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5.2 Introduction
Unscheduled TAFs are TAFs issued at times other than the four scheduled issuance times (00, 06, 12, and 18 UTC). They are issued on an as needed basis.
The three (3) types of unscheduled terminal forecasts issued are:
Unscheduled TAFs are used to update, correct, or reinitiate previously transmitted TAF issuances. They contain the same forecast elements and use the same format as scheduled TAFs.
The primary difference between a scheduled and unsheduled TAF is some additional coding is added to the WMO header line and to the first line of text for the TAF to indicate the type of TAF issuance. Examples of each will be shown on subsequent lesson pages.