Coulee Dam, Washington climate: Normal weather by month, frost dates and records
Coulee Dam's normal year runs from 23°F January nights to 88°F July afternoons, with 11.1 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 9.9°C, January lows of −5°C, July highs of 31°C, 281 mm of precipitation a year.
- NOAA stationCoulee Dam (1 mi SW)
- Station IDUSC00451767
- Location47.95°N 119.00°W
- Elevation1,719 ft (524 m)
- Population1,242
On October 23, the normal high in Coulee Dam is 56°F and the normal low 38°F, and the chance of measurable rain or snow is 27%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Coulee Dam.
- Jan 33° 23°
- Feb 40° 25°
- Mar 51° 32°
- Apr 61° 38°
- May 71° 46°
- Jun 78° 52°
- Jul 88° 59°
- Aug 87° 58°
- Sep 77° 51°
- Oct 60° 40°
- Nov 43° 31°
- Dec 33° 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 Coulee Dam each month?
July is the warmest month, with normal highs of 88°F; January the coldest, with normal lows of 23°F. The most precipitation falls in December (1.42 in), the least in August (0.33 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 33°F | 23°F | 28.0°F | 1.15 | 11 | <1 | 28 | 8 h 50 min |
| February | 40°F | 25°F | 32.4°F | 0.88 | 9 | <1 | 23 | 10 h 10 min |
| March | 51°F | 32°F | 41.1°F | 1.07 | 10 | <1 | 17 | 11 h 50 min |
| April | 61°F | 38°F | 49.2°F | 0.97 | 9 | <1 | 6 | 13 h 40 min |
| May | 71°F | 46°F | 58.3°F | 1.11 | 8 | 1 | <1 | 15 h 10 min |
| June | 78°F | 52°F | 64.9°F | 1.15 | 7 | 3 | <1 | 16 h |
| July | 88°F | 59°F | 73.5°F | 0.49 | 3 | 14 | <1 | 15 h 40 min |
| August | 87°F | 58°F | 72.6°F | 0.33 | 3 | 13 | <1 | 14 h 20 min |
| September | 77°F | 51°F | 63.7°F | 0.36 | 4 | 2 | <1 | 12 h 40 min |
| October | 60°F | 40°F | 50.1°F | 0.94 | 7 | <1 | 3 | 11 h |
| November | 43°F | 31°F | 37.0°F | 1.20 | 11 | <1 | 16 | 9 h 20 min |
| December | 33°F | 24°F | 28.5°F | 1.42 | 12 | <1 | 27 | 8 h 20 min |
| Year (annual) | 60°F | 40°F | 49.9°F | 11.07 | 95 | 33 | 120 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 0°C | −5°C | −2.2°C | 29 mm |
| February | 4°C | −4°C | 0.2°C | 22 mm |
| March | 10°C | 0°C | 5.1°C | 27 mm |
| April | 16°C | 3°C | 9.6°C | 25 mm |
| May | 22°C | 8°C | 14.6°C | 28 mm |
| June | 25°C | 11°C | 18.3°C | 29 mm |
| July | 31°C | 15°C | 23.1°C | 12 mm |
| August | 31°C | 15°C | 22.6°C | 8 mm |
| September | 25°C | 10°C | 17.6°C | 9 mm |
| October | 16°C | 5°C | 10.1°C | 24 mm |
| November | 6°C | −1°C | 2.8°C | 30 mm |
| December | 1°C | −5°C | −1.9°C | 36 mm |
NOAA publishes no 1991-2020 snowfall normal for this station, and no record within 25 miles keeps one, so snow is left out here rather than estimated.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00451767; 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 Coulee Dam?
Normal highs sit between 65°F and 85°F in May, June and September. Of those, September 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 USC00451767.
When is the last frost in Coulee Dam?
In Coulee Dam, the last spring frost (32°F) comes after April 22 in half of years and after May 7 in one year in ten; the first autumn frost comes before October 21 in half of years and before October 6 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 221 year in 10 after May 7; 9 in 10 after April 5
- First autumn frost, half of years before
- October 211 year in 10 before October 6; 9 in 10 before November 5
NOAA puts the median frost-free season at 180 days, and the season without a hard freeze (28°F) at 214 days.
A hard freeze (28°F) comes after April 1 in half of springs and before November 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Coulee Dam in zone 7b in ZIP code 99124, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Coulee Dam's NOAA station is in zone 7a: the coldest night of a typical year reaches 2°F (28 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in Washington · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00451767; 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 Coulee Dam?
