Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

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3 · Marcato
Limite del bosco
2 · Moderato
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In sintesi

You can trigger a large avalanche where snow and wind increase the danger on upper-elevation lee slopes. Use small test slopes to evaluate the bonds between cold snow and recent crusts before engaging with terrain steeper than 35 degrees. Warming at lower elevations will destabilize cold snow, forming sticky wet snow that can slide on any open slope steeper than 35 degrees.

Problemi valanghivi

  • Wind Slabs

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

    Large slabs will build as periods of moderate snowfall get redistributed by moderate winds favoring loading on the northern half of the compass.  We're expecting 0.8" of water equivalent, which could translate to 6-10" of snowfall at upper elevations.  Mild temperatures may not permit much wind transport until you ascend above the freezing line (which may line around 6000 ft on Sunday). Above that elevation, expect a rapid increase in avalanche danger. Use visual clues such as active wind transport, fresh sharp cornices, sastrugi, and scour around rock features to identify the sides of ridges that are receiving wind loading. Avoid all steep or steep wind-loaded slopes at upper elevations and anywhere you expect winds could have drifted 6" or more of snow onto a slope. Remember that it may only take a few inches of snow to form a 6" slab given sufficient winds and time. Banded precipitation will elevate danger during the periods when you have less visibility (periods of heavier snowfall and stronger winds). Keep safe exit routes available so you don't have to navigate higher consequence terrain if you experience a whiteout.

    Up to around 6500 ft, these slabs will build on a crust; above those elevations, expect a new/old snow interface. Evaluate the interface in your terrain and test whether the new snow shears off the interface as a slab.

    Example: You may find surfaces like this on upper elevation, exposed aspects. A very obvious sign of recent wind transport and loading on the opposite side of a nearby ridgeline.

    Photo: Joseph Dellaporta

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5

    Lower elevation terrain east of Mt Hood hasn't experienced above-freezing temperatures in over a week. There's plenty of gradually settling cold, dry snow at these elevations. As southerly winds scour out the cold air pooled at these elevations on Sunday morning, expect small natural or human-triggered avalanches that could easily ruin your day. Terrain traps remain plentiful at these elevations and an avalanche could easily bury you. Seek slopes lower than 35 degrees and avoid exposure to terrain traps where you could be buried. At lower elevations, these wet loose avalanches could surprise you. At middle elevations where crusts existed on most aspects, any wet loose activity would remain above the 1/20 crust, involving only 1-3" of heavy, wet snowfall from Saturday night and we don't expect it to be a problem.

    Even a small wet loose avalanche could do damage, particularly when paired with a terrain trap. 

    Photo: Mt Hood Meadows Patrol (4/11/23)

Avalanche Discussion

Saturday was a rare day of quieter weather with only a skiff of snow on Mt Hood. Over 5" of snow water equivalent has fallen on Mt Hood since 1/16. Temperatures cooled following a warm frontal passage that ended with a freezing rain event. This freezing rain event mostly affected elevations between 4200-4500 and 6500 ft. A skiff of snowfall buried this 1/20 crust on Saturday and we'll wait for more precipitation to arrive Saturday night through Sunday to see how well it bonds. 6-12" of cold, dry snow sits between the 1/20 crust and a more broadly distributed 1/16 crust extends from 4500 to around 8500 ft. Most avalanche activity will involve or remain above the 1/16 crust (storm snow). Once the 1/20 crust fades away, a larger avalanche could involve the 1/16 interface. You can read more about these crusts in this observation from Tilly Jane (photos in Gallery).  Similar reports came from the N side of Mt Hood and the south side ski areas at these elevations. Winds were starting to drift shallow snow above 6000 ft onto the surface crust. 

Inversions on Mt Hood have meant that mid-elevations have warmed more in recent days than lower elevations. Therefore, lower elevations are more susceptible to a warm-up than middle elevations where crusts already exist. Wet loose avalanches were easy to trigger at mid-elevations on Friday.

Although we're removed from the recent very large avalanche cycle, we'll leave some of the evidence in the gallery. These avalanches likely occurred during the peak of the recent storm cycle. One slide likely ran several thousand feet from Wy'East face during a period of intense precipitation and extreme winds Wednesday afternoon or evening. 

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