Climateby Month

Ontario, CA climate by month

NOAA 1991-2020 normals · 1,001 ft elevation · also covers Rancho Cucamonga

Ontario has hot summers and mild winters. Highs peak at 95°F in August and fall to 67°F in December. The wettest month is February (about 6 wet days) and the driest is June (about 0). Snow is rare. By our comfort score the best months are March, April and May.

Warmest month
95°F
August normal high
Coldest month
44°F
December normal low
Wet days a year
35
11.6 in of precipitation
Muggy days a year
2
dew point 65°F or higher

How warm is Ontario?

Normal highs range from 67°F in December to 95°F in August.

40°60°80°100° January: normal high 68°F (20°C), low 45°F (7°C) February: normal high 68°F (20°C), low 46°F (8°C) March: normal high 72°F (22°C), low 49°F (9°C) April: normal high 76°F (24°C), low 51°F (11°C) May: normal high 80°F (27°C), low 56°F (13°C) June: normal high 86°F (30°C), low 60°F (16°C) July: normal high 94°F (34°C), low 65°F (18°C) August: normal high 95°F (35°C), low 65°F (18°C) 95° 65° September: normal high 91°F (33°C), low 64°F (18°C) October: normal high 83°F (28°C), low 57°F (14°C) November: normal high 75°F (24°C), low 49°F (9°C) December: normal high 67°F (19°C), low 44°F (7°C) 67° 44° JFMAMJJASOND

Bars run from the normal low to the normal high for each month.

How rainy is Ontario?

February has the most wet days (about 6); the year brings about 12 in of precipitation.

January: 5 wet days February: 6 wet days 6 March: 5 wet days April: 4 wet days May: 2 wet days June: 0 wet days 0 July: 1 wet days August: 0 wet days September: 1 wet days October: 2 wet days November: 4 wet days December: 6 wet days JFMAMJJASOND

Wet day: at least 0.01 in of rain or melted snow, counted from daily records 1991-2020.

How humid is Ontario?

Muggy days peak in July, at about 1 days.

January: 0 muggy days 0 February: 0 muggy days March: 0 muggy days April: 0 muggy days May: 0 muggy days June: 0 muggy days July: 1 muggy days 1 August: 0 muggy days September: 1 muggy days October: 0 muggy days November: 0 muggy days December: 0 muggy days JFMAMJJASOND

Muggy day: daily mean dew point of 65°F or higher, from hourly observations 1991-2020 at March Air Reserve Base, 26 mi ESE of the city center (the nearest airport with complete hourly records).

How much daylight?

Daylight ranges from about 9.9 hours in December to 14.4 hours in June.

January: 10.2 hours of daylight February: 11.0 hours of daylight March: 12.0 hours of daylight April: 13.1 hours of daylight May: 13.9 hours of daylight June: 14.4 hours of daylight 14.4 July: 14.2 hours of daylight August: 13.4 hours of daylight September: 12.4 hours of daylight October: 11.3 hours of daylight November: 10.4 hours of daylight December: 9.9 hours of daylight 9.9 JFMAMJJASOND
See all numbers
Monthly climate normals and day counts for Ontario, 1991-2020
MonthHighLowPrecip.Wet daysMuggy daysDaylight
January 68°F45°F 2.6 in5 0 10.2 h
February 68°F46°F 3.1 in6 0 11.0 h
March 72°F49°F 1.6 in5 0 12.0 h
April 76°F51°F 0.8 in4 0 13.1 h
May 80°F56°F 0.3 in2 0 13.9 h
June 86°F60°F 0.02 in0 0 14.4 h
July 94°F65°F 0.05 in1 1 14.2 h
August 95°F65°F 0.03 in0 0 13.4 h
September 91°F64°F 0.1 in1 1 12.4 h
October 83°F57°F 0.4 in2 0 11.3 h
November 75°F49°F 0.8 in4 0 10.4 h
December 67°F44°F 1.9 in6 0 9.9 h

High and low: NOAA 1991-2020 normal daily high and low. Wet days: at least 0.01 in of rain or melted snow. Muggy days: daily mean dew point 65°F or higher.

Best months to visit Ontario

By our comfort score, the best months are March, April and May.

Comfort score by month (0-100) and its parts, in days per month
MonthScoreComfortableNotable rainHot or cold
Jan 661630
Feb 641350
Mar 711731
Apr 731623
May 741615
Jun 617011
Jul 441023
Aug 410024
Sep 474018
Oct 601218
Nov 701822
Dec 641530

Score = 40 × share of comfortable days + 25 × share of days without notable rain + 20 × share of days neither hot (90°F+) nor cold (high 40°F or below) + 15 × daylight. How the score works.

Frost dates in Ontario

A night at 32°F or below happens in about 41% of years in Ontario, so there is no typical frost date. In most years there is no frost at all.

Station: Ontario Intl Airport (USW00003102), NOAA 1991-2020 freeze probabilities. Frost dates for every city in California.

Hottest and coldest readings, 1991-2020

The highest reading was 118°F (September 5, 2020); the lowest was 25°F (January 14, 2007).

From the temperature station's daily records with NOAA quality flags removed. Not an all-time record.

Near Ontario

Similar climates elsewhere

Also covers

Rancho Cucamonga uses the same temperature and rain stations as Ontario, so its monthly numbers are the ones on this page.

Where the numbers come from

  • Temperature, rain and frost dates: Ontario Intl Airport (USW00003102), 2.9 mi E of the city center, 949 ft (52 ft lower than the city). NOAA normals and daily records, 1991-2020.
  • Snowfall and snow depth: San Gabriel Canyon PH (USC00047776), 16 mi WNW of the city center, 744 ft (257 ft lower than the city). NOAA normals and daily records, 1991-2020.
  • Humidity and wind by hour and cloud cover: March AFB (USW00023119), 26 mi ESE of the city center, 1,516 ft (515 ft higher than the city). NOAA normals and daily records, 1991-2020.
  • Daily humidity and wind: March Air Reserve Base (722860-23119), 26 mi ESE of the city center, 1,536 ft (535 ft higher than the city). Hourly observations, 1991-2020.

Distances from the city center (USGS). Methodology · Report an error