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Altadena, California climate

Csa Hot-summer Mediterranean

Altadena has a mildly seasonal warm-temperate climate (Hot-summer Mediterranean, Köppen Csa). The hottest month is August with an average daily high near 91°F, while the coldest is December averaging around 45°F at night. Precipitation totals about 20 inches a year and is strongly seasonal — February alone averages 5.2 inches while August barely receives 0.03 inches.

☀️ Summers

Hot

Highs near 91°F in August.

About 73 days a year above 90 °F

❄️ Winters

Cool

Lows near 45°F in December.

🌧️ Rain

Fairly dry

About 20 in of rain a year.

Wettest in February

⛅ Sky & trend

Sunny

Clear skies most days.

+0.5 °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

Altadena climate normals (1991–2020)

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°F)	68	69	73	76	78	84	89	91	90	83	75	67
Avg temp (°F)	57	58	61	63	66	71	76	77	76	70	62	56
Avg low (°F)	46	46	48	51	54	58	62	63	62	56	50	45
Precipitation (in)	4.5	5.2	3.0	1.1	0.5	0.2	0.1	0.0	0.2	0.8	1.1	3.3

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Avg high (°F)	68	69	73	76	78	84
Avg temp (°F)	57	58	61	63	66	71
Avg low (°F)	46	46	48	51	54	58
Precipitation (in)	4.5	5.2	3.0	1.1	0.5	0.2

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°F)	89	91	90	83	75	67
Avg temp (°F)	76	77	76	70	62	56
Avg low (°F)	62	63	62	56	50	45
Precipitation (in)	0.1	0.0	0.2	0.8	1.1	3.3

How often — frequency of weather events

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	7	8	6	3	3	2	0.6	0.4	0.8	3	3	6
Days with high ≥ 90°F (days)	0.0	0.4	0.9	3	3	6	15	19	16	8	2	—
Days with low ≤ 32°F (days)	0.0	—	—	—	—	—	—	—	—	—	—	0.0

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Days with measurable rain (days)	7	8	6	3	3	2
Days with high ≥ 90°F (days)	0.0	0.4	0.9	3	3	6
Days with low ≤ 32°F (days)	0.0	—	—	—	—	—

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	0.6	0.4	0.8	3	3	6
Days with high ≥ 90°F (days)	15	19	16	8	2	—
Days with low ≤ 32°F (days)	—	—	—	—	—	0.0

Sky & atmosphere

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	47	45	43	36	32	22	18	14	19	27	34	43
Clear days (≤ 30% cloud)	12	11	13	15	17	22	25	27	23	21	17	13
Partly cloudy days (30–70%)	11	9	11	10	10	6	5	3	5	7	9	11
Cloudy days (≥ 70%)	9	8	7	5	4	2	1	0.8	1	4	5	7
Relative humidity (%)	61	65	66	63	63	58	53	49	50	52	52	58
Wind speed (mph)	5.3	5.1	4.8	5.0	4.7	4.3	4.0	3.9	3.9	4.2	4.8	5.4

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Cloud cover (%)	47	45	43	36	32	22
Clear days (≤ 30% cloud)	12	11	13	15	17	22
Partly cloudy days (30–70%)	11	9	11	10	10	6
Cloudy days (≥ 70%)	9	8	7	5	4	2
Relative humidity (%)	61	65	66	63	63	58
Wind speed (mph)	5.3	5.1	4.8	5.0	4.7	4.3

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	18	14	19	27	34	43
Clear days (≤ 30% cloud)	25	27	23	21	17	13
Partly cloudy days (30–70%)	5	3	5	7	9	11
Cloudy days (≥ 70%)	1	0.8	1	4	5	7
Relative humidity (%)	53	49	50	52	52	58
Wind speed (mph)	4.0	3.9	3.9	4.2	4.8	5.4

Methodology & sources

Temperature & precipitation — the official 1991–2020 climate normals from NOAA's U.S. Climate Normals, measured at Pasadena (NOAA GHCN station USC00046719), about 5 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 →