Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
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1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
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In sintesi

Expect mostly stable avalanche conditions. Large avalanches are not likely. You may be able to trigger small wind drifts in very steep, upper elevation terrain. 

Problemi valanghivi

  • Wind Slabs

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

    Monday's strong to extreme winds reshaped the snow surface in exposed terrain. Our observations indicate the wind moved snow all over the place and did not form widespread wind slabs. However, Ben saw a fairly recent wind slab avalanche yesterday on an upper elevation slope approaching 40* near Banner Summit. 

    This generation of wind slabs has had 2-3 days to stabilize, but the combination of cold temperatures and slick or faceted surfaces beneath the drifts makes me think it's still possible to trigger small slides in very steep, upper elevation terrain. In this zone, there isn't a lot of very steep terrain near and above 9000' where more wind slabs appear to have formed. While any wind slabs you trigger probably won't be large enough to bury people, they could knock you off your feet or sled and carry you somewhere you don't want to be. 

    Pay attention to how the snow surface's appearance and feel changes if you're traveling in very steep terrain. If you see cracks shooting out from your boards or skis or if you feel the snow become notably stiffer, picture what would happen to you if you triggered a small avalanche. If you're not crazy about how that story would play out, move to a gentler slope or one with less drifting. 

    ADDITIONAL DISCUSSION:  Today's warmer temperatures and intense sunshine will soften and melt the snow surface on some slopes. Yesterday, I saw a tiny wet loose avalanche that naturally released in a mid-slope cliff band in the southern Sawtooth Mtns. I don't expect much of a wet loose avalanche problem today, but it's time to start thinking about it again. If the snowpack becomes wet and sloppy, find a cooler place to play.  Consider limiting the time you spend underneath large, steep, rocky slopes directly facing the sun.

    (3/30/2021) This wind slab avalanche released near Banner Summit during the recent strong wind event.

Avalanche Discussion

TIMING IS EVERYTHING

As temperatures steadily warm beneath clear skies this week, sun-drenched slopes will likely offer better riding and skiing conditions than the boilerplate and/or crusty surfaces of the past few days. With that change, our avalanche concerns will move from alpine wind slabs to wet loose avalanches. Today should be a transition day in that I don't expect widespread, significant melting of the snow surface. But, it's coming.

In yesterday's forecast, Ben noted a dust layer within the snow that fell Monday. Also, Monday's strong, erratic winds moved dirt and dust from exposed ridgelines onto snow-covered slopes. Why does this matter? On a hot, sunny summer day, would you choose to wear a white shirt or a dark shirt if you wanted to stay cool? The light-colored shirt, because dark surfaces absorb more sunlight than light surfaces. The dirt and dust on and near the snow surface is like wearing dark clothes on a hot sunny day; it will make the snowpack absorb more sunlight and heat up/melt faster. How does this change the corn snow and wet loose avalanche situations?

  • Slopes with dirt/dust will soften more easily, or earlier in the day, than the same slopes did last week. This assumes similar overnight and daytime temperatures to those of last week, which is what weather models predict. 
  • Once soft, the darker snowpack will continue to absorb solar radiation. This could make the snowpack turn to mush more quickly and shorten the window for "perfect corn" conditions on dusty slopes.
  • Once the snowpack takes on the consistency of oatmeal, loose snow avalanches should be front and center in your mind. The dirt and dust are likely to increase the length of the "oatmeal" and possible wet loose avalanche activity periods each day, especially later this week.  

So, what's the moral of the story? The springtime snowpack is both dynamic and complicated, and the dirt and dust layer may have turned the dials up a notch. Wet loose avalanche hazard can change rapidly when the snow surface is pure white; when you add a darker surface to the equation, the frozen snow >>> corn snow >>> mush >>> wet avalanches process can further accelerate. Have fun in the sun and keep your head on a swivel as temperatures heat up this week. 

Don't miss our Digging Deeper tonight at 6:30 PM with ex-SAC forecaster and current National Avalanche Center staff member Simon Trautman speaking about wet snow and avalanches. Zoom link: https://us02web.zoom.us/j/87165998644 

PLEASE HELP US HELP YOU:  We want to learn more about how you use the Forecast and our products. Kelly Rice-McNeil (Eastern Oregon University) and Victor McNeil (Wallowa Avalanche Center) are spearheading a project to understand how you use avalanche center products and, ultimately, to improve them. While you're waiting for the corn cycle to kick into gear again, help us help you by taking 10 minutes or so to fill out a survey. Teaser: there is a little SAC-specific questioning involved - please participate and get your backcountry partners, friends, family, and clients involved! Google Forms link:  https://forms.gle/YwgEwHRnT4ucSF226  

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