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Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Pasadena to Kos as you normally would.
In terms of precipitation, rainfall in Kos ranges from 0.1 - 6.7 inches per month. January is typically the wettest month, when rainfall can reach 6.7 in. July is typically the driest time to visit Kos when rainfall is around 0.1 in.
If weather is an important factor for your trip to Kos, use this chart to help with planning. For those seeking warmer temperatures, July is the ideal time of year to visit, when temperatures reach an average of 78.8 F. Travelers looking to avoid the cold should look outside of February, when temperatures are typically at their lowest (around 50.0 F).