Ontario, CA climate
Ontario has warm winters and hot summers, with very little rain. A typical July afternoon reaches 92°, a January night drops to 43°, and snow is almost unheard of.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Ontario feels like
Winter
Spring
Summer
Fall
Ontario weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 69° | 43° | 2.9" | 0 | 5 | 0 | 52° – 61° |
| February | 69° | 44° | 3.3" | 0 | 6 | 0 | 49° – 67° |
| March | 72° | 46° | 1.9" | 0 | 4 | 0 | 53° – 66° |
| April | 76° | 49° | 0.8" | 0 | 2 | 0 | 57° – 66° |
| May | 79° | 54° | 0.3" | 0 | 1 | 0 | 61° – 72° |
| June | 86° | 58° | 0.0" | 0 | 0 | 0 | 67° – 77° |
| July | 92° | 62° | 0.0" | 0 | 0 | 0 | 74° – 84° |
| August | 94° | 63° | 0.0" | 0 | 0 | 0 | 75° – 82° |
| September | 91° | 60° | 0.1" | 0 | 0 | 0 | 71° – 80° |
| October | 83° | 55° | 0.5" | 0 | 3 | 0 | 64° – 74° |
| November | 75° | 47° | 0.9" | 0 | 3 | 0 | 54° – 66° |
| December | 68° | 42° | 2.0" | 0 | 5 | 0 | 51° – 61° |
| Year | 79° | 52° | 12.6" | 0.0" | 31 | 0 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in Ontario
Ontario gets 13 inches of rain and melted snow a year. February is the wettest month and July the driest. Rain or snow falls on about 31 days a year.
A year-round growing season
Heating and cooling a home in Ontario
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Ontario, 40% of that work is heating and 60% is cooling, so air conditioning is the bigger bill.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
Ontario and its neighbors
Ontario borders 5 towns with climate data. January nights across them vary by 1.0°. Eastvale has the coldest January nights (43°) and Fontana the hottest July afternoons (94°). Ontario’s January low is 43° and its July high 92°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How Ontario compares
Compared with every U.S. town and city on TownTapestry, each counted once.
Warmer than it used to be
The last 30 years in Ontario averaged 2.6° warmer than the 1900s. The biggest change is in January (+3.4°). The shift is larger than in 100% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Ontario’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. February swings the most: between 1991 and 2020 its average temperature ranged from 49° to 67°. August is the most reliable, staying within 7°.
Common questions about Ontario’s climate
What is the coldest month in Ontario?
December, with a typical high of 68° and a low of 42°.
What is the hottest month in Ontario?
August, with a typical high of 94° and a low of 63°. About 93 days a year reach 90°.
How much snow does Ontario get?
Almost none. A normal year brings 0.0 inches.
When is the first frost in Ontario?
Frost is uncommon. Only 41% of years see a night at 32° or below.
What is the rainiest month in Ontario?
February, with 3.3 inches of rain and melted snow. The year totals 13 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Ontario itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Pomona/fairplex, CA (10 mi, snow) and Ontario Intl Airport, CA (1 mi, frost, heat and degree days). Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.