Napa Weather in September

Napa Valley's climate is world-famous for wine production — warm days, cool nights, and a reliable fog pattern. Marine air from San Francisco Bay pushes into the valley through the Carquinez Strait each evening, cooling vineyards and preventing grapes from overripening. The valley orientation from south to north creates distinct climate zones from warm Napa city to cooler Calistoga.

Excellent shoulder season — warm with fewer tourists in many destinations.