Making Fudge or Candy While it is Raining or Snowing
It's not an old wives tale; it's actually true to a point. I can't say it better than Exploratorium, Science of Cooking

Can weather affect candy making?
Oddly enough, it can. Cooking candy syrup to the desired temperature means achieving a certain ratio of sugar to moisture in the candy. On a humid day, once the candy has cooled to the point where it is no longer evaporating moisture into the air, it can actually start reabsorbing moisture from the air. This can make the resulting candy softer than it is supposed to be.
That’s why dry days are recommended for candy making, although the effects of humidity can be somewhat counterbalanced by cooking the candy to the upper end of the appropriate temperature stage.
Cool weather is also recommended for candy making, because—generally—the faster candy cools, the less chance it has to form unwanted crystals.
At The Fudge House on Fisherman’s Wharf in San Francisco, they like to make fudge on cool days for another reason: According to owner and candy maker Tom Lowe, people eat more fudge when it’s cooler.

Huge commercial operations are in humidity controlled buildings, but you can get home dehumidifiers too. Perhaps one in the kitchen could help.