In a METAR/SPECI report, what do temperatures and dew points prefixed with an "M" signify?

In a METAR/SPECI report, temperatures and dew points that are prefixed with an "M" signify that the temperature or dew point is below zero degrees Celsius. The "M" stands for "minus," indicating that the recorded value is negative. For instance, if the report shows "M02," it would mean the temperature is minus two degrees Celsius.

Understanding this convention is key for interpreting weather reports, especially in regions where temperatures can drop significantly. Being able to quickly identify these readings can assist air traffic controllers and meteorologists in assessing weather conditions that may impact flight safety.