Weather news

Snow report

The severe wintry weather is just coming to an end, but here’s an update on how much snow we got.

Now, snow depth is of course much more than the equivalent amount of rain water – snow is after all mostly air. At our location, and the typical temperatures at which snow falls here, 1mm of rain is about the same amount of water as 1cm of snow. Careful measurement by hand according to Met Office guidelines showed that on the night of Sunday 11th December, we had 15cm of snow (six inches) – about equivalent to 15mm of rain.

But our rain gauge measured just 0.4mm… Well, rain gauges, automatic or manual, don’t cope well with snow. For a start, there’s the fact that unless the gauge is heated, the snow builds up on top and doesn’t penetrate to the mechanism in the collecting cup. Rain gauges tend not to be heated because that causes other problems with potential evaporation of the precipitation before it is measured.

So our rain gauge has continued to measure small amounts of ‘rain’ during the week as the snow on top of it gradually melts. It won’t measure the whole 15mm because not only will the deeper snow cause it to settle over the sides of the collecting funnel, but also snow does evaporate directly without first melting – a process known as sublimation.

So when the dust settles, we’ll adjust our rainfall records to show just the 15mm on Sunday and none for the rest of the week.

You’ll see that in the report for December in a couple of weeks’ time!