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Napa, California climate

Csb Warm-summer Mediterranean

Napa has a mildly seasonal mild-temperate climate (Warm-summer Mediterranean, Köppen Csb). The hottest month is September with an average daily high near 76°F, while the coldest is December averaging around 43°F at night. Precipitation totals about 26 inches a year and is strongly seasonal — December alone averages 5.3 inches while July barely receives 0.01 inches.

☀️ Summers

Mild

Highs near 76°F in September.

About 6 days a year above 90 °F

❄️ Winters

Cool

Lows near 43°F in December.

🌧️ Rain

Moderate rainfall

About 26 in of rain a year.

Wettest in December

⛅ Sky & trend

Partly cloudy

A roughly even mix of sun and cloud.

+0.9 °F vs 50 years ago

Temperature & precipitation

Daily high–low temperature range with the monthly average, plus monthly precipitation · 1991–2020 normals · hover a month for the exact figures

Clear vs cloudy days

Share of days each month that are clear, partly cloudy or cloudy · 1991–2020 · hover a month for the day counts

Napa climate normals (1991–2020)

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°F)	59	62	65	67	70	74	74	75	76	73	65	59
Avg temp (°F)	51	53	55	57	60	63	64	64	65	63	56	51
Avg low (°F)	43	45	46	47	49	52	53	54	54	52	47	43
Precipitation (in)	4.8	5.1	3.8	1.8	0.8	0.3	0.0	0.1	0.1	1.2	2.7	5.3

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Avg high (°F)	59	62	65	67	70	74
Avg temp (°F)	51	53	55	57	60	63
Avg low (°F)	43	45	46	47	49	52
Precipitation (in)	4.8	5.1	3.8	1.8	0.8	0.3

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°F)	74	75	76	73	65	59
Avg temp (°F)	64	64	65	63	56	51
Avg low (°F)	53	54	54	52	47	43
Precipitation (in)	0.0	0.1	0.1	1.2	2.7	5.3

How often — frequency of weather events

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	10	10	9	7	3	1	0.3	0.5	1.0	3	7	10
Days with high ≥ 90°F (days)	—	—	—	0.2	0.6	1	0.4	0.7	2	0.8	—	—
Days with low ≤ 32°F (days)	0.4	0.0	—	—	—	—	—	—	—	—	—	0.3

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Days with measurable rain (days)	10	10	9	7	3	1
Days with high ≥ 90°F (days)	—	—	—	0.2	0.6	1
Days with low ≤ 32°F (days)	0.4	0.0	—	—	—	—

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	0.3	0.5	1.0	3	7	10
Days with high ≥ 90°F (days)	0.4	0.7	2	0.8	—	—
Days with low ≤ 32°F (days)	—	—	—	—	—	0.3

Sky & atmosphere

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	60	61	60	55	54	48	58	59	51	47	51	57
Clear days (≤ 30% cloud)	7	6	7	8	8	10	4	4	9	11	10	8
Partly cloudy days (30–70%)	9	8	11	11	11	11	15	14	11	11	10	9
Cloudy days (≥ 70%)	15	14	14	11	12	9	12	13	10	9	10	14
Relative humidity (%)	84	83	82	80	78	74	74	73	70	69	76	82
Wind speed (mph)	4.8	5.1	5.1	5.4	5.4	5.5	5.1	5.0	4.5	4.3	4.4	5.1

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Cloud cover (%)	60	61	60	55	54	48
Clear days (≤ 30% cloud)	7	6	7	8	8	10
Partly cloudy days (30–70%)	9	8	11	11	11	11
Cloudy days (≥ 70%)	15	14	14	11	12	9
Relative humidity (%)	84	83	82	80	78	74
Wind speed (mph)	4.8	5.1	5.1	5.4	5.4	5.5

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	58	59	51	47	51	57
Clear days (≤ 30% cloud)	4	4	9	11	10	8
Partly cloudy days (30–70%)	15	14	11	11	10	9
Cloudy days (≥ 70%)	12	13	10	9	10	14
Relative humidity (%)	74	73	70	69	76	82
Wind speed (mph)	5.1	5.0	4.5	4.3	4.4	5.1

Methodology & sources

Temperature & precipitation — the official 1991–2020 climate normals from NOAA's U.S. Climate Normals, measured at Berkeley (NOAA GHCN station USC00040693), about 47 km from the city centre.

Cloud, humidity, wind & sunshine — modelled estimates from NASA POWER, NASA's satellite-and-reanalysis climatology. This is the standard global source for atmospheric variables, which are not measured at most weather stations.

How we build these numbers →