Which report includes information on significant changes in weather conditions?

The correct answer is the report that focuses on significant changes in weather conditions: the SPECI report. SPECI, which stands for Special Report, is issued when there are notable changes in weather elements that are significant enough to warrant immediate update outside of the regular METAR reporting schedule. These changes can include sudden shifts in visibility, weather phenomena, or significant variations in wind patterns, among others.

Unlike the TAF, which is a forecast statement for future weather conditions, the METAR report provides routine hourly observations and does not account for significant updates that fall outside of the regular schedule. The AWOS, which stands for Automated Weather Observing System, provides automated weather data and might transmit routine observations, but it is not specifically focused on updates regarding significant weather changes. Thus, the SPECI report serves as the essential tool for indicating important and immediate weather changes, making it the best answer in this scenario.