Ross Dam, Washington climate: Climate normals at a NOAA weather station
Ross Dam's normal year runs from 30°F January nights to 79°F August afternoons, with 60.8 inches of precipitation and 67 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 9.5°C, January lows of −1°C, August highs of 26°C, 1,543 mm of precipitation a year.
- NOAA stationRoss Dam
- Station IDUSC00457185
- Location48.73°N 121.07°W
- Elevation1,236 ft (377 m)
On October 23, the normal high in Ross Dam is 52°F and the normal low 41°F, and the chance of measurable rain or snow is 58%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Ross Dam.
- Jan 38° 30°
- Feb 41° 31°
- Mar 47° 33°
- Apr 56° 38°
- May 65° 45°
- Jun 70° 50°
- Jul 79° 55°
- Aug 79° 56°
- Sep 70° 50°
- Oct 56° 43°
- Nov 44° 35°
- Dec 38° 31°
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 Ross 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 (11.07 in), the least in July (0.99 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 38°F | 30°F | 33.8°F | 9.72 | 17.2 | 19 | <1 | 18 | 8 h 40 min |
| February | 41°F | 31°F | 35.9°F | 5.98 | 11.9 | 15 | <1 | 17 | 10 h 10 min |
| March | 47°F | 33°F | 40.2°F | 6.37 | 7.8 | 18 | <1 | 13 | 11 h 50 min |
| April | 56°F | 38°F | 46.8°F | 3.23 | 0.3 | 15 | <1 | 3 | 13 h 40 min |
| May | 65°F | 45°F | 54.9°F | 2.06 | 0.0 | 12 | <1 | <1 | 15 h 10 min |
| June | 70°F | 50°F | 59.9°F | 1.68 | 0.0 | 11 | 1 | <1 | 16 h 10 min |
| July | 79°F | 55°F | 66.8°F | 0.99 | 0.0 | 6 | 4 | <1 | 15 h 50 min |
| August | 79°F | 56°F | 67.4°F | 1.21 | 0.0 | 6 | 4 | <1 | 14 h 30 min |
| September | 70°F | 50°F | 60.4°F | 2.50 | 0.0 | 11 | 1 | <1 | 12 h 40 min |
| October | 56°F | 43°F | 49.2°F | 6.72 | 0.0 | 16 | <1 | 1 | 10 h 50 min |
| November | 44°F | 35°F | 39.5°F | 11.07 | 5.8 | 20 | <1 | 8 | 9 h 10 min |
| December | 38°F | 31°F | 34.0°F | 9.23 | 23.7 | 19 | <1 | 19 | 8 h 20 min |
| Year (annual) | 57°F | 41°F | 49.1°F | 60.76 | 66.7 | 168 | 10 | 78 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 3°C | −1°C | 1.0°C | 247 mm | 44 cm |
| February | 5°C | −1°C | 2.2°C | 152 mm | 30 cm |
| March | 8°C | 1°C | 4.6°C | 162 mm | 20 cm |
| April | 13°C | 3°C | 8.2°C | 82 mm | 1 cm |
| May | 18°C | 7°C | 12.7°C | 52 mm | 0 cm |
| June | 21°C | 10°C | 15.5°C | 43 mm | 0 cm |
| July | 26°C | 13°C | 19.3°C | 25 mm | 0 cm |
| August | 26°C | 13°C | 19.7°C | 31 mm | 0 cm |
| September | 21°C | 10°C | 15.8°C | 64 mm | 0 cm |
| October | 13°C | 6°C | 9.6°C | 171 mm | 0 cm |
| November | 7°C | 2°C | 4.2°C | 281 mm | 15 cm |
| December | 3°C | −1°C | 1.1°C | 234 mm | 60 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00457185; 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 Ross 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 USC00457185.
When is the last frost at Ross Dam?
