The phrase "more thundery" can be replaced with a variety of synonyms depending on the context and desired tone. If you want to convey a sense of danger or imminent storminess, you might use "stormier," "more tempestuous," or "more turbulent." If you want to emphasize the noise and sound of thunder, you could use "more booming," "louder," or "more cacophonous." Alternatively, you might use "more electrifying," "more dramatic," or "more intense" to capture the excitement and energy of a thunderstorm. Whatever the context, there are many synonyms available to help you describe the qualities of a thundery atmosphere.