Convective rainbands can form parallel mountains on their windward side. This is due to lee waves triggered by hills just upstream of the cloud's formation. Their spacing is normally to apart. When rainbands near frontal zones get close to steep mountains, a low-level barrier jet stream forms parallel to and just before the mountain ridge. This slows down the frontal rainband just before the mountain barrier. If enough moisture is present, sea breeze and land breeze fronts can form convective rainbands. Sea breeze front thunderstorm lines can become strong enough to hide the location of an approaching cold front by evening. The edge of ocean currents can cause thunderstorm bands due to heat differences where they meet. Downwind of islands, rainbands can form when low level winds meet downwind of the island edges. Offshore California, this has been noted in the wake of cold fronts.