In Ross Dam, the last spring frost (32°F) comes after April 8 in half of years and after April 30 in one year in ten; the first autumn frost comes before November 10 in half of years and before October 26 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 81 year in 10 after April 30; 9 in 10 after March 16
- First autumn frost, half of years before
- November 101 year in 10 before October 26; 9 in 10 before November 25
NOAA puts the median frost-free season at 214 days, and the season without a hard freeze (28°F) at 257 days.
A hard freeze (28°F) comes after March 11 in half of springs and before November 25 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Ross 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 (29 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 USC00457185; 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 Ross Dam?
In a normal year in Ross Dam, 10 days a year reach 90°F, 78 nights fall to 32°F or colder and 168 days bring measurable precipitation.
- Days at 90°F or more
- 10a normal year
- Days at 100°F or more
- fewer than 1a normal year
- Nights at 32°F or colder
- 78a normal year
- Days that stay below freezing
- 12high of 32°F or less
- Days with 0.01 inch of precipitation
- 168a normal year
- Days with 1 inch of snow or more
- 18a normal year
The highest temperature in this station's record (since 1960) is 108°F, on June 29, 2021; the lowest is −1°F, on January 1, 1979.
The wettest calendar year on that record is 2014, with 80.61 in; the snowiest season is 2007–08, with 148.4 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00457185; records: ACIS (NOAA Regional Climate Centers), station USC00457185. Records use complete months only; a month missing more than three days is left out.
How sunny is it at Ross Dam?
Over a year 68% of the sunlight that would reach the ground under clear skies gets through the clouds at Ross 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 Ross Dam record?
A normal year at Ross Dam brings 6,083 heating degree days, 13% more than the median U.S. place (5,373), and 303 cooling degree days, 67% 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 1,954 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 969 | 0 |
| February | 815 | 0 |
| March | 767 | 0 |
| April | 546 | 0 |
| May | 318 | 7 |
| June | 182 | 29 |
| July | 58 | 115 |
| August | 47 | 122 |
| September | 168 | 30 |
| October | 489 | 0 |
| November | 765 | 0 |
| December | 959 | 0 |
| Year (annual) | 6,083 | 303 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00457185. 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 Ross Dam been warmer than normal?
2025 averaged 50.6°F, 1.5°F above the 1991-2020 normal of 49.1°F. 4 of the 4 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 49.2°F | +0.1°F | 74.25 | – |
| 2023 | 49.9°F | +0.8°F | 41.48 | – |
| 2024 | 49.8°F | +0.7°F | 50.16 | – |
| 2025 | 50.6°F | +1.5°F | 67.27 | – |
Over 48 complete years from 1961 to 2025, the station's annual mean temperature rose at a fitted 3.2°F per century (+0.18°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00457185; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Ross Dam's climate compare?
Ross Dam is warmer than 27 of the 96 places with their own NOAA record in Washington, and wetter than 74. Across the 7,247 U.S. stations with normals, its annual mean of 49.1°F is warmer than 36%.
In the Köppen classification computed from these normals, Ross 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 Ross Dam's climate
What is the coldest month at Ross Dam?
January, with a normal high of 38°F and a normal low of 30°F. The warmest is August (79°F by day, 56°F at night).
Does it snow at Ross Dam?
Yes: 67 inches in a normal year, falling on 20 days with 0.1 inch or more, the most in December (23.7 inches).
What is the rainiest month at Ross Dam?
November, with 11.07 in of precipitation in a normal year; the driest is July with 0.99 in.
What plant hardiness zone is Ross Dam in?
The USDA's 2023 map puts Ross 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 (29 years, 1991-2020): zone 8a.
How late can frost come at Ross Dam?
In half of years the last 32°F night comes after April 8; in one year in ten it comes after April 30. Waiting until April 30 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Washington climateThe statewide normals and every place in the state
- Diablo Dam, WA3 miles from this station, 49.2°F a year
- Newhalem, WA9 miles from this station, 50.2°F a year
- Upper Baker Dam, WA29 miles from this station, 47.4°F a year
- Stehekin (4 mi NW), WA30 miles from this station, 47.8°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made