When an element or phenomenon does not occur, the corresponding group, or the extension of a group, is omitted from a particular report. The groups enclosed in brackets are used in accordance with regional or national decisions. The following is the international format of the used by most countries. Each group provides a link to further details concerning observing and coding standards of the element. The format below is used by the United States and contains the modifications relating to the exceptions requested by the United States.
Most exceptions deal with the units used to report certain weather elements.
Each group provides a link to further details concerning observing and coding standards of the element. If a group is not reported, the preceding space is also not reported. When an element does not occur, or cannot be observed, the corresponding group and preceding space are omitted from that particular report.