How many minutes prior to the scheduled observation time can an observation be started?

The correct answer signifies that an observation can be initiated a maximum of 15 minutes before the scheduled observation time. This timeframe is established to ensure that the weather data being collected is as relevant and accurate as possible for the scheduled reporting period. By allowing a 15-minute window, weather observers can capture any transient weather phenomena that may occur just prior to the official observation time, thereby improving the reliability of the data.

Starting observations too far in advance may lead to discrepancies as conditions can change rapidly, and observations may no longer represent the weather at the official time. Therefore, adhering to the 15-minute limit strikes a balance between capturing current conditions and ensuring the accuracy and relevance of the data reported.

This practice is vital for maintaining consistency and standardization in weather reporting, which is crucial for flight safety and operational planning in aviation.