Snowflakes 2018-02-14
It was already snowing for more than 24 hours when the first dendrites appeared. (Earlier only very tiny crystals fell with completely different shapes).
The first phase of the dendritic snowflakes were mostly small hexagons some of them with growing spikes, then very quickly this changed a lot. Much bigger flakes began to fall and they were VERY wet, with thick rime needles grown onto the plates. This phase lasted for about 2 hours then another different one came: clear, but a bit smaller dendrites fell for about 2 hours again. At the end phase the dendrites disappeared and the tiny crystals came back for s short while and by now the precipitation has almost ceased.
What does it mean? We get a lot of info from the snowflake shapes! Snowflake formation depends on the temperature, humidity and wind conditions at the cloud layer and below it. Yesterday's tiny crystals were made by a steady cold cloud layer with -8 / -10°C temp. and with only a small oversaturation. Then today the changes came: cloud layer became colder, it might have been around -10/-15°C so the plates began to fall and then as humidity rose in the cloud layer, the pplates began to grow spikes and somewhat later they became fine dendrites. Then, as the lower air layers were very humid and much warmer, the flakes got a lot of rime while they fell - I think only the intensity of the fall helped the flakes to remain frozen. Then as the huge amount of moisture of the lower layer disappeared (probably some wind intervened) the latest phase of the fall began: the dendrites became clear and most of them lacked the rime. Also their shape became a bit more complicated which means the humidity of the cloud layer became higher again.
Now only a small amount of "snowdust" is falling and the clouds are already beginning to thin.
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