Climate - Santa Rosa (California)

The climate of Santa Rosa is mild oceanic, with mild, rainy winters and warm, sunny summers, but with cool nights.
The city is located 80 km (50 mi) northwest of San Francisco, and approximately 30 km (20 mi) away from the ocean. We are near the so-called North Coast of California, where the climate is more humid than in the central-southern part of the State. In the cold semester, fog often forms at night and in the early morning. From November to March, rainfall is also frequent. On the coldest nights of the year, the temperature generally drops to -3/-5 °C (23/26.5 °F), even though in December 1990, it dropped to -9 °C (16 °F).
In the warm half-year, there are strong temperature variations between night and day, so, even if it can get hot during the day, nights are generally cool (or even a little cold). Even in summer, fog can form at night and in the morning, while the ocean breeze cools the air in the afternoon and evening.
On the hottest days of the year, the temperature can reach 38/40 °C (100/104 °F), and this can also happen in September. It reached 43 °C (109.5 °F) in September 2017 and 44 °C (111 °F) in September 2020. These torrid temperatures occur when the wind blows from the deserts of California.
The average temperature of the coldest month (December) is of 8.4 °C (47.2 °F), that of the warmest month (August) is of 20 °C (68 °F). Here are the average temperatures.

Precipitation amounts to 860 millimeters (33.8 inches) per year: so, it is at an intermediate level. It ranges from 0 mm (0 in) in the driest months (July, August) to 170 mm (6.7 in) in the wettest ones (January, February, December). Here is the average precipitation.

On the coast to the west of Santa Rosa, the sea is cold even in summer, and the air too is much cooler: highs are below 20 °C (68 °F) even in the height of summer. Here is the average sea temperature in Bodega Bay.

Best Time

Santa Rosa can be visited from May to October. In May and October, it is rarely too hot, but sometimes it can rain. From June to September, the temperatures are generally pleasant (warm during the day and cool at night), but sometimes it can get very hot.

Back to California.

Santa Rosa - Weather by month

Based on the period 1991-2020

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In January, the weather in Santa Rosa is usually mild. The average temperature is of 8.7 °C (48 °F), with a minimum of 3.1 °C (37.5 °F) and a maximum of 14.4 °C (57.9 °F).
On the coldest nights of the month, the temperature usually drops to around -2.5 °C (27 °F). However, it dropped to -6.7 °C (19.9 °F) in January 2007.
On the warmest days of the month, the temperature usually reaches around 20.5 °C (68.5 °F). However, it reached 28 °C (82.4 °F) in January 2009.
Precipitation amounts to 170 mm (6.7 in), distributed over 12 days.
The day lasts on average 9 hours and 50 minutes.
The average humidity is 82%. Hence, the air is normally humid.
The average wind speed is 6 kph (4 mph).

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In February, the weather in Santa Rosa is usually mild. The average temperature is of 10.3 °C (51 °F), with a minimum of 4.1 °C (39.4 °F) and a maximum of 16.5 °C (61.7 °F).
On the coldest nights of the month, the temperature usually drops to around -1.5 °C (29.5 °F). However, it dropped to -3.9 °C (25 °F) in February 2018.
On the warmest days of the month, the temperature usually reaches around 23.5 °C (74 °F). However, it reached 29.4 °C (84.9 °F) in February 2016.
Precipitation amounts to 170 mm (6.7 in), distributed over 11 days.
The day lasts on average 10 hours and 50 minutes.
The average humidity is 76%. Hence, the air is normally humid.
The average wind speed is 8 kph (5 mph).

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In March, the weather in Santa Rosa is usually mild. However, there are remarkable differences between night and day. The average temperature is of 11.8 °C (53 °F), with a minimum of 5.2 °C (41.4 °F) and a maximum of 18.4 °C (65.1 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 0.5 °C (32.5 °F). However, it dropped to -2.2 °C (28 °F) in March 2009.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 26 °C (79 °F). However, it reached 31.7 °C (89.1 °F) in March 2004.
Precipitation amounts to 115 mm (4.5 in), distributed over 11 days.
The day lasts on average 12 hours and 0 minutes.
The average humidity is 72%. Hence, the air is normally humid.
The average wind speed is 9 kph (5 mph).

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In April, the weather in Santa Rosa is usually mild. However, there are remarkable differences between night and day. The average temperature is of 13.4 °C (56 °F), with a minimum of 6.2 °C (43.2 °F) and a maximum of 20.6 °C (69 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 1.5 °C (35 °F). However, it dropped to -2 °C (28.4 °F) in April 1998.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 30 °C (85.5 °F). However, it reached 34.4 °C (93.9 °F) in April 2004.
Precipitation amounts to 55 mm (2.2 in), distributed over 8 days.
The day lasts on average 13 hours and 20 minutes.
The average humidity is 67%.
The average wind speed is 10 kph (6 mph).

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In May, the weather in Santa Rosa is usually very mild. However, there are remarkable differences between night and day. The average temperature is of 15.9 °C (61 °F), with a minimum of 8.1 °C (46.6 °F) and a maximum of 23.7 °C (74.7 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 4 °C (39.5 °F). However, it dropped to 1.7 °C (35.1 °F) in May 2010.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 32.5 °C (90.5 °F). However, it reached 38.9 °C (102 °F) in May 2008.
Precipitation amounts to 30 mm (1.2 in), distributed over 4 days.
The day lasts on average 14 hours and 20 minutes. So the days are long.
The average humidity is 64%.
The average wind speed is 10 kph (6 mph).

