Let's start by saying "do not install your new roof is temps are not above 40 degrees for 48 hours. That is with direct sunlight!"
The warmth of sunlight seals the mastic, sealant (glue) strip the shingle manufacturer places on the lower underside edge of composition shingles. Once sealed, this helps protect your roof from having shingles flapping about and blowing off in moderate to high winds. If the weather is cold or cloudy when your roof is being installed, additional time will be necessary to seal down the lower edge of these shingles. Until then, it is not unusual for the lower edge of many of the shingles to not lie down smoothly, giving your roof a ‘ruffled’ appearance. This is typical and will correct itself after several weeks of sunny, warm days.