Bollettino valanghe

Mt Hood

Apr 7 – 8, 2019Northwest Avalanche Center
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Archiviato · scaduto 7 years ago

Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
Apri la mappa completa

In sintesi

A powerful spring storm will cause very dangerous avalanche conditions to develop tonight through Sunday on Mt. Hood. Avoid traveling in avalanche terrain, especially in or near large avalanche paths that may release from higher terrain. Natural or human triggered wet snow avalanches are likely at any elevation where snow transitions to rain. 

Problemi valanghivi

  • Wind Slabs

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

    Strong winds and heavy snowfall on the upper mountain will build large and sensitive wind slabs Saturday night and Sunday. Sunday is not the day to try to nuance avalanche terrain above treeline.

    Before venturing into the storm and likely poor visibility, know your exposure to large avalanche paths (like the major canyons) with start zones located much higher on the mountain. Slab avalanches can entrain wet snow at lower elevations and become powerful and destructive.

  • Loose Wet

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

    Moderate to heavy rain will cause wet loose avalanches on steep slopes that see a transition from snow to rain. In the near to above treeline bands, wet snow avalanches may be large where they entrain more recent snow. Below 6000', wet loose avalanches will be smaller but can still be powerful. Avoid triggering a wet loose avalanche near a terrain trap such as cliff bands, open creeks, exposed or barely covered rocks and trees, etc, that would amplify the consequences of even a small wet loose avalanche. If you find wet snow deeper than your ankle, make the easy call to stick to lower angled terrain. 

Discussion

Snow and Avalanche Discussion

Mt. Hood is in the midst of a major storm cycle. Since it's spring, snowfall accumulations have been limited to a few heavy inches below 6000'. Above 6000', Mt. Hood Meadows patrol reported sensitive wind slabs ranging from 6" to a few isolated pockets of 2' on east to northeast aspects Saturday morning. Below 4000' the snowpack continues to melt away. 

Stormy conditions have limited reports on the upper mountain. As we get deeper into this storm cycle and if we see the amount of snow/water that's predicted, the potential for very large avalanches starting from the alpine and running far distances will increase. This is a good time to step back, avoid serious avalanche terrain and let the storm play out.

Snowpack Discussion

April 3rd, 2019

Spring snowmelt

The snowpack in much of the Cascades has changed dramatically in the past two weeks. The weather has shifted solidly to spring-like patterns. The spring warm-up started in mid-March with a prolonged period of relatively clear skies and warm temperatures. Moving into April, we’re seeing periods of unsettled spring weather bringing rain to many low and mid-elevation slopes and snow to upper elevations.

Very bare southeast aspects of Rock Mtn/Nason Ridge. April 2nd. Photo: Josh Hirshberg

Since the peak height of snow in mid to late February, mountain weather stations in the 4,000-5,000ft range show an average of 27% decrease in height of snow. Looking at weather stations in nearly every zone, the percentage decrease ranged from 22-29%. This year's spring snowmelt is much earlier than normal. Traveling in the mountains the loss of snow coverage is most noticeable on southerly, sun-exposed slopes and below 4,000ft. On northerly aspects and slopes above 5,500ft, the snowpack has seen less dramatic changes and has even maintained some dry layers.

NWAC climatological snow depth data from April 1st. You can view it on our website here.

Spring avalanche considerations

As you head into the mountains there are a few questions to ask yourself common to spring avalanche conditions:

  1. Is there any recent snow accumulation that could cause avalanches? If so, what kind of avalanches could you trigger? And where?

  2. What are the high and low temperatures of the past 24 hours as well as the forecasted temperatures during the time you’ll be in the mountains? Could these create weak, wet snow surfaces?

  3. How is the cloud cover contributing to the melting or freezing of surface snow? Did clear skies allow for a sufficient overnight freeze? Will the sun be strong enough to weaken surface layers?

Glide avalanches and holes opening up in rocky terrain near Mount Herman. Photo: Andrew Kiefer

Other considerations

In addition to daily avalanche hazard, the early snowmelt is creating some other travel considerations. Some roads and lower elevation slopes may not have enough continuous snow coverage for travel on snow machines. Holes melted around rocks, trees, and creeks could create a fall hazard. When nighttime temperatures and cloud cover allow for surface freezes, bring appropriate equipment to mitigate slip and fall hazard on steep slopes.

We are approaching the end of our daily avalanche forecasting season. The mountain weather forecast will continue into the spring, and the weather station data is available year round. Keep checking the forecast for conditions updates on the end of season information.

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