What type of report would be submitted if weather changes necessitate immediate reporting?

The type of report that would be submitted if there are significant weather changes requiring immediate attention is the SPECI. This report is specifically designed for situations where there are notable deviations from the existing METAR, particularly when there are changes that significantly affect the safety of flight operations. SPECI reports are used to communicate urgent updates such as the onset or cessation of weather phenomena that might impact aviation, like thunderstorms or rapid shifts in visibility.

In contrast, a METAR is a routine aviation weather report issued at regular intervals that provides a standardized weather observation for a specific location. While it relays important weather conditions, it is not issued as an immediate response to changes. AIRMET reports pertain to significant weather phenomena at lower altitudes and are used for en-route flight safety but do not serve the same immediate reporting function as a SPECI. TAFs, or Terminal Aerodrome Forecasts, are forecasts rather than observations, providing expected weather conditions over a set period and hence do not apply in immediate reporting situations.