Ontario climate

Name: Ontario
Address: US

Ontario is warmest in August, with average highs of 33 °C, and coldest in December, when nights average 6.4 °C. February is the wettest month (101 mm) and August the driest (0.7 mm). Figures are 1991–2020 climate normals.

Across a full year Ontario averages 418 mm of rain, 181 days above 25 °C and 1 days below freezing.

United States · 306 m elevation · population 171,214 · 1991–2020 normals

Temperature below 0 °C to above 30 °C Rain band height is that month’s share of the wettest month

Warmest month August 33 °C
Coldest month December 6.4 °C
Driest month August 1 mm
Wettest month February 101 mm
Least cloud August 13 % cloud
Hottest on record September 46 °C
Coldest on record January -1.9 °C

What to expectOntario through the year

Ontario has a clear annual cycle: average daily highs run from 18 °C in December to 33 °C in August, a swing of 14 °C in mean temperature across the year.

Counted across a normal year, 181 days a year reach 25 °C, 99 of them reach 30 °C, 1 nights drop below freezing. The warmest reading in the 1991–2020 record is 46 °C, in September.

Rain is strongly seasonal. February averages 101 mm against 1 mm in August — 137 times as much. Planning around the dry months matters more here than planning around temperature.

Month by month

Month	Avg high	Rainfall	Cloud
January	18.1 °C	94 mm	47 %
February	18.5 °C	101 mm	49 %
March	20.3 °C	66 mm	48 %
April	22.8 °C	26 mm	40 %
May	25.3 °C	12 mm	35 %
June	28.8 °C	3 mm	21 %
July	32.0 °C	2 mm	18 %
August	33.1 °C	1 mm	13 %
September	31.6 °C	5 mm	17 %
October	27.0 °C	19 mm	26 %
November	22.1 °C	27 mm	35 %
December	17.7 °C	64 mm	43 %

Temperature month by month

Month	Avg high	Avg low	Mean	Record high	Record low	Days above 25 °C	Days above 30 °C
January	18.1 °C	6.7 °C	11.3 °C	30.5 °C	-1.9 °C	2	0
February	18.5 °C	7.1 °C	11.9 °C	30.2 °C	-0.9 °C	3	0
March	20.3 °C	8.5 °C	13.6 °C	32.7 °C	-0.3 °C	5	1
April	22.8 °C	10.1 °C	15.6 °C	35.4 °C	0.2 °C	10	2
May	25.3 °C	12.6 °C	18.2 °C	38.0 °C	5.7 °C	16	5
June	28.8 °C	15.2 °C	21.4 °C	41.4 °C	7.7 °C	25	12
July	32.0 °C	18.4 °C	24.6 °C	45.9 °C	12.0 °C	31	23
August	33.1 °C	19.2 °C	25.4 °C	42.8 °C	13.3 °C	31	26
September	31.6 °C	17.7 °C	23.9 °C	46.2 °C	10.8 °C	28	20
October	27.0 °C	14.0 °C	19.7 °C	40.1 °C	5.5 °C	20	9
November	22.1 °C	9.7 °C	15.0 °C	34.6 °C	0.1 °C	8	2
December	17.7 °C	6.4 °C	11.1 °C	28.4 °C	-1.3 °C	1	0

Rain, sun and wind month by month

Month	Rainfall	Wet days	Daylight	Cloud cover	Humidity	Wind
January	94 mm	6	10 h/day	47 %	63 %	10 km/h
February	101 mm	7	11 h/day	49 %	66 %	11 km/h
March	66 mm	7	12 h/day	48 %	69 %	12 km/h
April	26 mm	4	13 h/day	40 %	64 %	14 km/h
May	12 mm	2	14 h/day	35 %	64 %	14 km/h
June	3 mm	0	14 h/day	21 %	60 %	13 km/h
July	2 mm	0	14 h/day	18 %	57 %	13 km/h
August	1 mm	0	13 h/day	13 %	54 %	13 km/h
September	5 mm	1	12 h/day	17 %	54 %	12 km/h
October	19 mm	3	11 h/day	26 %	54 %	11 km/h
November	27 mm	3	10 h/day	35 %	54 %	10 km/h
December	64 mm	5	9.9 h/day	43 %	60 %	10 km/h

How Ontario compares

The same four figures for nearby destinations, so the numbers above have something to be read against. Summer high is the warmest month's average high; winter low is the coldest month's average low.

Destination	Summer high	Winter low	Rain per year	Days above 25 °C
Ontario	33 °C	6.4 °C	418 mm	181
Pomona · United States	32 °C	6.4 °C	411 mm	176
Fontana · United States	34 °C	4.8 °C	464 mm	180
Corona · United States	33 °C	6.1 °C	438 mm	189
Riverside · United States	34 °C	5.0 °C	439 mm	189
San Bernardino · United States	34 °C	5.0 °C	392 mm	186
Anaheim · United States	29 °C	7.1 °C	317 mm	142

Where Ontario ranks

Ranking	Position	Value
Places with the best weather in North America in April	3rdof 50	96/100
Places with the best weather in North America in November	5thof 50	97/100
The driest places in North America in August	10thof 50	0.7 mm
Places with the best weather in North America in May	14thof 50	94/100
The driest places in North America in July	19thof 50	1.7 mm
The driest places in North America in June	20thof 50	2.6 mm

Planning a trip? See the best time to visit Ontario.

QuestionsCommon questions about Ontario’s climate

When is the best time to visit Ontario?

That depends on what you want, so the honest answer is a comparison rather than a single month. May, June, October sit closest to 20 °C on average, August is the warmest month and August the driest. The month-by-month table above has the full picture.

How hot does Ontario get?

In August, the warmest month, daily highs average 33 °C. About 99 days a year pass 30 °C. The highest value in the 1991–2020 record is 46 °C.

How cold does it get in winter?

Nights average 6.4 °C in December, the coldest month. A normal year has 1 nights below freezing.

Which month is wettest in Ontario?

February, averaging 101 mm over 7 days with rain. The driest month is August with 1 mm. The year as a whole averages 418 mm.

Are these figures a forecast?

No. They are 1991–2020 climate normals: the average of thirty years, which describes what a month is usually like in Ontario rather than what any particular week will bring. Individual years can differ substantially from the normal.

Data sources and method

ERA5 / ERA5-Land reanalysis — Copernicus Climate Change Service (C3S), ECMWF. Copernicus Licence
Open-Meteo — Open-Meteo.com. CC BY 4.0
NOAA OISST v2.1 — NOAA Physical Sciences Laboratory. Public domain
GeoNames — GeoNames.org. CC BY 4.0

Normal period: 1991–2020
Dataset version: era5-1991-2020-scores1.1
Last processed: 1 August 2026

Measured values come from ERA5 reanalysis and are reproduced unchanged. Calculated by us: monthly rankings, daylight hours, beach and comfort scores. Full formulas are on the methodology page.

Contains modified Copernicus Climate Change Service information 2026. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.