Bonneville Dam, Oregon climate: Climate normals at a NOAA weather station
Bonneville Dam's normal year runs from 34°F January nights to 80°F August afternoons, with 80.2 inches of precipitation and 10 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 11.6°C, January lows of 1°C, August highs of 27°C, 2,038 mm of precipitation a year.
- NOAA stationBonneville Dam
- Station IDUSC00350897
- Location45.64°N 121.95°W
- Elevation62 ft (19 m)
On October 23, the normal high in Bonneville Dam is 59°F and the normal low 45°F, and the chance of measurable rain or snow is 55%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Bonneville Dam.
- Jan 43° 34°
- Feb 47° 36°
- Mar 53° 38°
- Apr 59° 42°
- May 67° 48°
- Jun 72° 52°
- Jul 79° 57°
- Aug 80° 58°
- Sep 74° 53°
- Oct 62° 47°
- Nov 50° 40°
- Dec 42° 35°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like at Bonneville Dam each month?
August is the warmest month, with normal highs of 80°F; January the coldest, with normal lows of 34°F. The most precipitation falls in December (13.45 in), the least in July (0.60 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 43°F | 34°F | 38.5°F | 11.31 | 3.5 | 22 | <1 | 10 | 9 h |
| February | 47°F | 36°F | 41.3°F | 8.67 | 3.4 | 18 | <1 | 7 | 10 h 20 min |
| March | 53°F | 38°F | 45.6°F | 9.13 | 0.3 | 20 | <1 | 4 | 11 h 50 min |
| April | 59°F | 42°F | 50.8°F | 6.47 | 0.0 | 19 | <1 | <1 | 13 h 30 min |
| May | 67°F | 48°F | 57.0°F | 4.08 | 0.0 | 15 | <1 | <1 | 14 h 50 min |
| June | 72°F | 52°F | 61.9°F | 3.21 | 0.0 | 11 | 1 | <1 | 15 h 40 min |
| July | 79°F | 57°F | 68.1°F | 0.60 | 0.0 | 4 | 4 | <1 | 15 h 20 min |
| August | 80°F | 58°F | 68.6°F | 0.90 | 0.0 | 4 | 4 | <1 | 14 h 10 min |
| September | 74°F | 53°F | 63.6°F | 2.62 | 0.0 | 8 | 1 | <1 | 12 h 40 min |
| October | 62°F | 47°F | 54.5°F | 7.30 | 0.0 | 15 | <1 | <1 | 11 h |
| November | 50°F | 40°F | 45.0°F | 12.48 | 0.2 | 21 | <1 | 3 | 9 h 30 min |
| December | 42°F | 35°F | 38.5°F | 13.45 | 2.9 | 22 | <1 | 9 | 8 h 40 min |
| Year (annual) | 61°F | 45°F | 52.8°F | 80.22 | 10.3 | 179 | 11 | 33 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 6°C | 1°C | 3.6°C | 287 mm | 9 cm |
| February | 8°C | 2°C | 5.2°C | 220 mm | 9 cm |
| March | 12°C | 3°C | 7.6°C | 232 mm | 1 cm |
| April | 15°C | 6°C | 10.4°C | 164 mm | 0 cm |
| May | 19°C | 9°C | 13.9°C | 104 mm | 0 cm |
| June | 22°C | 11°C | 16.6°C | 82 mm | 0 cm |
| July | 26°C | 14°C | 20.1°C | 15 mm | 0 cm |
| August | 27°C | 14°C | 20.3°C | 23 mm | 0 cm |
| September | 23°C | 12°C | 17.6°C | 67 mm | 0 cm |
| October | 17°C | 8°C | 12.5°C | 185 mm | 0 cm |
| November | 10°C | 4°C | 7.2°C | 317 mm | 1 cm |
| December | 6°C | 2°C | 3.6°C | 342 mm | 7 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00350897; 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.
Which months are mildest at Bonneville Dam?
Normal highs sit between 65°F and 85°F in May, June, July, August and September. Of those, August has the fewest days with rain (4).
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 USC00350897.
When is the last frost at Bonneville Dam?
In Bonneville Dam, the last spring frost (32°F) comes after March 14 in half of years and after April 4 in one year in ten; the first autumn frost comes before November 27 in half of years and before November 8 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
- March 141 year in 10 after April 4; 9 in 10 after February 19
- First autumn frost, half of years before
- November 271 year in 10 before November 8; 9 in 10 before December 15
NOAA puts the median frost-free season at 257 days, and the season without a hard freeze (28°F) at 306 days.
