In Central Virginia, the best windows for exterior painting are usually late spring and early fall. Days are warm, nights don't drop too low, and the humidity is more manageable than in July and August.
Most exterior paints want surface and air temperatures above about 50°F while the paint cures, and they don't like dew settling on a fresh coat. That's why we start on sunny sides later in the morning, after the dew burns off, and wrap up early enough that the paint can skin over before evening.
Weather is only half of it. Paint fails at the prep: on chalky siding that wasn't washed, on loose paint that wasn't scraped, at gaps where old caulk cracked. We power wash first, let the house dry, scrape and sand, recaulk, and spot-prime bare wood before any finish coat goes on.
If your paint is peeling, your trim has soft spots, or the siding leaves chalk on your hand, it's time to get a quote. Fixing wood rot while it's small costs a lot less than replacing whole boards later.