I know that the humidity can make a difference on how your bread might turn out. Do you ever have to adjust the temp. on the oven depending on the weather? I finally found a good bread recipe that my husband really liked. I made it again and the crust was really hard. I did every thing the same. It was colder out side when I made the first one. The bread tasted really good like the other one it's just the crust was very hard. I melted butter on it just like the first one. I always put melted butter on my bread when I take it out of the oven.
A properly calibrated oven with a good thermistor will not be impacted by external temperatures or environmental factors. While, as you mentioned, humidity and environmental factors can impact cooking and baking, which influences the end product, they will not impact the temperature of the oven itself. I believe the problem is more related to the varying environmental factors, rather than the cooking temperature of the oven. As such, it might require a change in baking time, and more close monitoring the bread, rather than adjusting the temperature at which you are baking.
With that being said, I would suggest using an external oven thermometer/thermistor to confirm that there is no need for oven calibration [ie make sure that the temperature of the oven is what it was set to]. I have seen ovens begin overheating/underheating within a few days span, when the thermistor went bad. Also, it might help to make note of the ambient humidity and the results of each batch of bread you make. As you notice differences, you could take notes of what works best at differing levels of humidity, and therefore be prepared in the future to adjust according to environmental changes.