The ornamental design for a cover for a portableair blower, as shown and described.
FIG. 1 is a front elevational view of a cover for a portable air blower showing my new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a left side elevational view thereof, the right side being a mirror image;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof; and,
FIG. 6 is a reference view of the cover for a portable air blower, shown in position of use.
A broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.