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Dominik's avatar

Great article! Does this also apply to other variables like wind speed or wind direction, where there's no such a simple gradient with height? I guess it's better to take the nearest grid cell for these to get the most accurate values?

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open-meteo's avatar

Hi. No corrections are applied to wind speed or direction. This would require more complex fluid dynamics calculations which is by itself a highly specialised field. For consistency, the same grid-cell is used as for temperature or any other weather variable.

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Simon Horton's avatar

So just to clarify, is elevation downscaling applied only to temperature variables? Does that mean precipitation phases like snowfall and rain won’t be adjusted for temperature changes? What about relative humidity, since it’s easy to adjust based on temperature?

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Colin Noakes's avatar

Hi Simon - I'm guessing you might have got here from my website alpineconditions.com (which uses OpenMeteo).

Not to speak to OpenMeteo, I did a bit of digging around their source code and they _do_ a bunch of corrections on surface variables such as humidity depending on the elevation that gets fed into the system - either from the Digital Elevation Model or requested: https://github.com/open-meteo/open-meteo/blob/main/Sources/App/Helper/Meteorology.swift

FWIW - if you're looking at my website - I'm actually doing a few further tweaks to the data - one of which is the snow/rain is modified depending on surface temperatue. I'm using 2 degrees C as the cut off for snow. If it's warmer than that, it'll be marked as rain on alpineconditions.

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Simon Horton's avatar

Thanks for sharing the source code, Colin. I build tools for Canadian avalanche forecasters and recently came across your website, which I really like. I’ve done quite a bit of weather data manipulation to better capture alpine conditions over the years, so it’s great to see others working on this challenge too.

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