Diablo Dam, Washington climate: Climate normals at a NOAA weather station
Diablo Dam's normal year runs from 30°F January nights to 79°F August afternoons, with 77.4 inches of precipitation and 46 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 9.6°C, January lows of −1°C, August highs of 26°C, 1,966 mm of precipitation a year.
- NOAA stationDiablo Dam
- Station IDUSC00452157
- Location48.71°N 121.14°W
- Elevation891 ft (272 m)
On October 23, the normal high in Diablo Dam is 54°F and the normal low 40°F, and the chance of measurable rain or snow is 57%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Diablo Dam.
- Jan 39° 30°
- Feb 43° 30°
- Mar 49° 33°
- Apr 57° 38°
- May 66° 44°
- Jun 70° 49°
- Jul 78° 53°
- Aug 79° 54°
- Sep 71° 49°
- Oct 58° 42°
- Nov 45° 35°
- Dec 38° 30°
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 Diablo Dam each month?
August is the warmest month, with normal highs of 79°F; January the coldest, with normal lows of 30°F. The most precipitation falls in November (13.66 in), the least in July (1.25 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 39°F | 30°F | 34.0°F | 12.25 | 12.2 | 19 | <1 | 20 | 8 h 40 min |
| February | 43°F | 30°F | 36.7°F | 7.38 | 9.9 | 16 | <1 | 18 | 10 h 10 min |
| March | 49°F | 33°F | 41.1°F | 8.16 | 4.2 | 19 | <1 | 13 | 11 h 50 min |
| April | 57°F | 38°F | 47.4°F | 4.60 | 0.3 | 17 | <1 | 4 | 13 h 40 min |
| May | 66°F | 44°F | 55.2°F | 2.71 | 0.0 | 13 | 1 | <1 | 15 h 10 min |
| June | 70°F | 49°F | 59.8°F | 2.25 | 0.0 | 12 | 2 | <1 | 16 h 10 min |
| July | 78°F | 53°F | 65.8°F | 1.25 | 0.0 | 6 | 4 | <1 | 15 h 50 min |
| August | 79°F | 54°F | 66.4°F | 1.51 | 0.0 | 6 | 5 | <1 | 14 h 30 min |
| September | 71°F | 49°F | 60.1°F | 3.41 | 0.0 | 11 | 1 | <1 | 12 h 40 min |
| October | 58°F | 42°F | 49.5°F | 8.64 | 0.0 | 17 | <1 | 1 | 10 h 50 min |
| November | 45°F | 35°F | 39.8°F | 13.66 | 3.1 | 20 | <1 | 10 | 9 h 10 min |
| December | 38°F | 30°F | 34.2°F | 11.57 | 16.0 | 20 | <1 | 20 | 8 h 20 min |
| Year (annual) | 58°F | 41°F | 49.2°F | 77.39 | 45.7 | 174 | 12 | 86 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 4°C | −1°C | 1.1°C | 311 mm | 31 cm |
| February | 6°C | −1°C | 2.6°C | 187 mm | 25 cm |
| March | 9°C | 1°C | 5.1°C | 207 mm | 11 cm |
| April | 14°C | 3°C | 8.6°C | 117 mm | 1 cm |
| May | 19°C | 7°C | 12.9°C | 69 mm | 0 cm |
| June | 21°C | 10°C | 15.4°C | 57 mm | 0 cm |
| July | 26°C | 12°C | 18.8°C | 32 mm | 0 cm |
| August | 26°C | 12°C | 19.1°C | 38 mm | 0 cm |
| September | 22°C | 9°C | 15.6°C | 87 mm | 0 cm |
| October | 14°C | 5°C | 9.7°C | 219 mm | 0 cm |
| November | 7°C | 2°C | 4.3°C | 347 mm | 8 cm |
| December | 3°C | −1°C | 1.2°C | 294 mm | 41 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00452157; 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 Diablo 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 (6).
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 USC00452157.
When is the last frost at Diablo Dam?
In Diablo Dam, the last spring frost (32°F) comes after April 10 in half of years and after May 1 in one year in ten; the first autumn frost comes before November 1 in half of years and before October 19 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 101 year in 10 after May 1; 9 in 10 after March 22
- First autumn frost, half of years before
- November 11 year in 10 before October 19; 9 in 10 before November 20
NOAA puts the median frost-free season at 203 days, and the season without a hard freeze (28°F) at 247 days.
