What could there possibly be to calculate about rainfall?
Firstly, to obtain better accuracy when measuring rainfall using my 5" raingauge, rather than using a calibrated cylinder to determine the amount of rain, why not weigh the rainfall !
Now that digital scales are readily available that can weigh to 1 gram accuracy, it is a simple bit of mathematics to calculate the area the rain falls in through the 5" funnel (the usual size) and determine how many mm of rain fell.
1 mm of rainfall in a 5" funnel weighs about 12.5 g, so you can easily measure rainfall to better than 0.1 mm accuracy, which is not always easy to do using a measuring cylinder.
Secondly, I have to melt snow that lands in my raingauge to measure it (in mm) as if it had been rainfall, as well as measuring the depth of snowfall with a ruler.
This allows a comparison of snow depth against mm of equivalent rainfall.
It turns out that, approximately, 1 cm depth of snow equates to 1mm of rainfall, but this varies according to how fluffy or how compact the snow was when it fell. This 10:1 ratio of snow depth:rain equivalent can vary from 7 or 8:1 right up to 20:1
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