I've heard the claim that the state of Kentucky produces some of the best bourbons because the state's climate has dramatic temperature changes between seasons.
Kentucky has four different seasons with an invigorating climate. Summers are hot, wet, and humid. High temperatures repeatedly cross the 95°F (35°C) mark during peak summer in July, and the heat is oppressive. Winters are cold, but short of bitter, with night temperatures below 23°F (-5°C) in January. -Weather Atlas
The idea is that the wood in the barrel expands from the heat of summer, allowing the bourbon to penetrate deeper into the oak charred barrel wood... and then shrinks again during winter, pushing the liquid out of the wood again. I assume that most bourbon is stored indoors, so I have my doubts that the climate would have much effect, if any.
Is there any proof that having an extreme climate increases quality when aging bourbon?