Bollettino valanghe

Mt Hood

Feb 5 – 6, 2019Northwest Avalanche Center
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Archiviato · scaduto 8 years ago

Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
Apri la mappa completa

In sintesi

Shallow cold, dry snow may be drifted into slabs or may be hiding older wind slabs, especially at higher elevations. Small loose snow avalanches may catch you on shady or sunny slopes in steep terrain and if the sun hits a slope directly.       

Problemi valanghivi

  • Wind Slabs

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

    While winds have eased, expect slowly healing wind slabs formed since February 1st and increasing hazard with elevation. The Mt Hood area picked up about 5-10 inches of increasingly light, dry snow Saturday night through Tuesday morning while moderate to strong and shifting winds (including N and E) have moved this snow around onto atypical aspects. Approach steep unsupported slopes with wind-drifted snow cautiously, testing for firm or hollow sounding snow as a sign that wind slabs may be present. You can stay safe by traveling on ridges, wind-scoured areas and any slope less than 35 degrees.

  • Loose Wet

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

    While you may be able to trigger loose avalanches on any aspect they will be easier to trigger and more consequential if the sun comes out and shines directly on the cold snow on Wednesday. Temperatures can limit the sun’s effect on the surface snow, but don’t think they will eliminate it. You may find moist to wet snow on steep, rocky slopes. When this occurs, expect small, natural, loose avalanches. On northerly aspects, small Loose Dry avalanches may be triggered on slopes approaching 40 degrees or greater. Don’t let these small avalanches catch you off guard or push you into a terrain obstacle, especially if you are traveling around higher consequence terrain.

Discussion

Snow and Avalanche Discussion

The Mt Hood area picked up about 6 inches of very light, dry snow Sunday night through Monday. Strong ridgetop winds from the North - East may have formed wind slabs on more a-typical slopes. The cold low-density snow may be poorly bonded to a hard firm underlying crust. Cold temperatures, should keep the surface snow cold and dry on any slope not receiving direct sunshine and easily transported by winds.

Snowpack Discussion

February 5, 2019

The active weather pattern this past weekend brought most areas a shot of new snow. Sadly, it seems like areas close to Seattle may have gotten more snow than the mountains. As a result, we are generally finding lower avalanche danger in most of our forecast zones. The general exception to this rule is the mountains closest to the Canadian border. The Baker area received 4” of water since January 31st. Here are a few general trends we see at this point.

The surface is where it’s at:

A combination of high elevation rains in January, a week of warm high pressure, and minimal new snow loads allowed most of our snowpacks to gain strength. In many locations, we are finding that proverbial Cascade “brick.” It’s not that you can’t find any weak snow in the mid- and lower snowpacks, but as a general rule, the snowpacks in our forecast regions are strong. Consequently, most unstable snow will be limited to the snow surface and the last interface buried in the most recent storm. For example, this week observers are primarily tracking the snow surface and the interface buried on February 1st or 3rd, depending on your location.

Very strong surface snow. This crust was buried in most locations Feb 1 or 3. Photo: Chip Daly

How can you use this? Keep your eyes open as you travel and look for areas that appear different. Why are they different? Could this be a rogue wind slab? Is the sun affecting the snow in this location more than other areas? Is the snowpack thinner and weaker in this area? When you find unique areas, it may be worth giving them a wide berth.

Still watching the far-east:

There is a lingering exception… areas east of highway 97 and east-slopes nearer to the Columbia River. As you travel further east in our forecast area, the snowpack gets thinner, weaker, and more variable. So, why are we seeing the avalanche danger go down in these locations? In general, there just isn’t a substantial slab over the buried weak layers. Two things could change that. 1. A wind event. One quick way to get a slab is to build one with some dry snow and moderate winds. That’s why we have wind affected areas on our mind when we travel to areas with thinner snowpacks. 2. A big storm. While areas like the Wenatchee mountains have seen their fair share of snow this season, these areas haven’t seen a big loading event. How would this weak snowpack handle a big storm? It’s hard to say at the moment. Just remember, if you go to mountainous areas around Twisp, the Wenatchee Mountains, or the East-South zone, you may encounter snowpacks with lingering persistent weak layers.

A shovel tilt test highlights weak snow interfaces in a very shallow east-side snowpack. Photo: Josh Hirshberg

The danger is real:

Even though the snowpack is strong and the avalanche hazard is generally low, there are other risks in the mountains that may pose a very real danger to backcountry travelers. The one we keep hearing the most about is very firm and slick surfaces. You are most likely to find icy surfaces in locations that did not receive much snow during this recent storm. When conditions are like this, it’s tough to gain traction, and any slip may result in a long uncontrolled fall.

Icy snow surfaces have been making travel conditions difficult, and sometimes dangerous. This firm, slick layer is buried below the most recent snow in many locations. Photo: Dallas Glass

What’s next?:

Given the strength of the snowpack, it will likely take a larger storm to ramp the avalanche danger back up. When will that storm arrive? We’ll keep watching the weather patterns and let you know. Make sure to check the latest weather and avalanche forecast before you head into the mountains.

-NWAC team

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