If visibility is reported as 1 mile, what is the code to represent this value in the reporting system?

In the Limited Aviation Weather Reporting System (LAWRS), visibility is expressed in a standardized format that ensures clarity and uniformity across reports. When visibility is reported as 1 mile, the correct representation in the reporting system is "1SM." The "SM" stands for "statute miles," which is the unit of measurement used for visibility in aviation contexts within the United States.

Using "1SM" makes it clear that the visibility is being measured in statute miles, as opposed to other possible units that might cause confusion. The other options do not adhere to the correct format: "1" lacks the unit designation, "M1" is not a recognized format for indicating miles, and "1000M" could imply a different measurement as it suggests visibility in meters rather than statute miles.

Thus, "1SM" is the appropriate and correct code to represent 1 mile of visibility in aviation weather reports.