A hard freeze (28°F) comes after February 14 in half of springs and before December 14 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Bonneville Dam in zone 9a in ZIP code 98639, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, the station is in zone 9a: the coldest night of a typical year reaches 20°F (28 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 USC00350897; 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 at Bonneville Dam?
In a normal year in Bonneville Dam, 11 days a year reach 90°F (1 of them 100°F or more), 33 nights fall to 32°F or colder and 179 days bring measurable precipitation.
- Days at 90°F or more
- 11a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 33a normal year
- Days that stay below freezing
- 5high of 32°F or less
- Days with 0.01 inch of precipitation
- 179a normal year
- Days with 1 inch of snow or more
- 3a normal year
The highest temperature in this station's record (since 1937) is 111°F, on June 29, 2021; the lowest is 0°F, on December 31, 1968.
The wettest calendar year on that record is 2012, with 104.96 in; the snowiest season is 1949–50, with 92.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00350897; records: ACIS (NOAA Regional Climate Centers), station USC00350897. Records use complete months only; a month missing more than three days is left out.
How sunny is it at Bonneville Dam?
Over a year 79% of the sunlight that would reach the ground under clear skies gets through the clouds at Bonneville Dam, 4.2 kWh per square metre a day. July is the sunniest month (93%) and December the cloudiest (56%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 57% | 1.3 |
| February | 66% | 2.3 |
| March | 68% | 3.5 |
| April | 75% | 5.1 |
| May | 78% | 6.3 |
| June | 83% | 7.1 |
| July | 93% | 7.7 |
| August | 91% | 6.5 |
| September | 86% | 4.8 |
| October | 76% | 3.0 |
| November | 64% | 1.6 |
| December | 56% | 1.1 |
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 many heating and cooling degree days does Bonneville Dam record?
A normal year at Bonneville Dam brings 4,784 heating degree days, 11% fewer than the median U.S. place (5,373), and 356 cooling degree days, 61% fewer 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 2,407 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 822 | 0 |
| February | 662 | 0 |
| March | 600 | 0 |
| April | 427 | 1 |
| May | 258 | 11 |
| June | 128 | 37 |
| July | 28 | 122 |
| August | 19 | 130 |
| September | 92 | 51 |
| October | 329 | 3 |
| November | 602 | 0 |
| December | 820 | 0 |
| Year (annual) | 4,784 | 356 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00350897. 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.
Have recent years at Bonneville Dam been warmer than normal?
2025 averaged 54.7°F, 1.9°F above the 1991-2020 normal of 52.8°F. 3 of the 4 complete years since 2022 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2022 | 52.6°F | −0.2°F | 78.78 | 45.1 |
| 2023 | 53.6°F | +0.8°F | 68.19 | 2.0 |
| 2024 | 53.2°F | +0.4°F | 83.90 | – |
| 2025 | 54.7°F | +1.9°F | 74.31 | 4.6 |
Over 71 complete years from 1940 to 2025, the station's annual mean temperature rose at a fitted 3.4°F per century (+0.19°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00350897; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Bonneville Dam's climate compare?
Bonneville Dam is warmer than 64 of the 105 places with their own NOAA record in Oregon, and wetter than 91. Across the 7,247 U.S. stations with normals, its annual mean of 52.8°F is warmer than 53%.
In the Köppen classification computed from these normals, Bonneville Dam is Csb: temperate, dry-summer, warm summer. 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 Bonneville Dam share this climate record?
North Bonneville has no NOAA station with 1991-2020 normals of its 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.
- North Bonneville, WA1,418 people · 1 mi NW
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Bonneville Dam's climate
What is the coldest month at Bonneville Dam?
January, with a normal high of 43°F and a normal low of 34°F. The warmest is August (80°F by day, 58°F at night).
Does it snow at Bonneville Dam?
Yes: 10 inches in a normal year, falling on 5 days with 0.1 inch or more, the most in January (3.5 inches).
What is the rainiest month at Bonneville Dam?
December, with 13.45 in of precipitation in a normal year; the driest is July with 0.60 in.
What plant hardiness zone is Bonneville Dam in?
The USDA's 2023 map puts Bonneville Dam in zone 9a in ZIP code 98639, the nearest ZIP area. By the same method at the station, the coldest night of a typical year reaches 20°F (28 years, 1991-2020): zone 9a.
How late can frost come at Bonneville Dam?
In half of years the last 32°F night comes after March 14; in one year in ten it comes after April 4. Waiting until April 4 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Oregon climateThe statewide normals and every place in the state
- Cascade Locks, OR5 miles from this station, 52.6°F a year
- Skamania Fish Hatchery, WA13 miles from this station, 50.9°F a year
- Carson, WA16 miles from this station, 48.3°F a year
- Headworks Portland Water B, OR16 miles from this station, 51.4°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made