St. Helena Weather

Napa Valley Weather Notes

St. Helena sits at the heart of the Napa Valley floor, sheltered by the Mayacamas Mountains to the west and the Vaca Range to the east. The valley's fog-channeling geography creates a natural air-conditioning effect — cool Pacific fog rolls in from San Pablo Bay each evening, burning off by mid-morning. Summer afternoons typically reach the 90s°F while winter lows can dip into the low 30s. The peak growing season runs May through October, and frost risk is highest December through February.