MozCast is a free daily index, published by the search software company Moz, that measures how much Google's organic search results changed from one day to the next and expresses the answer as a temperature in degrees Fahrenheit. A quiet day reads in the high 60s or low 70s. A day on which rankings move sharply across thousands of queries reads far hotter. The tool exists because Google changes its ranking systems constantly but confirms only a fraction of those changes, and site owners watching their own traffic cannot tell whether a fall is theirs alone or part of a wider shift. MozCast offers a shared reference point: one number, calculated the same way every day, on the same set of keywords. Each daily figure comes with a weather icon, from sunshine to storms.

How the temperature is calculated

The method rests on a controlled sample rather than on any data supplied by Google. At launch in 2012, MozCast tracked 1,000 hand-picked keywords, according to Search Engine Roundtable, which described the methodology at the time. Every 24 hours, a crawler records the top 10 organic results for each keyword, querying at roughly the same time each day from the same location. Keywords with obvious local intent were excluded, and the set was spread evenly across five "bins" of search volume, so that neither head terms nor long-tail queries would dominate.

Each keyword's top 10 is then compared with the previous day's top 10. The difference is a change rate, which Moz calls a "delta". Two versions were defined at launch, Delta100 and Delta10, both measuring movement within the first page. The Delta10 values are averaged across all keywords and multiplied by a fixed constant, which was 28.0 in 2012, to produce the temperature. The constant has no meaning of its own. It was chosen so that an average day lands at around 70°F, a figure that reads as mild to anyone used to a US weather forecast.

A worked example shows the arithmetic. If the average Delta10 across the sample on a given day were 2.5, the temperature would be 2.5 multiplied by 28.0, or 70°F. If heavy reshuffling pushed the average to 4.0, the reading would be 112°F. The example is illustrative; Moz has not published day-level delta values alongside its temperatures, and the precise delta formula was not set out in the sources reviewed for this article.

The sample has since grown. Descriptions published by third parties, including an industry guide by Reputation X updated in September 2026, put it at about 10,000 keywords measured in five major US cities. Moz's own methodology page could not be retrieved for this article, so the current keyword count and city list are attributed to those secondary descriptions rather than confirmed with the company.

Readings are published a day in arrears, alongside a 30-day chart and a hand-annotated list of significant events.

What a temperature means

Moz's original guidance tied a reading of 90°F or higher to a likely major algorithm change, according to Search Engine Land's 2012 report. Fifteen months of data analysed in a 2013 post on the Moz blog, by community contributor Ben Morel using figures supplied by Moz, gave a mean of 68.10°F and a standard deviation of 10.68°F. On those numbers, about 90% of days fell between 46°F and 90°F.

The distribution is lopsided. It showed positive skew, meaning more unusually hot days than unusually cool ones, and a normal distribution would have predicted about one day above 100°F per year. The data contained 14, most of them in June 2013.

Beyond the temperature

MozCast publishes companion metrics drawn from the same daily crawl. They include domain diversity, the share of unique domains in the top 10 results; the Big 10, the share of results held by the ten most prominent domains; the influence of exact-match and partial-match domains (EMDs and PMDs), whose names contain the query; and a history of SERP features, the non-standard elements such as featured snippets and video carousels that sit on a results page.

Origin and evolution

MozCast was built by Peter J. Meyers, a cognitive psychologist known in the industry as Dr. Pete, who joined SEOmoz in 2012 and later held the title of marketing scientist. He tested the tool privately with Barry Schwartz of Search Engine Roundtable for several months before its public release on August 1, 2012.

Schwartz had for years reported Google updates by reading webmaster forums. "I always took a human approach to watching the forums, seeing the complaints," he wrote at the launch, describing MozCast as a test of "my human findings and his algorithmic findings." The idea was not new: SERPmetrics already ran a similar tracker, both outlets noted.

SEOmoz, founded in Seattle in 2004 by Rand Fishkin and Gillian Muessig, renamed itself Moz in 2013. On June 4, 2021, Moz was acquired by iContact, a unit of J2 Global, the company later renamed Ziff Davis. MozCast continued under the new ownership and was still publishing daily charts in 2026.

Why it matters to marketers

Google confirms core updates, and since December 14, 2022 has logged them on its Search Status Dashboard. It does not explain the many unconfirmed swings in between. That gap is where MozCast and its peers operate. An organic traffic drop on a day MozCast reads 70°F points to a site-specific cause, such as a technical fault or a lost link. The same drop on a 110°F day points to something industry-wide.

The tool also serves as corroboration. PPC Land's reporting on ranking turbulence routinely lists MozCast among a dozen or more trackers. It appeared in coverage of spikes from April 21 to 23, 2025, of fluctuations from June 28, 2025 ahead of Google's confirmation of the June 2025 core update, and of the December 2025 core update, which ran 18 days from December 11 to December 29. When several independent instruments rise together, an unannounced change becomes harder to dismiss.

Limitations and criticisms

A temperature is a measure of movement, not of cause. MozCast cannot say which sites gained or lost, why, or whether any particular domain was affected. A 2018 comparison by the UK agency Salience criticised the weather metaphor for lacking context about what a "good" temperature is.

