Summer is in full swing in Napa Valley in July, with daytime highs ranging from the 80’s to 90’s. However, regardless of how hot it gets during the day, temperatures will nearly always cool down substantially during the evenings to the mid 50’s and even the 40’s.
In July, the average temperature in Calistoga is 73 degrees, with an average high of 92, and an average low of 53 degrees. The average rainfall in Calistoga for July is 0.03 inches. If you are planning to watch the 4th of July fireworks, you might consider bringing a light sweater, as chances are excellent that temperatures will dip to the 50’s during the evening.
July usually brings ideal sleeping weather, and it will be the rare night in when you will need to turn on air-conditioning. Moreover, if you are coming from the east or mid-west, and are used to humid summer days, you will be pleasantly surprised to learn that the summer climate in Napa Valley is extremely dry and there is little humidity.