In the U.S., METAR reports are taken once an hour between 50 minutes past the hour and the top of the (next) hour. All the observations taken within this time are considered to be for the same cycle. For example, observations taken between 1150Z and 1200Z are all considered to be 12Z observations. In reality, observations may be taken a little earlier or a little later. In addition, observations taken due to changing conditions, known as SPECI reports, are also considered to occur for a given cycle. Our rule of thumb is that all reports taken between (hh-1)45Z to hh44Z are considered to be for the hh cycle.
