Ontario, Oregon climate: Normal weather by month, frost dates and records
Ontario's normal year runs from 24°F January nights to 95°F July afternoons, with 9.5 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 12.1°C, January lows of −4°C, July highs of 35°C, 241 mm of precipitation a year.
- NOAA stationOntario Municipal Airport
- Station IDUSW00024162
- Location44.02°N 117.01°W
- Elevation2,190 ft (668 m)
- Population11,957
On October 22, the normal high in Ontario is 63°F and the normal low 36°F, and the chance of measurable rain or snow is 20%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Ontario.
- Jan 38° 24°
- Feb 47° 28°
- Mar 58° 34°
- Apr 66° 39°
- May 76° 48°
- Jun 85° 55°
- Jul 95° 62°
- Aug 93° 59°
- Sep 83° 49°
- Oct 67° 39°
- Nov 50° 30°
- Dec 39° 24°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Ontario each month?
July is the warmest month, with normal highs of 95°F; January the coldest, with normal lows of 24°F. The most precipitation falls in December (1.39 in), the least in August (0.12 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 38°F | 24°F | 31.3°F | 1.38 | 10 | <1 | 28 | 9 h 10 min |
| February | 47°F | 28°F | 37.5°F | 0.89 | 8 | <1 | 22 | 10 h 30 min |
| March | 58°F | 34°F | 46.1°F | 0.97 | 10 | <1 | 16 | 11 h 50 min |
| April | 66°F | 39°F | 52.7°F | 0.77 | 7 | <1 | 7 | 13 h 20 min |
| May | 76°F | 48°F | 62.1°F | 1.17 | 8 | 2 | 1 | 14 h 40 min |
| June | 85°F | 55°F | 69.8°F | 0.72 | 6 | 8 | <1 | 15 h 30 min |
| July | 95°F | 62°F | 78.3°F | 0.26 | 2 | 25 | <1 | 15 h 10 min |
| August | 93°F | 59°F | 76.2°F | 0.12 | 2 | 21 | <1 | 14 h |
| September | 83°F | 49°F | 66.0°F | 0.29 | 3 | 5 | <1 | 12 h 40 min |
| October | 67°F | 39°F | 52.8°F | 0.64 | 5 | <1 | 8 | 11 h 10 min |
| November | 50°F | 30°F | 39.7°F | 0.88 | 8 | <1 | 20 | 9 h 40 min |
| December | 39°F | 24°F | 31.6°F | 1.39 | 11 | <1 | 26 | 9 h |
| Year (annual) | 67°F | 41°F | 53.7°F | 9.48 | 80 | 61 | 129 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 3°C | −4°C | −0.4°C | 35 mm |
| February | 8°C | −2°C | 3.1°C | 23 mm |
| March | 15°C | 1°C | 7.8°C | 25 mm |
| April | 19°C | 4°C | 11.5°C | 20 mm |
| May | 25°C | 9°C | 16.7°C | 30 mm |
| June | 29°C | 13°C | 21.0°C | 18 mm |
| July | 35°C | 16°C | 25.7°C | 7 mm |
| August | 34°C | 15°C | 24.6°C | 3 mm |
| September | 28°C | 10°C | 18.9°C | 7 mm |
| October | 19°C | 4°C | 11.6°C | 16 mm |
| November | 10°C | −1°C | 4.3°C | 22 mm |
| December | 4°C | −4°C | −0.2°C | 35 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Malheur Branch Experiment Station (3 miles away), gets 15 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00024162; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Ontario?
Normal highs sit between 65°F and 85°F in April, May, June, September and October. Of those, September has the fewest days with rain (3).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00024162.
When is the last frost in Ontario?
In Ontario, the last spring frost (32°F) comes after April 21 in half of years and after May 8 in one year in ten; the first autumn frost comes before October 14 in half of years and before September 29 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 211 year in 10 after May 8; 9 in 10 after April 4
- First autumn frost, half of years before
- October 141 year in 10 before September 29; 9 in 10 before October 29
NOAA puts the median frost-free season at 176 days, and the season without a hard freeze (28°F) at 205 days.
A hard freeze (28°F) comes after April 2 in half of springs and before October 27 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Ontario in zone 7a in ZIP code 83619, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Ontario's NOAA station is in zone 7a: the coldest night of a typical year reaches 2°F (23 complete years).
Frost dates for every NOAA station in Oregon · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00024162; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Ontario?
In a normal year in Ontario, 61 days a year reach 90°F (11 of them 100°F or more), 129 nights fall to 32°F or colder and 80 days bring measurable precipitation.