A hard freeze (28°F) comes after March 13 in half of springs and before November 20 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Diablo Dam in zone 7a in ZIP code 98283, 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 8a: the coldest night of a typical year reaches 11°F (30 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 USC00452157; 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 Diablo Dam?
In a normal year in Diablo Dam, 12 days a year reach 90°F (1 of them 100°F or more), 86 nights fall to 32°F or colder and 174 days bring measurable precipitation.
- Days at 90°F or more
- 12a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 86a normal year
- Days that stay below freezing
- 10high of 32°F or less
- Days with 0.01 inch of precipitation
- 174a normal year
- Days with 1 inch of snow or more
- 13a normal year
The highest temperature in this station's record (since 1914) is 110°F, on June 28, 2021; the lowest is −2°F, on December 30, 1990.
The wettest calendar year on that record is 1990, with 115.34 in; the snowiest season is 2007–08, with 177.3 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00452157; records: ACIS (NOAA Regional Climate Centers), station USC00452157. Records use complete months only; a month missing more than three days is left out.
How sunny is it at Diablo Dam?
Over a year 68% of the sunlight that would reach the ground under clear skies gets through the clouds at Diablo Dam, 3.5 kWh per square metre a day. August is the sunniest month (81%) and December the cloudiest (53%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 55% | 1.1 |
| February | 62% | 2.0 |
| March | 59% | 2.9 |
| April | 63% | 4.3 |
| May | 66% | 5.3 |
| June | 67% | 5.8 |
| July | 81% | 6.7 |
| August | 81% | 5.7 |
| September | 75% | 4.0 |
| October | 64% | 2.3 |
| November | 55% | 1.2 |
| 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 many heating and cooling degree days does Diablo Dam record?
A normal year at Diablo Dam brings 6,005 heating degree days, 12% more than the median U.S. place (5,373), and 245 cooling degree days, 73% fewer than the median (908). Eight months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 1,894 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 961 | 0 |
| February | 791 | 0 |
| March | 743 | 0 |
| April | 530 | 0 |
| May | 314 | 8 |
| June | 182 | 27 |
| July | 65 | 88 |
| August | 55 | 97 |
| September | 171 | 24 |
| October | 481 | 0 |
| November | 758 | 0 |
| December | 956 | 0 |
| Year (annual) | 6,005 | 245 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00452157. 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 Diablo Dam been warmer than normal?
2025 averaged 51.0°F, 1.8°F above the 1991-2020 normal of 49.2°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 49.6°F | +0.4°F | 95.07 | 46.2 |
| 2022 | 48.7°F | −0.5°F | 68.77 | 97.7 |
| 2023 | 50.7°F | +1.5°F | 52.92 | – |
| 2024 | 50.5°F | +1.3°F | 64.67 | 32.6 |
| 2025 | 51.0°F | +1.8°F | 79.26 | 9.8 |
Over 81 complete years from 1916 to 2025, the station's annual mean temperature rose at a fitted 3.1°F per century (+0.17°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00452157; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Diablo Dam's climate compare?
Diablo Dam is warmer than 28 of the 96 places with their own NOAA record in Washington, and wetter than 81. Across the 7,247 U.S. stations with normals, its annual mean of 49.2°F is warmer than 37%.
In the Köppen classification computed from these normals, Diablo 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.
Questions about Diablo Dam's climate
What is the coldest month at Diablo Dam?
January, with a normal high of 39°F and a normal low of 30°F. The warmest is August (79°F by day, 54°F at night).
Does it snow at Diablo Dam?
Yes: 46 inches in a normal year, falling on 16 days with 0.1 inch or more, the most in December (16.0 inches).
What is the rainiest month at Diablo Dam?
November, with 13.66 in of precipitation in a normal year; the driest is July with 1.25 in.
What plant hardiness zone is Diablo Dam in?
The USDA's 2023 map puts Diablo Dam in zone 7a in ZIP code 98283, the nearest ZIP area. By the same method at the station, the coldest night of a typical year reaches 11°F (30 years, 1991-2020): zone 8a.
How late can frost come at Diablo Dam?
In half of years the last 32°F night comes after April 10; in one year in ten it comes after May 1. Waiting until May 1 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Washington climateThe statewide normals and every place in the state
- Ross Dam, WA3 miles from this station, 49.1°F a year
- Newhalem, WA5 miles from this station, 50.2°F a year
- Upper Baker Dam, WA25 miles from this station, 47.4°F a year
- Concrete, WA30 miles from this station, 50.7°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made