United States · 1991–2020

Best time to visit
South San Francisco.

September leads for comfortable weather in South San Francisco: typically 23.3°C by day, 13.5°C at night, with 2 mm of rain. Based on measured 1991–2020 NOAA station history.

Best comfortSeptember

Typical high23.3°C

Typical low13.5°C

Rain in September2 mm

Comfort

September

September · August · July

95climate match

Beach

September

September · August · July

62climate match

Outdoors

May

May · April · June

97climate match

The weakest month is January, scoring 39 against September’s 95 — days reach only 14°C, 10° below the 24°C the score treats as ideal.

Month by month

The whole year,
without the guesswork.

The bars show the comfort score. Day and night temperatures come from daily observed highs and lows; rain is the historical monthly estimate.

Jan

3914° / 7.2°

Feb

4515.5° / 8.1°

Mar

5617° / 9°

Apr

7018.2° / 9.8°

May

7919.7° / 11.2°

Jun

8721.5° / 12.3°

Jul

9022° / 13.2°

Aug

9322.6° / 13.7°

Sep

9523.3° / 13.5°

Oct

8821.9° / 12.2°

Nov

6417.5° / 9.4°

Dec

3914.1° / 7.3°

Monthly climate evidence for South San Francisco — daylight is calculated from latitude, everything else is measured, sea temperature from the nearest open water 19 km away
Month	Day	Night	Rain	Wet days	Sea	Daylight	Comfort	Coverage
January	14°C	7.2°C	99 mm	8.8	11.9°C	9 h 49	39	Strong coverage
February	15.5°C	8.1°C	100 mm	9.2	12.0°C	10 h 44	45	Strong coverage
March	17°C	9°C	69 mm	8.5	12.1°C	11 h 50	56	Strong coverage
April	18.2°C	9.8°C	35 mm	4.7	11.6°C	13 h 07	70	Strong coverage
May	19.7°C	11.2°C	12 mm	2.3	11.8°C	14 h 11	79	Strong coverage
June	21.5°C	12.3°C	4 mm	0.8	12.4°C	14 h 45	87	Strong coverage
July	22°C	13.2°C	0 mm	0	13.6°C	14 h 31	90	Strong coverage
August	22.6°C	13.7°C	1 mm	0.2	14.4°C	13 h 37	93	Strong coverage
September	23.3°C	13.5°C	2 mm	0.5	14.6°C	12 h 23	95	Strong coverage
October	21.9°C	12.2°C	20 mm	2.1	13.9°C	11 h 09	88	Strong coverage
November	17.5°C	9.4°C	52 mm	5.4	13.1°C	10 h 05	64	Strong coverage
December	14.1°C	7.3°C	105 mm	8.7	12.2°C	9 h 34	39	Strong coverage

What has changed

South San Francisco runs +0.9°C
on the 1961–1990 baseline.

Each bar compares the 2011–2025 daytime average for that month against the same month in 1961–1990, measured at the same station. Months where the older record is too thin to compare are left blank.

Jan

+1.9

Feb

+1.0

Mar

+1.1

Apr

+1.0

May

+0.6

Jun

+0.6

Jul

+0.1

Aug

+0.4

Sep

+0.5

Oct

+1.5

Nov

+1.1

Dec

+1.5

September daytime highs, 2011–2025. Last recorded: 23.6°C.