- Days at 90°F or more
- 61a normal year
- Days at 100°F or more
- 11a normal year
- Nights at 32°F or colder
- 129a normal year
- Days that stay below freezing
- 20high of 32°F or less
- Days with 0.01 inch of precipitation
- 80a normal year
The highest temperature in Ontario's official record (kept by the National Weather Service since 1945) is 113°F, on July 12, 1967; the lowest is −25°F, on January 27, 1957.
The wettest calendar year on that record is 1970, with 14.38 in; the snowiest season is 1983–84, with 41.3 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USW00024162; records: ACIS (NOAA Regional Climate Centers), NWS threaded record ONOthr. Records use complete months only; a month missing more than three days is left out.
How sunny is Ontario?
Over a year 80% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Ontario, 4.4 kWh per square metre a day. July is the sunniest month (92%) and December the cloudiest (58%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 61% | 1.5 |
| February | 68% | 2.5 |
| March | 70% | 3.8 |
| April | 77% | 5.5 |
| May | 79% | 6.5 |
| June | 83% | 7.3 |
| July | 92% | 7.7 |
| August | 91% | 6.6 |
| September | 87% | 5.0 |
| October | 80% | 3.3 |
| November | 68% | 1.9 |
| December | 58% | 1.2 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Ontario need?
A normal year in Ontario brings 5,200 heating degree days, 3% fewer than the median U.S. place (5,373), and 1,100 cooling degree days, 21% more than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,440 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,045 | 0 |
| February | 771 | 0 |
| March | 585 | 0 |
| April | 371 | 2 |
| May | 146 | 57 |
| June | 32 | 176 |
| July | 2 | 414 |
| August | 4 | 349 |
| September | 70 | 98 |
| October | 383 | 4 |
| November | 760 | 0 |
| December | 1,034 | 0 |
| Year (annual) | 5,200 | 1,100 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00024162. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Ontario been warmer than normal lately?
2025 averaged 54.2°F, 0.5°F above the 1991-2020 normal of 53.7°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 55.5°F | +1.8°F | 8.17 |
| 2022 | 52.9°F | −0.8°F | 8.31 |
| 2023 | 54.3°F | +0.6°F | 11.32 |
| 2024 | 55.2°F | +1.5°F | 12.67 |
| 2025 | 54.2°F | +0.5°F | 11.32 |
Over 32 complete years from 1949 to 2025, the station's annual mean temperature rose at a fitted 3.5°F per century (+0.20°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USW00024162; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Ontario's climate compare?
Ontario is warmer than 80 of the other 104 places with their own NOAA record in Oregon, and wetter than 5. Across the 7,247 U.S. stations with normals, its annual mean of 53.7°F is warmer than 56%.
In the Köppen classification computed from these normals, Ontario is BSk: cold semi-arid steppe. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Ontario share this climate record?
2 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Fruitland, ID7,078 people · 5 mi E
- New Plymouth, ID1,608 people · 10 mi E
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Ontario's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near Ontario. This page uses Ontario Municipal Airport; the other differs by site and elevation:
| Station | From this station | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Ontario Ksrv USC00356294 | 3 mi NE | 2,145 ft | 51.6°F | 23°F | 93°F | 10.0 | – | April 22 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Ontario's climate
What is the coldest month in Ontario?
January, with a normal high of 38°F and a normal low of 24°F. The warmest is July (95°F by day, 62°F at night).
Does it snow in Ontario?
Yes. NOAA publishes no 1991-2020 snowfall normal for Ontario's NOAA station; the nearest record that keeps one, Malheur Branch Experiment Station (3 miles away), records 15 inches of snow in a normal year.
What is the rainiest month in Ontario?
December, with 1.39 in of precipitation in a normal year; the driest is August with 0.12 in.
What plant hardiness zone is Ontario in?
The USDA's 2023 map puts Ontario in zone 7a in ZIP code 83619, the nearest ZIP area. By the same method at Ontario's NOAA station, the coldest night of a typical year reaches 2°F (23 years, 1991-2020): zone 7a.
How late can frost come in Ontario?
In half of years the last 32°F night comes after April 21; in one year in ten it comes after May 8. Waiting until May 8 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Oregon climateThe statewide normals and every place in the state
- Malheur Branch Experiment Station, OR3 miles from this station, 52.2°F a year
- Payette, ID6 miles from this station, 53.2°F a year
- Nyssa, OR10 miles from this station, 51.8°F a year
- Vale, OR12 miles from this station, 49.9°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made