If you disregard noise/variation as an indicator of which event is cause or effect, then neither of the events you propose is clearly the cause of the other. B

If you disregard noise/variation as an indicator of which event is cause or effect, then neither of the events you propose is clearly the cause of the other. Because variation in barometer pressure is likely to be perfectly correlated with variation in storms, there's no noise/variation in either event that isn't also present in the other, so neither emerges as more likely to be the cause of the other. This strategy of identifying the causal event works only for pairs of positively correlated events whose variations/noise sometimes do not occur together, like an increase in umbrellas without an increase in rain. Can barometric pressure rise or fall due to causes other than storms? Can storms arise without being caused by a rise in pressure? I'd say maybe yes to the first (an elevation change of the meter, or a storm front that passes you very quickly but whose clouds don't pass directly overhead — maybe). But I'd say definite no to the second. If you are hit with rain from a storm, your baro pressure will drop. Thus storms cause pressure to drop, but pressure drop does not cause storms.