As of 2014, the book of Guinness World Records reports the largest snowflake to have been 15 inches wide and 18 inches deep, based on an eyewitness report in 1887. The report has not been proven, and scientists confirm that large snowflakes usually range from 2 to 6 inches wide.
According to a New York Times article, the manager of the physics department at the California Institute of Technology, Kenneth G. Libbrecht, confirms that it is physically possible that the report of the 15-inch wide snowflake is true. In 2013, a satellite was released enabling data weather collection, including the size of snowflakes. Scientists believe that snowflakes may begin larger but lose size as they fall to Earth.