Records at SAN FRANCISCO INTL AP, 1945–2026
Month	Record high	Record low	Wettest day	Wettest / driest month	Years
January	23.3°C31 Jan 2015	-3.3°C5 Jan 1949	142 mm4 Jan 1982	286 mm1993 · driest 0 mm in 2015	81
February	25.6°C10 Feb 2022	-1.1°C14 Feb 1949	74 mm2 Feb 1998	346 mm1998 · driest 0 mm in 1953	81
March	31.7°C20 Mar 2026	-0.6°C3 Mar 1966	51 mm8 Mar 1978	229 mm1958 · driest 1 mm in 2026	81
April	33.3°C8 Apr 1989	2.2°C27 Apr 1955	58 mm2 Apr 1958	162 mm1958 · driest 0 mm in 1977	81
May	36.1°C27 May 1984	3.9°C3 May 1950	39 mm20 May 1957	97 mm1957 · driest 0 mm in 1984	81
June	40.6°C14 Jun 2000	6.1°C1 Jun 1954	21 mm2 Jun 1967	38 mm2011 · driest 0 mm in 2025	81
July	37.2°C1 Jul 1985	6.7°C29 Jul 1951	9 mm2 Jul 1977	9 mm1977 · driest 0 mm in 1987	82
August	37.2°C24 Aug 2010	7.2°C30 Aug 1955	14 mm19 Aug 1997	17 mm1976 · driest 0 mm in 1956	81
September	40.0°C1 Sep 2017	5.0°C30 Sep 1950	58 mm18 Sep 1959	59 mm1959 · driest 0 mm in 1955	81
October	37.2°C5 Oct 1987	2.8°C20 Oct 1949	102 mm24 Oct 2021	186 mm1962 · driest 0 mm in 2023	81
November	29.4°C2 Nov 1967	-0.6°C30 Nov 1954	65 mm22 Nov 2024	202 mm1973 · driest 0 mm in 1959	81
December	23.9°C2 Dec 1958	-4.4°C9 Dec 1972	93 mm31 Dec 2022	312 mm1955 · driest 0 mm in 1989	81

Typical days per month at SAN FRANCISCO INTL AP, 1991–2020
Month	Days 25°C+	Days 30°C+	Heavy rain (10 mm+)
January	0	0	3
February	0	0	4
March	<1	0	3
April	2	<1	1
May	3	<1	<1
June	5	1	<1
July	4	<1	0
August	5	1	0
September	8	3	0
October	7	2	<1
November	<1	0	2
December	0	0	4

How often, not how much — every day in SAN FRANCISCO INTL AP’s record sorted by what it was actually like, rather than averaged
Month	Warm & dry days	Wet days	Washouts	Week with 3+ wet days	Daytime mean has ranged
January	2%	27%	11%	35%	11.7–15.4°C
February	7%	29%	11%	37%	13.5–17.2°C
March	15%	26%	8%	30%	14.6–18.2°C
April	24%	15%	4%	15%	15.8–20.0°C
May	35%	6%	<1%	4%	17.6–21.4°C
June	59%	2%	<1%	<1%	19.4–23.1°C
July	77%	<1%	0%	0%	20.3–23.5°C
August	82%	<1%	0%	<1%	20.7–23.8°C
September	80%	2%	<1%	<1%	21.3–25.1°C
October	60%	7%	3%	7%	19.7–23.5°C
November	19%	19%	6%	23%	15.5–19.0°C
December	2%	27%	11%	33%	11.9–15.3°C

A warm and dry day reaches 20°C with under 1 mm of rain; a wet day gets 1 mm or more; a washout gets 10 mm or more. The week column is the share of seven-day stretches in that month, across the station’s whole daily record, that contained three or more wet days — the odds a week-long trip is rained on repeatedly, counted rather than modelled. The last column is the 10th to 90th percentile of that month’s daytime average across individual years: a narrow band means the average is what you will get, a wide one means the average is a midpoint between years that felt quite different.

1946Each stripe is one year’s mean temperature against the 80-year average. Warmest: 2014. Coolest: 1949.2025

The evidence behind this page

Nearby, measured,
and named.

Place identity: GeoNames 5397765
NOAA station: USW00023234 · SAN FRANCISCO INTL AP
Station distance: 5.4 km from the place centre
Climate period: 1991–2020
Minimum month coverage: 30 usable years
Daylight: Calculated from latitude 37.65°, mid-month, sunrise to sunset including refraction. Not a station measurement.
Sea temperature: NOAA OISST v2.1 1991–2020 monthly climatology, nearest open water 19 km from the place centre. A sheltered bay can run warmer than the open sea it is measured from.
Important limit: Historical climate is not a forecast. Nearby stations can miss mountains, coasts, and local microclimates.

These places read the same station, so their numbers are identical — distance from SAN FRANCISCO INTL AP is what differs

San Mateo→San Bruno→Burlingame→Millbrae→Hillsborough→Brisbane→

Or put two places side by side: South San Francisco vs San Mateo

Best time to visitSouth San Francisco.

September

September

May

The whole year,without the guesswork.

South San Francisco runs +0.9°Con the 1961–1990 baseline.

Nearby, measured,and named.

Best time to visit
South San Francisco.

The whole year,
without the guesswork.

South San Francisco runs +0.9°C
on the 1961–1990 baseline.

Nearby, measured,
and named.