This report describes the typical weather at the Sonoma County Airport (Santa Rosa, California, United States) weather station over the course of an average year. It is based on the historical records from 1977 to 2012. Earlier records are either unavailable or unreliable.
Santa Rosa, California has a mediterranean climate with dry warm summers and mild winters. The area within 25 mi of this station is covered by forests (67%), grasslands (18%), oceans and seas (9%), and croplands (5%).
Over the course of a year, the temperature typically varies from 38°F to 84°F and is rarely below 29°F or above 94°F.
The warm season lasts from June 4 to October 9 with an average daily high temperature above 78°F. The hottest day of the year is July 10, with an average high of 84°F and low of 53°F.
The cold season lasts from November 26 to February 12 with an average daily high temperature below 60°F. The coldest day of the year is December 24, with an average low of 38°F and high of 55°F.
The length of the day varies significantly over the course of the year. The shortest day is December 21 with 9:28 hours of daylight; the longest day is June 20 with 14:52 hours of daylight.
The earliest sunrise is at 5:46am on June 15 and the latest sunset is at 8:40pm on June 25. The latest sunrise is at 7:41am on November 3 and the earliest sunset is at 4:50pm on December 6.
Daylight savings time (DST) is observed in this location during 2012, starting in the spring on March 11 and ending in the fall on November 4.
The median cloud cover ranges from 14% (mostly clear) to 79% (partly cloudy). The sky is cloudiest on January 26 and clearest on June 8. The clearer part of the year begins around March 27. The cloudier part of the year begins around November 14.
On June 8, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 56% of the time, and overcast or mostly cloudy 20% of the time.
On January 26, the cloudiest day of the year, the sky is overcast, mostly cloudy, or partly cloudy 45% of the time, and clear or mostly clear 28% of the time.
The probability that precipitation will be observed at this location varies throughout the year. Precipitation is most likely around February 2, occurring in 50% of days. Precipitation is least likely around July 18, occurring in 6% of days.
Over the entire year, the most common forms of precipitation are moderate rain and light rain.
Moderate rain is the most severe precipitation observed during 50% of those days with precipitation. It is most likely around January 6, when it is observed during 30% of all days.
Light rain is the most severe precipitation observed during 36% of those days with precipitation. It is most likely around February 15, when it is observed during 16% of all days.
During the warm season, which lasts from June 4 to October 9, there is a 10% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of light rain (41% of days with precipitation have at worst light rain), moderate rain (39%), and drizzle (15%).
During the cold season, which lasts from November 26 to February 12, there is a 48% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of moderate rain (58% of days with precipitation have at worst moderate rain), light rain (28%), and heavy rain (9%).
Either snow is exceptionally unlikely to fall at any time during the year at this location or this station does not reliably report precipitation types.
The relative humidity typically ranges from 37% (comfortable) to 98% (very humid) over the course of the year, rarely dropping below 17% (dry) and reaching as high as 100% (very humid).
The air is driest around June 15, at which time the relative humidity drops below 48% (comfortable) three days out of four; it is most humid around January 5, exceeding 97% (very humid) three days out of four.
Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
Over the course of a year, the dew point typically varies from 35°F (dry) to 58°F (comfortable) and is rarely below 25°F (dry) or above 62°F (mildy humid).
The time of the year between April 10 and November 16 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of the year typical wind speeds vary from 0 mph to 15 mph (calm to moderate breeze), rarely exceeding 20 mph (fresh breeze).
The highest average wind speed of 7 mph (light breeze) occurs around June 1, at which time the average daily maximum wind speed is 15 mph (moderate breeze).
The lowest average wind speed of 3 mph (light air) occurs around December 31, at which time the average daily maximum wind speed is 8 mph (gentle breeze).