Moisture is a painter's worst enemy. Waterlogged wood siding or concrete foundations will cause paint to bubble and crack only months after a fresh application. Save yourself the frustration (and cost) of repainting by waiting until all surfaces are moisture-free.
If you live in a region with long, snowy winters and wet springs, wait until at least June before starting an exterior paint project. If you live in a hot and humid region, plan on the cooler, drier weather of fall. Professional painters carry moisture meters and won't lay a brush on a piece of wood with moisture content higher than 12 percent [source: Lernley].
You can buy a meter for as little as $20 — or just keep tabs on the weather. Wait until the forecast calls for clear skies and warm nights for at least the next week. Rain can wash away fresh latex paint, and temperatures below 50 degrees Fahrenheit (10 degrees Celsius) can make it harder for paint to adhere to the surface and cure properly [source: Benjamin Moore].