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- will increase snow depth according to the proportion of snow in the mix - acting as snow falling onto snow as given above.
- will increase snow density according to the rain in the mix - acting as rain falling onto snow as given above.
- commonly snow depth/mass on the ground increases too much when ice pellets and/or sleet are falling (i.e. melting of the evolving snowpack is underdone)
Ice crystal fog or diamond dust
When very low temperatures are forecast, polar regions, far northern Russia, Antarctica) models can sometimes show some precipitation. No supercooled liquid water possible in the atmosphere at these low temperatures but ice-crystal fog/cloud or "diamond dust" (ice crystals forming in what sometimes looks like clear sky) may occur. This could be an additional hazard to human work or aviation. The air can become supersaturated with respect to ice, and ice crystals nucleate and grow. This process is represented in the model but the model output it is just categorised as "snow" precipitation at the surface on chart output and it will have some associated "cloud fraction".
Fig9.7-4: Meteogram for a location in Antarctica, DT 00UTC 8 Feb 2026. On the forecast for Mon 9 Feb temperatures are around -52C, small amounts of precipitation are shown and almost full cover of cloud. This could be indicative of ice-crystal fog/cloud or diamond dust.
Snow forecast information
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Ice
- Thin sea-ice or lake-ice covered by thin snow grows or melts much faster than does thick ice with deep snow.
Additional sources of information
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