Mostly commuted year round for the last 20 years, though there have been occasional exceptions. My commute has typically been embarrassingly short - because I buy houses close to work.
When I lived in Indiana, summer commuting was about humidity and winter commuting was about re-frozen slush.
When I lived in west Texas, commuting was dominated by heat and, well, by west Texans who had clearly never seen a gainfully employed human using a bike for transportation.
Now here in the PNW, chilly and drizzly describes much of September through May. I wear wool knickers re-made from Goodwill dress slacks those months. Hand-crafting knickers from Goodwill slacks is the second most Portland thing I've ever done.
Cheers