Boundary Dam, Washington climate: Climate normals at a NOAA weather station
Boundary Dam's normal year runs from 21°F January nights to 84°F July afternoons, with 28.2 inches of precipitation and 55 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 7.8°C, January lows of −6°C, July highs of 29°C, 716 mm of precipitation a year.
- NOAA stationBoundary Dam
- Station IDUSC00450844
- Location48.99°N 117.35°W
- Elevation1,837 ft (560 m)
On October 23, the normal high in Boundary Dam is 51°F and the normal low 33°F, and the chance of measurable rain or snow is 43%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Boundary Dam.
- Jan 33° 21°
- Feb 38° 22°
- Mar 48° 27°
- Apr 58° 33°
- May 67° 41°
- Jun 72° 48°
- Jul 84° 52°
- Aug 85° 50°
- Sep 73° 43°
- Oct 56° 35°
- Nov 40° 28°
- Dec 32° 21°
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 Boundary Dam each month?
July is the warmest month, with normal highs of 84°F; January the coldest, with normal lows of 21°F. The most precipitation falls in December (3.60 in), the least in August (0.81 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 33°F | 21°F | 26.7°F | 3.10 | 18.5 | 15 | <1 | 31 | 8 h 40 min |
| February | 38°F | 22°F | 29.9°F | 1.98 | 7.7 | 11 | <1 | 27 | 10 h 10 min |
| March | 48°F | 27°F | 37.1°F | 2.35 | 3.4 | 12 | <1 | 28 | 11 h 50 min |
| April | 58°F | 33°F | 45.3°F | 2.21 | 0.1 | 13 | <1 | 16 | 13 h 40 min |
| May | 67°F | 41°F | 54.0°F | 2.60 | 0.0 | 13 | <1 | 3 | 15 h 10 min |
| June | 72°F | 48°F | 60.1°F | 3.18 | 0.0 | 14 | 2 | <1 | 16 h 10 min |
| July | 84°F | 52°F | 67.8°F | 1.42 | 0.0 | 7 | 9 | <1 | 15 h 50 min |
| August | 85°F | 50°F | 67.2°F | 0.81 | 0.0 | 5 | 10 | <1 | 14 h 30 min |
| September | 73°F | 43°F | 57.8°F | 1.32 | 0.0 | 8 | 1 | 2 | 12 h 40 min |
| October | 56°F | 35°F | 45.2°F | 2.40 | 0.1 | 12 | <1 | 13 | 10 h 50 min |
| November | 40°F | 28°F | 34.2°F | 3.23 | 6.8 | 15 | <1 | 23 | 9 h 10 min |
| December | 32°F | 21°F | 26.8°F | 3.60 | 18.2 | 16 | <1 | 30 | 8 h 20 min |
| Year (annual) | 57°F | 35°F | 46.0°F | 28.20 | 54.8 | 141 | 22 | 174 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 0°C | −6°C | −2.9°C | 79 mm | 47 cm |
| February | 3°C | −6°C | −1.2°C | 50 mm | 20 cm |
| March | 9°C | −3°C | 2.8°C | 60 mm | 9 cm |
| April | 14°C | 0°C | 7.4°C | 56 mm | 0 cm |
| May | 20°C | 5°C | 12.2°C | 66 mm | 0 cm |
| June | 22°C | 9°C | 15.6°C | 81 mm | 0 cm |
| July | 29°C | 11°C | 19.9°C | 36 mm | 0 cm |
| August | 29°C | 10°C | 19.6°C | 21 mm | 0 cm |
| September | 23°C | 6°C | 14.3°C | 34 mm | 0 cm |
| October | 13°C | 1°C | 7.3°C | 61 mm | 0 cm |
| November | 5°C | −2°C | 1.2°C | 82 mm | 17 cm |
| December | 0°C | −6°C | −2.9°C | 91 mm | 46 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00450844; 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 Boundary 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 (5).
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 USC00450844.
When is the last frost at Boundary Dam?
In Boundary Dam, the last spring frost (32°F) comes after May 4 in half of years and after May 18 in one year in ten; the first autumn frost comes before October 4 in half of years and before September 21 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
- May 41 year in 10 after May 18; 9 in 10 after April 20
- First autumn frost, half of years before
- October 41 year in 10 before September 21; 9 in 10 before October 20
NOAA puts the median frost-free season at 153 days, and the season without a hard freeze (28°F) at 184 days.
