BEYOND

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Sun and shadow for any date and time

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Contents
Short answer

Set a date and a time and the map shows the real position of the sun and the shadows it throws on the terrain. Play the whole day, jump to sunrise or sunset, or switch to flat light. Use it to see when a face comes into the sun, which decides wet-snow timing in spring and where cold snow keeps on shaded aspects.

What it shows

The sun and shadow tool computes the position of the sun for the date and time you set and lights the 3D terrain from there. Ridges throw real shadows into the valleys and onto the faces behind them. "Play the day" runs the sun from sunrise to sunset so you can watch a face come into the light and go back into shade. "Flat light" removes the shading so you see the shape of the terrain without it.

Spring: timing by aspect

In spring the snow surface melts and refreezes every day, and the danger moves with the sun. East faces soften first in the morning, south faces around midday, west faces in the afternoon. Riders time a spring face for the window after the crust softens and before it turns to slush; the bulletin's wet-snow problem describes exactly this.

The tool lets you check the timing for a specific face instead of the rule of thumb. A south face behind a ridge may only get the sun at eleven; an east face in a wide valley may be lit from seven. Combine it with the freezing level and the hourly sun in the weather tool.

Cold snow in the shade

In midwinter the question turns around: where does the snow stay cold? North faces and anything in the shadow of a ridge keep powder for days after a storm, and they also keep weak layers longer, which is why the bulletin so often names north-facing aspects as critical. The shadow at noon shows you which faces the sun never reaches in December and January.

What it doesn't show

  • The tool shows sun and shadow, not temperature. Air temperature, wind and cloud decide how much a slope warms; use the weather forecast for those.
  • Clouds are not in the picture. A face "in the sun" on the map can be under a cloud deck.
  • Shadows come from the terrain model, so very small features are missing, and trees do not throw shadows.
  • Sun on a slope is not a danger rating. The bulletin and the snowpack decide; the tool helps with timing.

Questions

Can I see when the sun reaches a specific slope?

Yes. Set the date, then play the day or move the time until the face lights up. Jump to sunrise and sunset to see the first and last light on a ridge.

Why does sun timing matter for avalanches?

In spring, sun softens the snow surface and wet-snow avalanches follow the sun around the compass: east in the morning, south at midday, west in the afternoon. In winter, shaded faces keep cold snow and weak layers longer. The timing on a specific face depends on the terrain around it, which is what the tool shows.

Does it account for clouds and temperature?

No. It computes the position of the sun and the shadows of the terrain for any moment. Cloud, air temperature and wind are in the weather forecast for the point; read both.

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