. Travel will be arduous in deep, wet snow at most elevations on Monday. 

Recent storms have totaled over 2 feet near Washington Pass, with less further east in the zone. Throughout the past week, observers have reported a number of small natural and triggered wind slab avalanches. Many were small (D1), but a number of avalanches were big enough to bury or kill a person (D2).  These occurred in both leeward, wind-loaded slopes as well as sheltered terrain. Yet another report of someone getting caught and carried in a wind slab avalanche came through down in Steven's Pass. That makes 6 involvements in the last 10 days.

An old weak layer (the January Drought Layer) is buried 2–3.5 ft (70-120cm) below the surface but shallower east of Mazama. Near Rainy and Easy Passes, the JDL is over 4 feet deep and capped with a thick melt-freeze crust. In many parts of the zone, the JDL has rounded and gained strength. However, in the past week, observers have continued to report snowpack tests that have produced sudden and propagating results on Silver Star Mountain and near Harts Pass. On March 17, an observer near Tiffany Mountain reported widely propagating recent natural avalanches and rolling collapses on a weak layer in the middle to lower half of the snowpack. Then, on March 22nd, another observer documented a recent natural slab avalanche near Mt. Tiffany that looks deep enough to have potentially released on the JDL.

NWAC Forecasters visited the site of the avalanche fatality near Harts Pass that occurred on 2/28. The full accident report is published and can be found HERE. 

Submit an observation to the website or the Avy App to help NWAC Forecasters reduce uncertainty. It can be short, simple, and even anonymous. 

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