My minibadger likes to make snowflakes by cutting a folded up a sheet of paper with scissors (and dropping the bits all over the kitchen floor.) I like snowflakes made by taking a mass of moist air and chilling it to make ice crystals then sticking these crystals together as they fall to the ground.
Yesterday, I heard the weather chap on the radio say that the snow today would be “light and no good for snowballs”. I thought this sounded fishy, as I’ve spent the last part of the week looking at the weather models trying to decide whether we’ll be getting rain or sleet overnight. Surely if the snow is borderline turning to rain/sleet it’s going to be wet/sticky “snowballs/snowman” snow?
Not being a snow expert I revised some snowflake science. Looking at the temperatures associated with the weather front expected over the UK today, we’ll have a temperature ascent warm enough to make the ice crystals “sticky”. This means that they will coalesce more as they fall to earth, making larger flakes – better for snowballs.
Conversely if the temperatures are too low, then the crystals don’t stick together so much, and you end up with dry powdery snow, which is less dense than average.
Speaking of density, the ratio of water content to snow indicates whether you have powdery snow or wetter snowball/snowman snow. An average is around 10:1 snow to water. So 10cm of snow comes from 1cm of water. Wet snow can have a ratio of 5:1, (1cm water -> 5cm snow) whereas dry powdery snow will have a higher ratio (e.g. 1cm water -> 20cm snow). The weather model was showing around 12mm of rain falling over Oxford tonight, but giving a snow cover of 80mm. This ratio of 7:1 suggests wettish snow. Once the snow has fallen, overnight temperatures may mess things up, but I reckon keep your carrots at the ready for tomorrow morning.
Incidentally, I wondered whether the myth that Eskimos have hundreds of words for snow is true. Wikipedia says it isn’t.
Enjoy the snow if you can. Let me know if you get any snow, and if it’s powder or slush, or something in between.
WB