What are the last three digits of the '5 group' in the METAR report used to indicate?

The last three digits of the '5 group' in the METAR report specifically indicate the pressure change in tenths of millibars (mb) over the past three hours. This is crucial for understanding how the atmospheric pressure is shifting, which can provide insight into weather patterns, such as the approach of a weather front or a storm system.

Each digit in this group represents a specific measure of pressure change, where positive changes are indicated by a leading zero or a "+" sign, and negative changes come with a minus sign. This information helps aviators and meteorologists assess stability or volatility in the current weather conditions, aiding in flight planning and safety.

The other options do not accurately describe what the last three digits of the '5 group' represent. For example, maximum and minimum temperatures over the past hours would be indicated elsewhere in the METAR report, as well as current weather conditions, which would be given in a different format altogether. Thus, the understanding of pressure change is vital for accurate interpretation of METAR reports.