W. Va. Code § 17C-3-7: Flashing signals.

Whenever an illuminated flashing red or yellow signal is used in a traffic sign or signal it requires obedience by vehicular traffic as follows:

(1) Flashing red (stop signal). — When a red lens is illuminated with rapid intermittent flashes, drivers of vehicles shall stop before entering the nearest crosswalk at an intersection or at a limit line when marked, or, if none, then before entering the intersection, and the right to proceed is subject to the rules applicable after making a stop at a stop sign.

(2) Flashing yellow (caution signal). — When a yellow lens is illuminated with rapid intermittent flashes, drivers of vehicles may proceed through the intersection or past the signal only with caution.

(3) Local authorities, in areas that experience low traffic times, may permit flashing signals between the hours of eleven o’clock p.m. and six o’clock a.m.