How would the visibility report be coded for "the prevailing visibility is two and a half statute miles"?

The visibility report for "the prevailing visibility is two and a half statute miles" is coded as 2 1/2SM. This coding accurately reflects the prevailing visibility in a standard format used in aviation weather reports.

In aviation weather reporting, visibility is expressed in statute miles, and when fractional miles are included, they are represented as a decimal. However, it is also permissible to use the fraction as clear textual representation, especially in contexts where fractional visibility needs to be explicitly indicated. Therefore, the correct choice provides both clarity and adherence to the required reporting standards.

Other options might not accurately convey the intended visibility. For example, using "12SM" suggests a visibility of 12 statute miles, which does not match the specified condition of two and a half statute miles. Similarly, "4SM" overstates the visibility, while the choice indicating "2SM; RMK VIS S 1 1/2" would suggest reduced visibility represented through a remark, which also misrepresents the prevailing visibility condition described in the question. Thus, the choice that reflects the actual visibility accurately and in a commonly understood format is the most appropriate.