If you follow me on Twitter at all (and, if so, may God have mercy on your soul), you may have seen me saying things like this over the past couple of months…

…and you may have found yourself wondering “Where does he get all that wonderful data?” Like all of the best things in life – cookies, babies, belly button lint – the answer is that I made it myself. Luckily for you, I’m in a sharing mood.

Welcome to MozCast

So today, I’m pleased to announce the launch of Mozcast.com – the Google weather report. You can visit it right now, and it looks something like this:

The first thing you'll notice (besides Roger's smiling face), is yesterday's weather. The hotter and stormier the weather, the more Google's algorithm changed over the past 24 hours (a "normal" day is roughly 70°F). The weather report updates automatically each morning (about 7:30am Pacific Time currently, but that may change over time).

5-day & 30-day Reports

One every page of MozCast.com, you can view a 5-day history on the left-hand side of the screen. The home-page also provides a complete 30-day history – mouse over any day on the graph for the date and a specific temperature reading. In the near future, we'll be adding a 30-day average and may open up more historical data.

How Does It work?

There's a detailed explanation on the MozCast site, but here are the basics. We track a hand-selected set of 1,000 keywords every 24 hours. Those keywords are delocalized, depersonalized, split evenly across 5 "bins" of search volume and are tracked from roughly the same location and the same time every day. Our goal has been to keep the system as controlled as possible.

For each keyword, we store the top 10 Google organic results, and then we compare those results to the previous day. We calculate a metric called "Delta10", which is essentially the rate of change across the entire top 10. Then we take the average of all Delta10s (which ranges from 1-10) to measure the daily flux. We multiply that by a fixed value (currently, 28.0), and that becomes the day's temperature on MozCast.

Each temperature is also converted into one of five weather states: sunny, partly cloudy, cloudy, rainy, or stormy. These are completely dependent on the temperature - think of it as the quick view. The stormier it is, the more rankings changed. If it's really hot and stormy, odds are good that something big changed in the algorithm. You can see more in the launch presentation from Mozcon below:

Get Twitter Updates

We've also created a new Twitter account @mozcast - stay tuned there for daily weather reports, feature updates, and occasional deep dives into unusual events. If you're at Mozcon, I'll be at the Garage party tonight and around all day Friday, so please feel free to stop me and ask questions about MozCast. I hope it keeps you out of the rain, even here in Seattle.