By Ross Woods

On Monday morning I posted an album of photos of the snow near my house on my Facebook page, including shots like this one:


My son, who likes to tease me about spending too much time working, then asked me ‘what are your predictions for gutter flow rates due to snow melt in the coming days …’

This got me thinking about how to find out quickly how much snow there was around Christchurch, and then I had the idea of using networks on Facebook and at NIWA to get some crowd-sourced data on snow depth. At noon on Monday I created an open Facebook group called ‘How Deep is the Snow at Your Place? (July 2011, NZ)’, and offered some guidance on how many measurements to take (ten) and how to choose a good spot (away from fences, buildings, valleys). I circulated the same message at NIWA in Christchurch. Most of my replies came in within the first 3 hours.

I got 44 responses from Facebook and NIWA, from as far north as Wellington (‘no snow’) and as far south as Dunedin. I also got a nice report from an experienced hydrologist who had driven from Picton back to Christchurch, and taken note of how deep the snow was at quite a few locations. The most common snow depths were in the range 10-15 cm, and the statistical distribution of snow depths looks like this:


Where was the deepest snow? I couldn’t see any particular pattern in the snow depth data: there’s a map of the data points on the Google Maps page I quickly put together. The page is still under development — the colour of the placemarkers has been giving me trouble but I’ve nearly got it.

In the meantime, the Terra satellite was capturing some nice imagery on where the snow was, and NIWA staff were out doing a scientific survey of snow depth and density — more of that to come later…