On a GFA, speeds of synoptic features are shown if they are moving at:

The correct answer is that speeds of synoptic features are indicated on a GFA (Graphic Area Forecast) if they are moving at 5 knots or more. This threshold is significant because synoptic features, such as fronts and low-pressure systems, are monitored closely in meteorology to understand their potential impact on weather patterns and aviation operations.

The choice to use a minimum speed of 5 knots aligns with the need for meteorological accuracy and relevance in forecasting. Features moving at this speed are considered to have a meaningful influence on weather conditions and are therefore important for pilots and meteorologists to account for. This level of detail helps in predicting the movement and development of weather systems that can affect flight operations and safety.

In contrast, speeds below 5 knots are generally considered too slow to warrant specific mention on a GFA. These slower movements may not have a significant impact on the evolving weather patterns that pilots need to anticipate. Hence, by specifying 5 knots as the threshold, the forecast remains focused on features that are more likely to cause noticeable changes in weather conditions.