Witnessed bright blinking white light, size of a star with smaller faint flashing red & blue lights; no noise, zig-zaging upward diaginally in short, consistent broken (z) pattern, moving fast clearing a pathway through heavy cloud coverage; no stars or moon, only light in entire sky. Very odd sighting, not the actions of an airliner, although moved horizontally at times. Disappeared after watching it for approximately 15 minutes.