Bollettino valanghe

Mount Shasta

Mount Shasta Avalanche Center
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Pericolo valanghe

Sat
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto last year. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A combination of wind loaded snow, new snow, and a buried weak layer has spiked the hazard today. Natural avalanches are possible, and human-triggered avalanches are likely. Careful snowpack/weather assessment and conservative decision-making will be crucial for backcountry travelers. In terrain above treeline: travel on, near, or beneath slopes greater than 30 degrees is not recommended.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–3

    Storm slab instability will be on the rise today, with up to a foot of new snow expected. Over a foot could accumulate at higher mountain elevations. This problem will exist below and near treeline, and will likely be reactive to ski cut or snowmobile track. If triggered, these slabs could be large enough to bury or kill. Storm slab often becomes an issue when a significant amount of snow falls in a short period of time. With this system, moderate-high precipitation intensity (1-2 inches/hr) is expected through the day. As the day goes on, this problem will become more sensitive and dangerous.

    Yesterday, forecasters identified a widespread graupel layer across the Gray Butte area, below the two feet of new snow. We expect this graupel layer to present as a weak layer of some form in the snowpack. Today, as continued snowfall puts this weak layer to the test, avalanches could be extra sensitive, and fail larger than usual. Without seeing actual avalanches on the layer yet, it's hard to say how much impact it will have. That being said, today is a good day to be extra careful around steep slopes. If in doubt, give the snowpack time to adjust to the load, and stay out of avalanche terrain. 

    (3/13/2025)

    Photo take after a Compression Test. Visible is the graupel layer the column failed on. This weak layer could be an issue today as more weight is added to the mix

    Photo: Samuel Clairmont

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–3

    Wind slab will be a problem today on W-NW-N-NE-E-SE aspects, near and above treeline. Freshly formed wind slabs will likely be reactive to trigger, capable of failing large-very large, enough to bury and kill. Prior to this storm system, northerly aspects were already heavily wind loaded, as seen in yesterday's field observation. Today, strong-extreme southerly wind is expected, adding more weight to the same wind loaded slopes. With such high wind speeds, loading could happen quickly. Only a few hours of these wind speeds could be enough to produce a dangerous avalanche. If headed into the backcountry, diligently assess slopes for instability. Look for shooting cracks, lens shaped surface snow, and unusually deep snow conditions as indicators of wind loading. Avoiding this issue is simple, don't travel in wind loaded avalanche terrain. Above treeline, travel on, near, or beneath slopes greater than 30 degrees is not recommended.

    (3/13/2025)

    Wind lips on Gray Butte, south facing terrain. This is a great indicator of where wind loading is happening. In this photo, snow was transported south to north

    Photo: Samuel Clairmont

Avalanche Discussion

Dangerous avalanche conditions exist across the forecast area. If headed into the backcountry, keep your eyes peeled for signs of wind loaded slopes, new snow instability, and buried weak grains in the snowpack. If in doubt, stay off of steep slopes greater than 30 degrees. See something interesting? Send us an observation.

A Winter Storm Warning has been issued from 2 am this morning until 5 pm tonight. A foot or more is expected by this evening, with snow levels hovering below the level of Mount Shasta City. As of 6 am, four inches have already accumulated at Old Ski Bowl. Wind speeds will strengthen through the peak of this system, reaching strong-extreme speeds above treeline.

Yesterday, forecasters observed the Gray Butte area. Two feet of dry, loose, and relatively dense new snow was found throughout the area. Northerly aspects held wind loaded slopes near ridges and large terrain features. No natural avalanches were observed. A 1-2 cm layer of loose graupel was identified, on NW-W-SW-S-SE aspects, below the recent snow.  Upon ECT in multiple locations, this layer failed and propagated cleanly around tap 21. This layer could be an issue over the coming days, as new snow and more weight is added to the snowpack.

The Everitt Memorial Highway is CLOSED. For further road information: https://www.co.siskiyou.ca.us/publicworks/page/closures-and-delays

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