Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The spring transition continues in the upper snowpack, leading to periods of instability as the sun breaks down surface crusts and previously dry snow becomes moist, sticky, and prone to loose avalanches. At the highest elevations on shaded slopes, drifts may retain reactivity in isolated locations and you can still trigger them in more extreme terrain.

Problemi valanghivi

  • Loose Wet

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

    We're expecting another solid overnight refreeze Saturday night, with even warmer temperatures on Sunday balanced by increased SE wind speeds that may keep thickening surface crusts frozen long. On aspects that are crusty in the morning, note the transition as they start to break down into drier snow underneath. That is the time to step away from steep slopes and out from under bigger exposed terrain. Where crusts are not supportable or non-existent to start the day, rollerballs, pinwheels, and moist, sticky snow gives you the clue that wet loose avalanches are not far behind.  Natural avalanches have an increased likelihood in the highest elevation areas where crusts are thin. Rocks and cliffs will warm quickly in the sunshine, shedding chunks of snow or ice that could initiate an avalanche on the slopes below. While the danger is moderate at middle and upper elevations, expect the day to start out with low danger, with an increase in danger in the mid-day and afternoon hours. Winds and thin high clouds will battle freezing levels approaching the top of Mt Hood to determine when your aspect and elevation experiences this transition. 

    Example: Solar triggered loose wet avalanches running far distances in high elevation terrain.

    Photo: Andrew Kiefer

  • Wind Slabs

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

    Thanks to very mild temperatures the likelihood of triggering wind slabs continues to trail off after the storm, and surface crusts will limit wind slab activity to upper elevation shaded slopes. Large, thicker wind deposits will be slowest to heal and also the most hazardous. Now that we're 4 days out from the wind loading event, you're unlikely to get much feedback. The risk now focuses on extreme terrain with steep, unsupported  lee slopes. Treat very steep textured snow surfaces in at the highest elevations with caution. And keep in mind that large blocks of snow or ice falling off rocky terrain, or cornice fall, might also serve as triggers on wind-loaded slopes below.

    Example: Shooting crack on a wind textured or crusted slope with punchy layering.

    Photo: Joe Dellaporta

Avalanche Discussion

This will be the last avalanche forecast for the 25-26 season. Mountain weather forecasts will be published each afternoon through May 3rd. NWAC will continue to monitor conditions and issue special avalanche bulletins and warnings as needed. A huge thanks to everyone in our community for your support this winter!

1.5-2 ft of storm snow that fell Tuesday afternoon through April 14-16 continues to transition toward a spring snowpack. It sits above a firm, slick and widespread 4/14 crust, which is still exposed in a few wind-swept areas. Observers on the south side of Mt Hood found dry snow above 9000 ft, and thin, but ski supportable crusts below with excellent corn snow around 11 AM. Below 6000 ft, the snow was becoming moist/wet and wet avalanche activity was likely soon to follow. Slope testers were enjoying steep slopes without triggering wet activity before there were signs of surface crusts breaking down. But, they might not have been as fortunate on the same slopes in the afternoon. This pattern is likely to play out once again on Sunday. 

That warming trend continues into Sunday as freezing levels remain above NWAC forecast elevations. Free air temperatures may remain above freezing, but snow surfaces are expected to refreeze thanks to clear skies and increased winds. If that refreeze doesn't occur, conditions could become more dangerous than forecast as the warming trend will impact more deeply into the upper snowpack. We're expecting crusts on sun-exposed aspects up to the top of Mt Hood and dry snow on shaded slopes above 8000 ft, so if you don't find crusts when you expect them, reduce your exposure to steep slopes in light of the uncertainty.

Observers also noted a lack of cracking on the highest elevation wind-loaded test slopes . This doesn't mean unstable wind slabs can't be found, but many of the smaller deposits of wind drifted snow are quicker to stabilize and become unreactive. They also found some areas of less wind affected snow on the upper mountain, an unusual occurrance. Wind slabs were more reactive during and just after the recent storm with human triggered small wind slabs in the Mt Hood Meadows backcountry both Wedesday and Thursday. Also on Thursday, observers in Devils kitchen on the upper mountain found a reactive mid-storm interface and widespread cracking within the 2 ft of recent storm snow sitting above a thin crust. 

Remember that the recent snow has fallen on a far below-normal snowpack. Windward  and south-facing slopes are either mostly snow-free or melting out fast up to middle elevations. Exposed or barely covered rocks can exacerbate any fall or avalanche so it's wise to reduce your speed accordingly on the descent. Where snow exists at lower elevations, it the new snow is likely transitioning much more rapidly and danger is expected to be isolated. Slick crusts may be forming on the snow surface once again and could be dangerous before the sun warms them up. Make sure you have sharps and know how to use them as we transition back toward spring travel conditions.

If you plan to head to Mt Hood Meadows or Ski Bowl for uphill use, please remember these ski areas are now closed for the season and avalanche mitigation is longer being conducted. Treat this terrain like a backcountry snowpack and carry avalanche rescue gear.  

Are you heading out? You can help the forecast staff and backcountry community out by submitting your observation here or on the AvyApp.

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