In a normal year in Coulee Dam, 33 days a year reach 90°F (3 of them 100°F or more), 120 nights fall to 32°F or colder and 95 days bring measurable precipitation.
- Days at 90°F or more
- 33a normal year
- Days at 100°F or more
- 3a normal year
- Nights at 32°F or colder
- 120a normal year
- Days that stay below freezing
- 34high of 32°F or less
- Days with 0.01 inch of precipitation
- 95a normal year
The highest temperature in this station's record (since 1934) is 113°F, on July 27, 1939; the lowest is −17°F, on January 30, 1950.
The wettest calendar year on that record is 1948, with 20.37 in; the snowiest season is 1955–56, with 50.8 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00451767; records: ACIS (NOAA Regional Climate Centers), station USC00451767. Records use complete months only; a month missing more than three days is left out.
How sunny is Coulee Dam?
Over a year 80% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Coulee Dam, 4.1 kWh per square metre a day. July is the sunniest month (92%) and December the cloudiest (53%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 55% | 1.1 |
| February | 69% | 2.3 |
| March | 71% | 3.5 |
| April | 78% | 5.2 |
| May | 80% | 6.4 |
| June | 81% | 7.0 |
| July | 92% | 7.5 |
| August | 91% | 6.3 |
| September | 86% | 4.6 |
| October | 78% | 2.9 |
| November | 64% | 1.5 |
| December | 53% | 0.9 |
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 Coulee Dam need?
A normal year in Coulee Dam brings 6,151 heating degree days, 14% more than the median U.S. place (5,373), and 689 cooling degree days, 24% 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 2,717 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,147 | 0 |
| February | 913 | 0 |
| March | 741 | 0 |
| April | 476 | 0 |
| May | 227 | 19 |
| June | 84 | 81 |
| July | 10 | 273 |
| August | 11 | 246 |
| September | 108 | 67 |
| October | 462 | 1 |
| November | 841 | 0 |
| December | 1,131 | 0 |
| Year (annual) | 6,151 | 689 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00451767. 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 Coulee Dam been warmer than normal lately?
2025 averaged 52.5°F, 2.6°F above the 1991-2020 normal of 49.9°F. 3 of the 4 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 51.9°F | +2.0°F | 7.83 |
| 2022 | 48.7°F | −1.2°F | 10.81 |
| 2023 | 51.3°F | +1.4°F | 13.65 |
| 2025 | 52.5°F | +2.6°F | 8.02 |
Over 64 complete years from 1940 to 2025, the station's annual mean temperature rose at a fitted 2.3°F per century (+0.13°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00451767; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Coulee Dam's climate compare?
Coulee Dam is warmer than 37 of the other 95 places with their own NOAA record in Washington, and wetter than 17. Across the 7,247 U.S. stations with normals, its annual mean of 49.9°F is warmer than 40%.
In the Köppen classification computed from these normals, Coulee Dam 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 Coulee Dam share this climate record?
6 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.
- Grand Coulee, WA960 people · 1 mi S
- Electric City, WA957 people · 4 mi SW
- Nespelem Community, WA322 people · 15 mi N
- Elmer City, WA255 people · 4 mi NE
- Nespelem, WA200 people · 15 mi N
- Keller, WA195 people · 16 mi NE
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 Coulee Dam's climate
What is the coldest month in Coulee Dam?
January, with a normal high of 33°F and a normal low of 23°F. The warmest is July (88°F by day, 59°F at night).
What is the rainiest month in Coulee Dam?
December, with 1.42 in of precipitation in a normal year; the driest is August with 0.33 in.
What plant hardiness zone is Coulee Dam in?
The USDA's 2023 map puts Coulee Dam in zone 7b in ZIP code 99124, the nearest ZIP area. By the same method at Coulee Dam's NOAA station, the coldest night of a typical year reaches 2°F (28 years, 1991-2020): zone 7a.
How late can frost come in Coulee Dam?
In half of years the last 32°F night comes after April 22; in one year in ten it comes after May 7. Waiting until May 7 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Washington climateThe statewide normals and every place in the state
- Wilbur, WA18 miles from this station, 45.6°F a year
- Hartline, WA19 miles from this station, 48.8°F a year
- Chief Joseph Dam, WA30 miles from this station, 51.0°F a year
- Omak, WA42 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