Prosser, Washington climate: Normal weather by month, frost dates and records
Prosser's normal year runs from 26°F December nights to 90°F July afternoons, with 8.7 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 11.7°C, December lows of −3°C, July highs of 32°C, 222 mm of precipitation a year.
- NOAA stationProsser
- Station IDUSC00456768
- Location46.20°N 119.76°W
- Elevation830 ft (253 m)
- Population6,540
On October 23, the normal high in Prosser is 61°F and the normal low 38°F, and the chance of measurable rain or snow is 20%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Prosser.
- Jan 40° 27°
- Feb 47° 29°
- Mar 56° 35°
- Apr 65° 40°
- May 74° 48°
- Jun 81° 54°
- Jul 90° 60°
- Aug 89° 58°
- Sep 80° 50°
- Oct 65° 41°
- Nov 49° 32°
- Dec 40° 26°
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 Prosser each month?
July is the warmest month, with normal highs of 90°F; December the coldest, with normal lows of 26°F. The most precipitation falls in December (1.33 in), the least in August (0.16 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 40°F | 27°F | 33.5°F | 1.24 | 8 | <1 | 25 | 9 h |
| February | 47°F | 29°F | 37.6°F | 0.90 | 6 | <1 | 21 | 10 h 20 min |
| March | 56°F | 35°F | 45.4°F | 0.69 | 6 | <1 | 12 | 11 h 50 min |
| April | 65°F | 40°F | 52.2°F | 0.74 | 5 | <1 | 4 | 13 h 30 min |
| May | 74°F | 48°F | 61.0°F | 0.88 | 6 | 2 | <1 | 15 h |
| June | 81°F | 54°F | 67.2°F | 0.68 | 4 | 6 | <1 | 15 h 50 min |
| July | 90°F | 60°F | 75.0°F | 0.21 | 2 | 18 | <1 | 15 h 30 min |
| August | 89°F | 58°F | 73.4°F | 0.16 | 2 | 17 | <1 | 14 h 10 min |
| September | 80°F | 50°F | 64.9°F | 0.27 | 3 | 4 | <1 | 12 h 40 min |
| October | 65°F | 41°F | 52.8°F | 0.77 | 6 | <1 | 4 | 11 h |
| November | 49°F | 32°F | 40.5°F | 0.86 | 7 | <1 | 18 | 9 h 30 min |
| December | 40°F | 26°F | 32.9°F | 1.33 | 8 | <1 | 25 | 8 h 40 min |
| Year (annual) | 65°F | 42°F | 53.0°F | 8.73 | 62 | 47 | 109 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 5°C | −3°C | 0.8°C | 31 mm |
| February | 8°C | −2°C | 3.1°C | 23 mm |
| March | 13°C | 2°C | 7.4°C | 18 mm |
| April | 18°C | 4°C | 11.2°C | 19 mm |
| May | 23°C | 9°C | 16.1°C | 22 mm |
| June | 27°C | 12°C | 19.6°C | 17 mm |
| July | 32°C | 15°C | 23.9°C | 5 mm |
| August | 32°C | 14°C | 23.0°C | 4 mm |
| September | 27°C | 10°C | 18.3°C | 7 mm |
| October | 18°C | 5°C | 11.6°C | 20 mm |
| November | 10°C | 0°C | 4.7°C | 22 mm |
| December | 4°C | −3°C | 0.5°C | 34 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Boardman (25 miles away), gets 4 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00456768; 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 Prosser?
Normal highs sit between 65°F and 85°F in May, June and September. Of those, September has the fewest days with rain (3).
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 USC00456768.
When is the last frost in Prosser?
In Prosser, the last spring frost (32°F) comes after April 14 in half of years and after May 7 in one year in ten; the first autumn frost comes before October 22 in half of years and before October 5 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 141 year in 10 after May 7; 9 in 10 after March 24
- First autumn frost, half of years before
- October 221 year in 10 before October 5; 9 in 10 before November 7
NOAA puts the median frost-free season at 189 days, and the season without a hard freeze (28°F) at 224 days.
