The ornamental design for a frontcowl for a vehicle, as shown and described.
FIG. 1 is a top front right perspective view of a front cowl for a vehicle, showing my new design, with the top front left perspective view being a mirror image thereof;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevation view thereof, with the right side elevation view being a mirror image thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The broken lines shown in the drawings depict portions of the front cowl for a vehicle that form no part of the claimed design.