30-year climate normals

Sonoma County Climate and Weather Averages

Hottest month — August

84.1°

average daily high. The coldest month is December, averaging a low of 36.9°F.

Sonoma County gets 33.78" of precipitation a year, and 60% of it falls in Dec, Jan, Feb.

Temperature through the year

Each bar spans the average daily low to the average daily high for that month.

Month	Avg high	Avg low	Precip
January	57.9°	37.5°	6.67"
February	61.7°	39.4°	6.67"
March	65.1°	41.4°	4.58"
April	69.0°	43.2°	2.10"
May	74.7°	46.6°	1.27"
June	81.8°	50.1°	0.31"
July	83.5°	51.7°	0.01"
August	84.1°	51.9°	0.05"
September	83.4°	49.6°	0.13"
October	77.1°	45.5°	1.65"
November	65.4°	40.1°	3.58"
December	57.5°	36.9°	6.76"

Rainfall by month

Sonoma County has a distinct wet season. 60% of the year's precipitation arrives in Dec, Jan, Feb.

January 6.67"

February 6.67"

March 4.58"

April 2.10"

May 1.27"

June 0.31"

July 0.01"

August 0.05"

September 0.13"

October 1.65"

November 3.58"

December 6.76"

Annual total 33.78"

What this climate costs you

Degree days measure how hard a building has to work to stay comfortable. They are the reason two identical houses have very different power bills, and they are the link between the weather here and what you pay every month.

Cooling degree days How much air conditioning the climate demands 410

Heating degree days How much heating the climate demands 2,904

Approximate annual cooling cost At 33.25¢/kWh, California average $136

Approximate annual electric heating cost Lower where heating is gas rather than electric $338

These are rough planning figures from degree days and the state electricity price, not a bill estimate. House size, insulation and fuel type move them a lot. See the full cost of owning a home in Sonoma County, where electricity is one line of eight.

Common questions

What is the weather like in Sonoma County?

Sonoma County averages a high of 84.1°F in August and a low of 36.9°F in December. Annual precipitation is 33.78 inches, with essentially no snow.

When is the rainy season in Sonoma County?

The wettest stretch is Dec, Jan, Feb, which accounts for 60% of the year's precipitation. That is a pronounced wet season rather than rain spread evenly through the year.

How hot does it get in Sonoma County?

The average daily high in August, the hottest month, is 84.1°F. That drives 410 cooling degree days a year, which is what your air conditioning has to work against.

Does it snow in Sonoma County?

Effectively no. Measurable snowfall is rare in Sonoma County.

Sources

Temperature, precipitation and snowfall normals — NOAA National Centers for Environmental Information, 1991–2020 Monthly Climate Normals, station SANTA ROSA SONOMA CO AP, CA US (USW00023213), 6.4 miles from the county centroid.
Heating and cooling degree days — NOAA, same station and period.
Electricity price — US Energy Information Administration, Electric Power Monthly Table 5.6.A, California residential average.
Wet-season share is the wettest three consecutive months as a percentage of annual precipitation, calculated from the monthly normals.