Sonoma County Geography and Climate Overview Written by Gerald
Boyd Climate Sonoma County is a diverse landscape for grape
growing that, climatically, is strongly influenced by maritime
variations. Cool nights and days that rarely get hot contribute
to layers of oceanic fog that creep into Sonoma’s interior
valleys through numerous spots like the Petaluma Gap. Daytime
temperatures average a comfortable 71F, with the warmest summer
days rarely topping 84F. Nighttime temperatures stay mostly in
the 40s, meaning hard frosts are a rarity, even in the spring,
the critical flowering time for grapes. In September, at the
start of the autumn grape harvest, the weather remains moderate
with little to no rainfall. Sonoma County experiences no
measurable snow or hail and normal rainfall measures between 25
and 30 inches a year. Grapes thrive in this climate and while
the county does experience the occasional temperature extreme
and hard rains, the reliably moderate diurnal swings are
tempered by coastal fog and only tra