A hard freeze (28°F) comes after March 23 in half of springs and before November 2 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Prosser in zone 7b in ZIP code 99350, the nearest ZIP area. By the map's own method, the average of each year's coldest night over 1991-2020, Prosser's NOAA station is in zone 7b: the coldest night of a typical year reaches 5°F (15 complete years).
Frost dates for every NOAA station in Washington · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00456768; 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 Prosser?
In a normal year in Prosser, 47 days a year reach 90°F (7 of them 100°F or more), 109 nights fall to 32°F or colder and 62 days bring measurable precipitation.
- Days at 90°F or more
- 47a normal year
- Days at 100°F or more
- 7a normal year
- Nights at 32°F or colder
- 109a normal year
- Days that stay below freezing
- 19high of 32°F or less
- Days with 0.01 inch of precipitation
- 62a normal year
The highest temperature in this station's record (since 1925) is 114°F, on June 30, 2021; the lowest is −20°F, on January 21, 1930.
The wettest calendar year on that record is 1983, with 13.34 in; the snowiest season is 1979–80, with 29.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00456768; records: ACIS (NOAA Regional Climate Centers), station USC00456768. Records use complete months only; a month missing more than three days is left out.
How sunny is Prosser?
Over a year 81% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Prosser, 4.2 kWh per square metre a day. July is the sunniest month (94%) and December the cloudiest (55%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 56% | 1.2 |
| February | 69% | 2.3 |
| March | 72% | 3.6 |
| April | 79% | 5.4 |
| May | 81% | 6.5 |
| June | 85% | 7.2 |
| July | 94% | 7.7 |
| August | 92% | 6.4 |
| September | 87% | 4.7 |
| October | 79% | 3.0 |
| November | 65% | 1.6 |
| December | 55% | 1.0 |
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 Prosser need?
A normal year in Prosser brings 5,172 heating degree days, 4% fewer than the median U.S. place (5,373), and 839 cooling degree days, 8% 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 3,098 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 978 | 0 |
| February | 766 | 0 |
| March | 608 | 0 |
| April | 384 | 2 |
| May | 168 | 44 |
| June | 55 | 122 |
| July | 7 | 316 |
| August | 9 | 271 |
| September | 83 | 80 |
| October | 384 | 4 |
| November | 735 | 0 |
| December | 995 | 0 |
| Year (annual) | 5,172 | 839 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00456768. 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 Prosser been warmer than normal lately?
Over 56 complete years from 1931 to 2020, the station's annual mean temperature rose at a fitted 3.6°F per century (+0.20°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Prosser's climate compare?
Prosser is warmer than 86 of the other 95 places with their own NOAA record in Washington, and wetter than 11. Across the 7,247 U.S. stations with normals, its annual mean of 53.0°F is warmer than 54%.
In the Köppen classification computed from these normals, Prosser 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.
Questions about Prosser's climate
What is the coldest month in Prosser?
December, with a normal high of 40°F and a normal low of 26°F. The warmest is July (90°F by day, 60°F at night).
Does it snow in Prosser?
Yes. NOAA publishes no 1991-2020 snowfall normal for Prosser's NOAA station; the nearest record that keeps one, Boardman (25 miles away), records 4 inches of snow in a normal year.
What is the rainiest month in Prosser?
December, with 1.33 in of precipitation in a normal year; the driest is August with 0.16 in.
What plant hardiness zone is Prosser in?
The USDA's 2023 map puts Prosser in zone 7b in ZIP code 99350, the nearest ZIP area. By the same method at Prosser's NOAA station, the coldest night of a typical year reaches 5°F (15 years, 1991-2020): zone 7b.
How late can frost come in Prosser?
In half of years the last 32°F night comes after April 14; 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
- Sunnyside, WA15 miles from this station, 49.9°F a year
- Boardman, OR25 miles from this station, 54.0°F a year
- Richland, WA25 miles from this station, 53.6°F a year
- McNary Dam, WA29 miles from this station, 54.2°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made