Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Phnom Penh to Oregon as you normally would.
In terms of precipitation, rainfall in Oregon ranges from 0.7 - 5.6 inches per month. November is typically the wettest month, when rainfall can reach 5.6 in. July is typically the driest time to visit Oregon when rainfall is around 0.7 in.
If weather is an important factor for your trip to Oregon, 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 69.8 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 41.0 F).