present weather sensor Feb 19, 2018

One thing I wish the weather station could be tracking, but currently isn’t, is whether or not it’s snowing.

Right now, I have a rain gauge that’s a “tipping bucket”, so-called because it collects rain in a tiny bucket, which tips periodically as it fills up. The rain rate is inferred from the number of bucket tips. This setup doesn’t work when it snows: snow isn’t liquid, so it doesn’t fill up the tiny bucket. You can attach a little heater to the rain gauge (here’s a classic forum-style post about how to do this), which would melt the snow and theoretically allow you to track it as liquid precipitation.

But this misses the whole point, in my opinion! The whole reason to track snow precipitation is not to measure the rate at which it’s snowing, interesting though that might be. It’s pretty simply to track the groud conditions of whether or not it’s snowing at all! e.g. ideally a sensor which emits a boolean condition IT’S SNOWING or IT’S NOT SNOWING.

Part of why this is worth knowing at all: the three main National Weather Service weather stations in New York City (where I live) are in the middle Central Park, JFK airport and LaGuardia airport. Not super representative, as NYC locations go! Plus: nearly everywhere in NYC has various exposure to different bodies of water, elevations, building heights, etc, all of which add up to local precipitation variability. I want to know whether or not it’s snowing, at any given time, at a real NYC neighborhood location!

It turns out there’s a name for a type of precipitation sensor that can distinguish between rain/snow: it’s a present weather sensor, sometimes called a disdrometer. They all measure the rate and size of falling droplets. Unlike the weather station, which was relatively cheap (~$100), most of the disdrometers are mega expensive… I’ve been trying to search Google & GitHub for disdrometers every few months, in the hope that eventually one of them “gets cheap” or someone comes up with something DIY. Here’s my February 2018 disdrometer report, in ascending order of cheapness: