United States · 1991–2020

Best time to visit
Rancho Cucamonga.

April leads for comfortable weather in Rancho Cucamonga: typically 23.8°C by day, 10.6°C at night, with 22 mm of rain. Based on measured 1991–2020 NOAA station history.

Best comfortApril

Typical high23.8°C

Typical low10.6°C

Rain in April22 mm

Comfort

April

April · May · November

91climate match

Beach

June

June · September · July

81climate match

Outdoors

March

March · January · November

91climate match

The weakest month is August, scoring 59 against April’s 91 — days average 34.6°C, 11° above 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

6719.8° / 6.7°

Feb

6519.7° / 7.1°

Mar

8222° / 9°

Apr

9123.8° / 10.6°

May

8926.5° / 13.1°

Jun

7930.1° / 15.4°

Jul

6233.9° / 18.2°

Aug

5934.6° / 18.4°

Sep

6832.6° / 17.2°

Oct

8527.8° / 13.6°

Nov

8723.3° / 9.2°

Dec

6519.1° / 6.2°

Monthly climate evidence for Rancho Cucamonga — daylight is calculated from latitude, everything else is measured
Month	Day	Night	Rain	Wet days	Daylight	Comfort	Coverage
January	19.8°C	6.7°C	56 mm	4.1	10 h 06	67	Good coverage
February	19.7°C	7.1°C	68 mm	5.2	10 h 54	65	Good coverage
March	22°C	9°C	32 mm	3.6	11 h 52	82	Good coverage
April	23.8°C	10.6°C	22 mm	2.5	12 h 59	91	Good coverage
May	26.5°C	13.1°C	8 mm	1.2	13 h 55	89	Good coverage
June	30.1°C	15.4°C	0 mm	0	14 h 25	79	Good coverage
July	33.9°C	18.2°C	1 mm	0.2	14 h 13	62	Good coverage
August	34.6°C	18.4°C	1 mm	0.2	13 h 25	59	Good coverage
September	32.6°C	17.2°C	3 mm	0.3	12 h 21	68	Good coverage
October	27.8°C	13.6°C	12 mm	1.3	11 h 16	85	Good coverage
November	23.3°C	9.2°C	22 mm	2.3	10 h 20	87	Good coverage
December	19.1°C	6.2°C	49 mm	4.3	9 h 53	65	Good coverage

Records at ONTARIO INTL AP, 1998–2026
Month	Record high	Record low	Wettest day	Wettest / driest month	Years
January	32.2°C31 Jan 2003	-3.8°C14 Jan 2007	82 mm9 Jan 2005	207 mm2005 · driest 0 mm in 2003	28
February	32.8°C27 Feb 2026	-1.6°C20 Feb 2018	92 mm5 Feb 2024	287 mm2024 · driest 2 mm in 2020	28
March	37.8°C20 Mar 2026	0.6°C2 Mar 2023	64 mm15 Mar 2003	198 mm2023 · driest 1 mm in 2008	28
April	38.3°C26 Apr 2004	0.6°C10 Apr 1999	42 mm6 Apr 2020	88 mm2020 · driest 0 mm in 2008	28
May	39.4°C3 May 2004	5.6°C1 May 1999	32 mm6 May 2016	32 mm2016 · driest 0 mm in 2022	28
June	44.4°C20 Jun 2016	7.8°C5 Jun 1999	6 mm2 Jun 1999	6 mm1999 · driest 0 mm in 2000	29
July	47.2°C6 Jul 2018	13.3°C9 Jul 2010	11 mm26 Jul 2021	15 mm2015 · driest 0 mm in 2000	29
August	44.4°C31 Aug 2017	13.3°C8 Aug 1999	43 mm20 Aug 2023	49 mm2023 · driest 0 mm in 2022	28
September	47.8°C5 Sep 2020	10.6°C27 Sep 2013	32 mm15 Sep 2015	44 mm2015 · driest 0 mm in 2009	28
October	41.7°C1 Oct 2012	5.0°C31 Oct 2019	35 mm27 Oct 2004	91 mm2004 · driest 0 mm in 2017	28
November	36.7°C3 Nov 2010	0.0°C30 Nov 2004	46 mm28 Nov 2019	102 mm2025 · driest 0 mm in 2017	28
December	30.6°C1 Dec 2021	-2.2°C23 Dec 1998	72 mm21 Dec 2010	199 mm2010 · driest 0 mm in 2024	28

Typical days per month at ONTARIO INTL AP, 1991–2020
Month	Days 25°C+	Days 30°C+	Frost nights	Heavy rain (10 mm+)
January	6	<1	<1	2
February	6	<1	<1	2
March	10	2	0	<1
April	13	5	0	<1
May	19	9	0	<1
June	26	17	0	0
July	31	28	0	0
August	31	29	0	0
September	28	22	0	<1
October	22	12	0	<1
November	12	4	<1	<1
December	4	0	<1	2

How often, not how much — every day in ONTARIO 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	48%	13%	6%	11%	16.7–22.5°C
February	47%	19%	8%	22%	17.0–22.8°C
March	61%	13%	4%	12%	18.5–25.5°C
April	73%	8%	2%	3%	20.8–26.0°C
May	89%	4%	<1%	<1%	24.2–28.4°C
June	98%	<1%	0%	0%	26.7–32.8°C
July	99%	<1%	<1%	0%	32.2–35.8°C
August	99%	<1%	<1%	0%	33.5–36.0°C
September	99%	1%	<1%	0%	30.3–34.5°C
October	91%	4%	1%	<1%	24.6–30.8°C
November	73%	8%	2%	4%	20.5–25.2°C
December	43%	14%	5%	13%	17.2–21.5°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.

1999Each stripe is one year’s mean temperature against the 27-year average. Warmest: 2014. Coolest: 1999.2025

The evidence behind this page

Nearby, measured,
and named.

Place identity: GeoNames 5385955
NOAA station: USW00003102 · ONTARIO INTL AP
Station distance: 6.1 km from the place centre
Climate period: 1991–2020
Minimum month coverage: 22 usable years
Daylight: Calculated from latitude 34.11°, mid-month, sunrise to sunset including refraction. Not a station measurement.
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 ONTARIO INTL AP is what differs

Fontana→Ontario→Upland→Alta Loma→Ballou→Champagne→

Or put two places side by side: Rancho Cucamonga vs Fontana

Best time to visitRancho Cucamonga.