Friday, October 5, 2012

Summer Weather: Part 2

A quick update to my post from last time!

Last week I posted the summer numbers from my weather station analysis. At that time, the scores were (out of 100):
  • Weather Network: 66.92
  • Global Weather: 66.02
  • Weather Channel: 63.99
  • Environment Canada: 55.00
  • TimeandDate.com: 54.25
Based on the scoring system, a station could have gotten 100 if all of their temperature predictions were within three degrees of the actual weather, and the fraction of days with rain accurately matched the POP forecasts for every POP value (in increments of 10). A station could have gotten 0 only if their POP values were wildly inaccurate.

A better benchmark, though, is how well my system would have scored someone just guessing. That would potentially better demonstrate the effectiveness of weather forecasters.

Using historical data, I was able to create a "dummy" weather station that used previous years' averages to "forecast" the weather on a month-to-month basis. For example, every day in July was predicted to have a high of 23, a low of 12, and a POP of 60%.

The score obtained using this method? 38.12. In fact, the average temperature predictions were less accurate than every forecast in my model so far (just over 50% within three degrees), and the POP predictions was only better than half of the other stations' 5- or 6-day predictions*.

That's certainly encouraging! A weather station's forecasts even six days in the future are significantly better than the best educated guess you could make given historical data. So there you go - next time you criticize the meteorologist for being inaccurate, remember that actually, they're at least twice as good as you.

*: The method I use for scoring POP forecasts is perhaps objectively fair, but not very accommodating to different weather stations' reporting methods. Stations that give increments of 10% between 0 and 30 will necessarily do better than those who don't, even though a 10% POP forecast is more-or-less useless. I'm looking into ways to be a little bit more fair with this.

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