Snow science seems to be in vogue and nothing wrong with that. But - most folk are not avalanche forecasters just Joe average trying to make good decisions. I like to simplify it when discussing so here’s a white board session based on a picture taken on an avy course I ran some time ago when the PowerPoint projector failed and I had to cuff it. A good whiteboard session is good as an instructor as you need to know your subject and cant hide behind pictures:
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| Mountaineers are seldom "searchable" Above "The Gate" below Summit Gully Glencoe Spot Probe Finds x 2 Fatal 😢 |
- The avalanche forecast is an area forecast. The local risk may be different + or –
- Read the forecast and its nuances, snow pack history and snow profile – and the blog. They have done 80% of the work for you. You decide the rest
- Terrain choice is a big deal, Angle, Aspect and Altitude, Complexity, Commitment and Consequences
- Water becomes ice or something along a continuum
- Snow flakes have branches which break up if transported by the wind
- More wind more break up, denser snow pack i.e Slab
- Graupel is not hail which is a laminate, but it is a ball of softish ice. Graupel are ball bearings with similar effects with new snow laying on top. They eddy into rock features causing local weakness. Rocks can be Islands of safety or a landmine.
- The deeper you go down the snow pack the less cold it gets until at ground level its zero or just above. Mice shrews and invertebrates live there.
- Water vapour rises through the snowpack.
- Crystals can grow/regrow in cold conditions either on the surface as hoar or within the snowpack as hoar/crystal regrowth.
- Early season shallow snowpacks can be just as lethal as big deep snowpacks as water vapour causes surface hoar which if snowed on become lethal, graupel can be trapped around prominent rocks causing trigger points, or crystal re growth/faceting can occur and get buried. Shallow is just as lethal as deep.
- Avalanche forecasters measure the snow temperature every 10cm. If the temperature is greater than 1c in 10cm going up the snowpack then the snowpack is getting weaker. Less than 1c in 10cm then overtime the snow pack will eventually get stronger, Strong gradients grow facets, weak gradients make rounds.
- In rain, thaw and warmer weather crystals round off sometimes joining to each other
- Wet snow is Water logged snow and can flow like a concrete river down gullies, corries and obvious slide paths. Beware spring thaws or after heavy rain.
- Wind blown slab snow shears or collapses on a layer underneath and just like rice crispie's there's a snap, crackle and pop
- Whump is the sound of air escape from under the slab, the snap. If it doesn’t pop go buy a lottery ticket as your lucks in.
- Windslab most often requires a trigger. You are the trigger and in the poop!
- Snow pits should be kept simple. The SAIS and other forecasting services in alpine countries do the heavy lifting. Snow pits and profiles are only relevant for the couple of square meters where you dig. They are good places to take stock, talk and communicate. The data might confirm what you see but also might not. Its just a hole in the snow. The armpit test is fast and repeatable but not definitive. Dig out a small hole and above cut out as deep a column as you can with a ski end, pole or shovel. Pull on it to see if the surface slab is bonded to the underlying snow pack.
- The progression of survival probability such as % survival at a given time is a statistic. You could survive a couple of hours if in the miracle headline survivor group, but more likely dead from hypoxia unless companions dig you out fast. Bear in mind ski patrollers who can get to fully buried victims in alpine resorts fast, give BLS with fast helicopter access and ALS from dedicated SAR Docs taking the victims to specialist centre's and even then victims do not survive to discharge. Your companions are your saviours.
- A shovel is an airway opening device
- If you are not searchable your fucked
- That's about it really
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