A hard freeze (28°F) comes after April 17 in half of springs and before October 19 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Boundary Dam in zone 6a in ZIP code 99152, 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 6b: the coldest night of a typical year reaches −4°F (26 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 USC00450844; 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 Boundary Dam?
In a normal year in Boundary Dam, 22 days a year reach 90°F (1 of them 100°F or more), 174 nights fall to 32°F or colder and 141 days bring measurable precipitation.
- Days at 90°F or more
- 22a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 174a normal year
- Days that stay below freezing
- 33high of 32°F or less
- Days with 0.01 inch of precipitation
- 141a normal year
- Days with 1 inch of snow or more
- 22a normal year
The highest temperature in this station's record (since 1965) is 110°F, on July 1, 2021; the lowest is −28°F, on December 31, 1968.
The wettest calendar year on that record is 1996, with 36.48 in; the snowiest season is 1996–97, with 127.7 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00450844; records: ACIS (NOAA Regional Climate Centers), station USC00450844. Records use complete months only; a month missing more than three days is left out.
How sunny is it at Boundary Dam?
Over a year 71% of the sunlight that would reach the ground under clear skies gets through the clouds at Boundary Dam, 3.6 kWh per square metre a day. July is the sunniest month (87%) and December the cloudiest (48%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 50% | 1.0 |
| February | 60% | 1.9 |
| March | 59% | 2.9 |
| April | 65% | 4.4 |
| May | 71% | 5.7 |
| June | 70% | 6.0 |
| July | 87% | 7.2 |
| August | 86% | 5.9 |
| September | 79% | 4.2 |
| October | 68% | 2.4 |
| November | 53% | 1.2 |
| December | 48% | 0.8 |
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 Boundary Dam record?
A normal year at Boundary Dam brings 7,184 heating degree days, 34% more than the median U.S. place (5,373), and 289 cooling degree days, 68% 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 1,839 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,186 | 0 |
| February | 983 | 0 |
| March | 863 | 0 |
| April | 591 | 0 |
| May | 344 | 4 |
| June | 173 | 26 |
| July | 43 | 129 |
| August | 47 | 115 |
| September | 232 | 15 |
| October | 615 | 0 |
| November | 924 | 0 |
| December | 1,184 | 0 |
| Year (annual) | 7,184 | 289 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00450844. 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 Boundary Dam been warmer than normal?
2025 averaged 46.6°F, 0.6°F above the 1991-2020 normal of 46.0°F. 1 of the 2 complete years since 2022 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2022 | 45.0°F | −1.0°F | 25.00 | 83.6 |
| 2025 | 46.6°F | +0.6°F | 26.08 | 18.3 |
Over 33 complete years from 1976 to 2025, the station's annual mean temperature rose at a fitted 4.6°F per century (+0.26°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00450844; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Boundary Dam's climate compare?
Boundary Dam is warmer than 7 of the 96 places with their own NOAA record in Washington, and wetter than 50. Across the 7,247 U.S. stations with normals, its annual mean of 46.0°F is warmer than 23%.
In the Köppen classification computed from these normals, Boundary Dam is Dsb: continental, 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 Boundary Dam share this climate record?
3 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.
- Ione, WA444 people · 18 mi S
- Metaline Falls, WA281 people · 9 mi S
- Metaline, WA164 people · 10 mi S
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 Boundary Dam's climate
What is the coldest month at Boundary Dam?
January, with a normal high of 33°F and a normal low of 21°F. The warmest is July (84°F by day, 52°F at night).
Does it snow at Boundary Dam?
Yes: 55 inches in a normal year, falling on 32 days with 0.1 inch or more, the most in January (18.5 inches).
What is the rainiest month at Boundary Dam?
December, with 3.60 in of precipitation in a normal year; the driest is August with 0.81 in.
What plant hardiness zone is Boundary Dam in?
The USDA's 2023 map puts Boundary Dam in zone 6a in ZIP code 99152, the nearest ZIP area. By the same method at the station, the coldest night of a typical year reaches −4°F (26 years, 1991-2020): zone 6b.
How late can frost come at Boundary Dam?
In half of years the last 32°F night comes after May 4; in one year in ten it comes after May 18. Waiting until May 18 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Washington climateThe statewide normals and every place in the state
- Northport, WA22 miles from this station, 46.4°F a year
- Porthill (1 mi SW), ID39 miles from this station, 47.3°F a year
- Colville, WA40 miles from this station, 48.9°F a year
- Priest River Experiment Station, ID50 miles from this station, 44.7°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made