Mozcast: Weather Report For Google Algorithm Changes

Google is always making changes to their algorithms, whether they are officially announced to the public or kept under wraps. The main algorithm changes, Panda and Penguin, have hit some websites pretty hard and negatively impacted rankings. These updates have had multiple versions released or data refreshes where the update was run again, and these updates usually are claimed to affect around 1% of search rankings (i.e. Panda 3.9). While this percentage may not seem like much, it is a significant number given the immense number of websites and searches out there. Unless you are extremely active and knowledgeable in search engine optimization (SEO) it is difficult to monitor changes in Google’s algorithms. If you are not one who is deeply immersed in SEO, have no fear, as SEOmoz recently released Mozcast. Mozcast is a daily weather report based upon the changes or “turbulence” for Google search engine rankings to indicate algorithm changes.

Google makes hundreds of changes to their algorithm each year (516 changes in 2010) indicating that being aware of when these changes are occurring can be extremely beneficial to anyone involved in internet marketing. As a top internet marketing company we stay on top of Google updates and continuously monitor rankings, but Mozcast seems to be a great tool for anyone who may not be as up to date with the Google algorithm changes.

What Does The Weather Report Mean?

The daily weather report is based on the changes noticed in search engine rankings over the past 24 hours. The hotter and stormier the weather report, the more Google’s algorithm and search engine rankings have changed in the past 24 hours. An average day is roughly around 70°F so weather reports above 70°F indicate higher than average changes and lower temperatures indicate a lower than average amount of changes. Depicting the changes as a weather report is more for fun, but it also makes it extremely easy for anyone to understand the amount of changes occurring within the past 24 hours. The temperature in the weather report is converted into an icon for one of the five following severity levels:

The weather severity icon is based on the temperature, so stormier icons such as rain will coincide with higher temperatures (more change) and sunnier icons will typically coincide with lower temperatures and less change.  The weather severity icons are considered to be a at-a-glance view while the actual temperature is more of a refined view. The temperature is calculated based on the metrics that measure change which we will explain later in this post.

Current, 5 Day, & 30 Day Reports

Upon viewing Mozcast’s page you will see the current weather report in the center of the page with a large icon depicting the type of weather and temperature.  The current weather report is actually for the previous day because the report is generated based on the previous 24 hour history of Google algorithm changes. To the left of that you will notice a sidebar weather report on the left, which gives the weather reports for the previous 5 days. This gives the weather icon, temperature, day of the week, and date for easy reference. Also below the main weather report the page shows a bar graph that gives the weather report for the past 30 days. This only shows the temperature, but the temperature is really the most important measure of algorithm changes.

How Does It Work?

Every 24 hours the creators track a set of 1,000 hand-picked keywords that are deliberately chosen to be depersonalized, delocalized, and evenly split across 5 “bins” of search volume. The results are tracked from the same location and same time everyday to keep the system as controlled and consistent in execution as possible.  Then for every keyword the creators pull the top 10 Google organic results and compare them to the results from the previous day to calculate the rate of change or “delta.” From there two metrics are used: Delta 10 and Delta 100.

What Are These Metrics?


Delta100 is the first metric used in the temperature calculation process. Delta100 measures the changes in top 10 rankings for any two days. The Delta100 metric gives a number ranging from 0 to 100. The number of the metric is calculated based on these rules:

+0 if the rankings for the keyword stay the same.

+|#| if the ranking  moves within the top 10.

+10 if the ranking drops out of the top 10.

When a ranking moves the “#” refers to the number of spots it moved. To make this easier to understand, if a URL moved from #1 to #5 then the “#” is +3 which gets added to the Delta 100 for the keyword. This is calculated for all the URLs in the search results for the given keyword to get the Delta100 for the keyword. Delta 100 is calculated for all 1,000 keywords and is used to calculate Delta 10.


Of the two metrics used to determine the weather report, Delta10 is used to calculate the temperature of the weather. Delta10 is essentially the rate of change across the entire top 10 results. Delta10 is calculated by taking the square root of Delta100 for each keyword. Delta 10 is based on a scale of 0 to 10 respectively, because Delta100 is on a scale of 0 to 100. Then the creators take an average (non-weighted) of all Delta10 figures to use in the calculation for the temperature. At this point, Delta10 is multiplied by a fixed multiplier to calculate the temperature (numerically in °F) of the given days weather report. The fixed multiplier is currently 28.0, but this could change as the tool is still in its initial stages and will likely receive some revisions.

Wrap Up

Mozcast is updated around 7:30am PST and also includes Events and News pages. The News page will showcase the product updates to Mozcast and the Events page includes a list of recent algorithm changes and their respective weather scores.

Now that SEOmoz has provided everyone with a valuable reference point, its important for everyone involved in this field to be aware of it and to utilize it. Although it will not tell you what changed in the algorithm, it is a good indicator of when Google updates are taking place. So go check out Mozcast and let us know what you think.

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