Is it safe to store an extension cord outside under a carport?
Water, extreme temperature fluctuations (+-30&deg;), and direct sun exposure can all damage the insulation of the cord. If you live where wind driven sand/snow is a thing, you might have problems. The contacts can be corroded if exposed to water, and very moist air (especially if it's moist salty air).

Inspect the cord for brittle, cracked, torn, or damaged insulation before each use. Inspect the contacts for corrosion before each use.