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San Marcos, California climate

BSh Hot semi-arid

San Marcos has a mildly seasonal warm-temperate climate (Hot semi-arid, Köppen BSh). The hottest month is August with an average daily high near 89°F, while the coldest is December averaging around 44°F at night. Precipitation totals about 15 inches a year and is strongly seasonal — February alone averages 3.6 inches while August barely receives 0.06 inches.

☀️ Summers

Hot

Highs near 89°F in August.

About 45 days a year above 90 °F

❄️ Winters

Cool

Lows near 44°F in December.

About 2 freezing nights a year

🌧️ Rain

Fairly dry

About 15 in of rain a year.

Wettest in February

⛅ Sky & trend

Fairly sunny

More sun than cloud through the year.

+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

San Marcos climate normals (1991–2020)

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°F)	69	69	71	74	77	82	87	89	87	81	75	68
Avg temp (°F)	57	57	60	63	67	71	76	77	75	69	62	56
Avg low (°F)	45	46	49	52	56	60	64	65	63	57	49	44
Precipitation (in)	3.2	3.6	2.2	1.0	0.4	0.1	0.1	0.1	0.2	0.6	1.1	2.1

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Avg high (°F)	69	69	71	74	77	82
Avg temp (°F)	57	57	60	63	67	71
Avg low (°F)	45	46	49	52	56	60
Precipitation (in)	3.2	3.6	2.2	1.0	0.4	0.1

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°F)	87	89	87	81	75	68
Avg temp (°F)	76	77	75	69	62	56
Avg low (°F)	64	65	63	57	49	44
Precipitation (in)	0.1	0.1	0.2	0.6	1.1	2.1

How often — frequency of weather events

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	6	6	5	4	2	0.9	0.7	0.4	0.9	2	3	6
Days with high ≥ 90°F (days)	0.0	0.1	0.5	1	2	4	9	12	10	5	1	—
Days with low ≤ 32°F (days)	0.6	0.2	0.0	0.0	0.1	—	—	—	—	—	0.1	0.5

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Days with measurable rain (days)	6	6	5	4	2	0.9
Days with high ≥ 90°F (days)	0.0	0.1	0.5	1	2	4
Days with low ≤ 32°F (days)	0.6	0.2	0.0	0.0	0.1	—

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	0.7	0.4	0.9	2	3	6
Days with high ≥ 90°F (days)	9	12	10	5	1	—
Days with low ≤ 32°F (days)	—	—	—	—	0.1	0.5

Sky & atmosphere

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	44	46	44	40	43	39	34	27	29	35	34	41
Clear days (≤ 30% cloud)	13	11	12	13	11	11	15	18	17	16	15	14
Partly cloudy days (30–70%)	9	9	12	11	15	15	14	12	10	10	10	9
Cloudy days (≥ 70%)	9	8	8	6	6	4	2	1.0	3	5	5	7
Relative humidity (%)	63	66	66	64	63	55	49	46	49	53	55	61
Wind speed (mph)	5.1	5.5	5.3	5.9	6.0	5.6	5.1	4.7	4.4	4.6	4.9	5.2

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Cloud cover (%)	44	46	44	40	43	39
Clear days (≤ 30% cloud)	13	11	12	13	11	11
Partly cloudy days (30–70%)	9	9	12	11	15	15
Cloudy days (≥ 70%)	9	8	8	6	6	4
Relative humidity (%)	63	66	66	64	63	55
Wind speed (mph)	5.1	5.5	5.3	5.9	6.0	5.6

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	34	27	29	35	34	41
Clear days (≤ 30% cloud)	15	18	17	16	15	14
Partly cloudy days (30–70%)	14	12	10	10	10	9
Cloudy days (≥ 70%)	2	1.0	3	5	5	7
Relative humidity (%)	49	46	49	53	55	61
Wind speed (mph)	5.1	4.7	4.4	4.6	4.9	5.2

Methodology & sources

Temperature & precipitation — the official 1991–2020 climate normals from NOAA's U.S. Climate Normals, measured at Escondido #2 (NOAA GHCN station USC00042863), about 8 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 →