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In June, the weather in Santa Rosa is usually warm. However, there are remarkable differences between night and day. The average temperature is of 18.9 °C (66 °F), with a minimum of 10.1 °C (50.1 °F) and a maximum of 27.7 °C (81.8 °F).
On the coldest nights, which normally occur at the beginning of the month, the temperature usually drops to around 6.5 °C (43.5 °F). However, it dropped to 3.9 °C (39 °F) in June 1999.
On the warmest days, which normally occur at the end of the month, the temperature usually reaches around 37 °C (98.5 °F). However, it reached 42.2 °C (108 °F) in June 2000.
Precipitation amounts to 10 mm (0.4 in), distributed over 2 days.
The day lasts on average 14 hours and 50 minutes. So the days are long. June 21, the summer solstice, is the longest day of the year in the Northern Hemisphere.
The average humidity is 59%.
The average wind speed is 10 kph (6 mph).

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In July, the weather in Santa Rosa is usually warm. However, there are remarkable differences between night and day. The average temperature is of 19.8 °C (68 °F), with a minimum of 10.9 °C (51.7 °F) and a maximum of 28.6 °C (83.5 °F).
On the coldest nights of the month, the temperature usually drops to around 8 °C (46.5 °F). However, it dropped to 5 °C (41 °F) in July 2009.
On the warmest days of the month, the temperature usually reaches around 37.5 °C (99.5 °F). However, it reached 42.2 °C (108 °F) in July 2006.
Precipitation amounts to only 0 mm (0 in), so on average it never rains in the whole month.
The day lasts on average 14 hours and 30 minutes. So the days are long.
The average humidity is 64%.
The average wind speed is 10 kph (6 mph).

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In August, the warmest month of the year, the weather in Santa Rosa is usually warm. However, there are remarkable differences between night and day. The average temperature is of 20 °C (68 °F), with a minimum of 11.1 °C (51.9 °F) and a maximum of 28.9 °C (84.1 °F).
On the coldest nights of the month, the temperature usually drops to around 7.5 °C (46 °F). However, it dropped to 5.5 °C (41.9 °F) in August 1995.
On the warmest days of the month, the temperature usually reaches around 37.5 °C (99 °F). However, it reached 41.7 °C (107.1 °F) in August 2010.
Precipitation amounts to only 0 mm (0 in), so on average it never rains in the whole month.
The day lasts on average 13 hours and 35 minutes.
The average humidity is 64%.
The average wind speed is 9 kph (5 mph).

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In September, the weather in Santa Rosa is usually warm. However, there are remarkable differences between night and day. The average temperature is of 19.2 °C (67 °F), with a minimum of 9.8 °C (49.6 °F) and a maximum of 28.6 °C (83.4 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around 6 °C (42.5 °F). However, it dropped to 2.8 °C (37 °F) in September 2019.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 37.5 °C (99 °F). However, it reached 43.9 °C (111 °F) in September 2020.
Precipitation amounts to only 5 mm (0.2 in), distributed over 2 days.
The day lasts on average 12 hours and 25 minutes.
The average humidity is 62%.
The average wind speed is 8 kph (5 mph).

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In October, the weather in Santa Rosa is usually very mild. However, there are remarkable differences between night and day. The average temperature is of 16.3 °C (61 °F), with a minimum of 7.5 °C (45.5 °F) and a maximum of 25.1 °C (77.1 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around 2.5 °C (36.5 °F). However, it dropped to -2.8 °C (27 °F) in October 2019.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 34.5 °C (94 °F). However, it reached 39 °C (102.2 °F) in October 1996.
Precipitation amounts to 40 mm (1.6 in), distributed over 4 days.
The day lasts on average 11 hours and 5 minutes.
The average humidity is 63%.
The average wind speed is 7 kph (4 mph).

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In November, the weather in Santa Rosa is usually mild. However, there are remarkable differences between night and day. The average temperature is of 11.5 °C (53 °F), with a minimum of 4.5 °C (40.1 °F) and a maximum of 18.6 °C (65.4 °F).
On the coldest nights, which normally occur at the end of the month, the temperature usually drops to around -1 °C (30.5 °F). However, it dropped to -5 °C (23 °F) in November 2015.
On the warmest days, which normally occur at the beginning of the month, the temperature usually reaches around 26.5 °C (80 °F). However, it reached 31.7 °C (89.1 °F) in November 2008.
Precipitation amounts to 90 mm (3.5 in), distributed over 9 days.
The day lasts on average 10 hours and 5 minutes.
The average humidity is 74%. Hence, the air is normally humid.
The average wind speed is 6 kph (4 mph).

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In December, the coldest month of the year, the weather in Santa Rosa is usually quite mild. The average temperature is of 8.4 °C (47 °F), with a minimum of 2.7 °C (36.9 °F) and a maximum of 14.2 °C (57.5 °F).
On the coldest nights of the month, the temperature usually drops to around -3 °C (27 °F). However, it dropped to -6.1 °C (21 °F) in December 1998.
On the warmest days of the month, the temperature usually reaches around 20 °C (68.5 °F). However, it reached 27.2 °C (81 °F) in December 2013.
Precipitation amounts to 170 mm (6.7 in), distributed over 13 days.
The day lasts on average 9 hours and 30 minutes. December 21, the winter solstice, is the shortest day of the year in the Northern Hemisphere.
The average humidity is 81%. Hence, the air is normally humid.
The average wind speed is 6 kph (4 mph).