The sample is narrow by design. It covers only the top 10 positions, only US results and only the queries Moz chose. A change confined to page two, to local results or to markets outside the US can pass unnoticed. Moz itself has acknowledged data quality issues: Meyers told the 2013 analyst, "I don't always correct metrics data past 90 days, so sometimes there are issues with that data on the past," and a counting error for YouTube results left some 2012 diversity figures unreliable.

The hardest dispute concerns spikes with no confirmed cause. On June 26, 2013, MozCast recorded 113°F, its hottest reading to that point, and 120°F followed later that week. Other trackers, SERPs.com and SERP Metrics, showed normal readings for the same Tuesday, and Schwartz reported no matching surge in forum complaints, according to Search Engine Roundtable. Meyers said he needed more time to give a definitive answer. The episode illustrated a recurring problem: a single tracker's sample can move for reasons that have little to do with what most sites experience.

Interpretation has also become harder. SEO consultant Gagan Ghotra's analysis, covered by PPC Land in January 2026, found confirmed Google updates fell from 10 a year in 2021 and 2022 to four in 2025, while volatility rose. More unannounced movement means more hot readings without an official explanation. Meyers acknowledged the difficulty after the August 2023 core update, which MozCast recorded peaking at around 122°F on August 23 and 24: "Core Updates are already multi-signal and a bit mysterious, and this one is even harder to disentangle than most," he told Search Engine Land.

Finally, every tracker that scrapes Google depends on Google tolerating the scraping. When Google removed the num=100 parameter on September 14, 2025, the cost of deep rank tracking rose across the industry. MozCast's top 10 design means it never depended on 100-result pages, but it shares the broader exposure to anti-scraping measures.

Semrush Sensor. A rival volatility index that scores daily change on a 0 to 10 scale, with bands from low (0 to 2) to very high (8 to 10), according to Semrush. Unlike MozCast, it reports by industry category, device and several countries. The two often disagree in magnitude.

Rank tracker. Software that records a specific site's positions for its own chosen keywords. MozCast is built on the same crawling technique but reports on the search engine as a whole, not on any one site.

Visibility Index. A score, popularised by Sistrix, estimating how prominent a single domain is across a large keyword set. A Visibility Index tracks winners and losers; MozCast tracks how much the results moved overall, without naming either.

Search Status Dashboard. Google's own log of confirmed ranking updates and incidents. It records what Google says happened; MozCast records what the results did, confirmed or not.

Recent developments

MozCast remained part of the standard toolkit during the turbulent run of 2025 and 2026. It was among at least 13 services that registered higher-than-usual volatility around October 28, 2025. It also appeared alongside Semrush, Sistrix, Accuranker and Algoroo in reporting on the sharp volatility of May 13 and 14, 2026, which came with a rise in deindexed pages and no confirmed update. Google's March 2026 core update launched on March 27 and its May 2026 core update was announced on May 21, finishing around June 2, and Search Engine Roundtable published MozCast charts during both rollouts. MozCast showed the results moving; explaining why remained the task of everyone else.

Timeline

  • 2004: Rand Fishkin and Gillian Muessig found SEOmoz in Seattle.
  • 2012: Peter J. Meyers (Dr. Pete) joins SEOmoz; MozCast tracking data begins in spring.
  • August 1, 2012: MozCast launches publicly, tracking 1,000 keywords with an average day of about 70°F.
  • 2013: SEOmoz renames itself Moz.
  • June 26, 2013: MozCast records 113°F, its hottest day to that point, later followed by 120°F; other trackers show normal readings.
  • December 2013: A Moz blog analysis of 15 months of data reports a mean temperature of 68.10°F.
  • June 4, 2021: Moz is acquired by iContact, a unit of J2 Global (later Ziff Davis).
  • December 14, 2022: Google opens the Search Status Dashboard.
  • August 23 to 24, 2023: MozCast peaks at around 122°F during the August 2023 core update.
  • September 14, 2025: Google removes the num=100 results parameter, raising rank-tracking costs.
  • December 11 to 29, 2025: Google's December 2025 core update rolls out.
  • March 27, 2026: Google launches the March 2026 core update.
  • May 13 to 14, 2026: MozCast and other trackers record sharp unconfirmed volatility.
  • May 21 to around June 2, 2026: Google's May 2026 core update rolls out.

Summary

Who: Moz, the Seattle search software company owned by Ziff Davis since 2021, publishes MozCast; it was built by Peter J. Meyers. SEO teams, publishers and trade press use it, and Google plays no part in it.

What: A daily index of how much Google's top 10 organic results changed from the previous day across a fixed keyword sample, shown as a temperature in which about 70°F is a normal day.

When: Launched publicly on August 1, 2012, with data from spring 2012, and still published daily as of October 2026.

Where: Google's US organic results, sampled from a fixed location set (five US cities, according to third-party descriptions), published free on Moz's website.

Why: Google confirms only some ranking changes; MozCast gives the industry a consistent, independent reading of turbulence so that site owners can judge whether a traffic change is theirs alone or part of a broader shift.