Prosser, Washington Weather
Pikas hayfeeding in granite peaks. Day 77 of spring. Read this microseason across nine climate regions →
Prosser weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 4Overcast——79°55°—
- FridayJun 5Overcast——73°54°-6°
- SaturdayJun 6Overcast——69°48°-4°
- SundayJun 7Overcast——73°44°+4°
- MondayJun 8Light Drizzle—0.02″77°52°+4°
- TuesdayJun 9Heavy Drizzle26%0.13″74°56°-3°
- WednesdayJun 10Mostly Clear12%—86°56°+12°
Ozone at AQI 42 now. AQI flat over the last 6 hours (within ±3 points). With UV 8.0 peaking around 1 PM under partly cloudy skies, surface ozone likely climbs to AQI 32 by mid-afternoon.
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion.
What's driving it
Ozone × UV × Sky
Ozone at AQI 42 now. With UV 8.0 peaking around 1 PM under partly cloudy skies, surface ozone likely climbs to AQI 32 by mid-afternoon.
- Present
- AQI 42
- UV peak
- 8.0 at 1 PM
- Sky at peak
- partly cloudy
- Projected peak
- AQI 32
Trends
Seven days of AQI and PM2.5.
Hourly air-quality data from the Copernicus Atmosphere Monitoring Service, charted across the past and next several days. Dashed lines mark the AQI breakpoints at 50 (Good → Moderate) and 100 (Moderate → Unhealthy for Sensitive Groups).
A summer fog for fair, a winter fog for rain.
- Moonrise
- 6:53 AM
- Moonset
- 3:45 PM
- In sign
- ♒︎ Aquarius
Pikas hayfeeding in granite peaks
Prosser at a glance
- Today vs. normal: 6°F above the seasonal normal for this latitude
- Last frost: May 23 (climatological average for this latitude)
- Microseason: Jun 1–5
- Planting window: Harvest spring lettuce before it bolts. Sow heat-tolerant greens.
Right now in the garden
Warm-season window is open
As of June 4, the last spring frost has passed for most years. Transplant tomatoes, peppers, eggplants, basil, and cucurbits (cucumbers, squash, melons) now. Direct-sow beans and corn into warm soil.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | — | — |
| February | — | — |
| March | — | — |
| April | — | — |
| May | lettuce, peas, spinach, radishes | lettuce, peas, radishes |
| June | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| July | tomatoes, peppers, beans, squash | tomatoes, beans, summer squash |
| August | tomatoes, peppers, beans, squash, fall brassicas, garlic (overwinter), carrots | tomatoes, beans, summer squash |
| September | fall brassicas, garlic (overwinter), carrots | tomatoes, beans, summer squash |
| October | — | winter squash, tomatoes (last) |
| November | — | — |
| December | — | — |
A year in weather
Prosser's warmest month is July (~75°F mean) and its coldest is December (~33°F). Rainfall peaks in December (1.3 inches) and bottoms out in August (0.2 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 34° | 1.2″ | 4 |
| February | 38° | 0.9″ | 3 |
| March | 45° | 0.7″ | 3 |
| April | 52° | 0.7″ | 2 |
| May | 61° | 0.9″ | 2 |
| June | 67° | 0.7″ | 2 |
| July | 75° | 0.2″ | 1 |
| August | 73° | 0.2″ | 1 |
| September | 65° | 0.3″ | 1 |
| October | 53° | 0.8″ | 3 |
| November | 41° | 0.9″ | 3 |
| December | 33° | 1.3″ | 4 |
Regional context
Prosser's climate, per the NOAA NCEI 1991-2020 normals from the nearest reporting station, runs cold-winter and warm-summer. January means hover near 34°F while July climbs to 75°F — a 42°F seasonal swing typical of northern-tier latitudes. Annual precipitation totals about 8.7 inches spread across roughly 29 days with measurable rain or snow.
Precipitation peaks in the cool season: December averages 1.3 inches across 4.2 days with measurable rain, mostly from frontal systems and winter storms, while August bottoms out at 0.2 inches across just 0.8 rainy days during the drier warm-season stretch. That winter-storm-driven distribution puts Prosser alongside places like Grandview, WA, Mabton, WA and Sunnyside, WA, all of which run drier through the summer months and rely on cool-season frontal activity for the year's precipitation.
The frost-sensitive growing window opens around late-May, when overnight lows reliably clear freezing for cool-season crops like peas, lettuce, spinach, and radishes. Heat-loving transplants like tomatoes, peppers, and squash generally hold off for another 10-14 days to clear the last spring frost risk window. The window closes around early-October, when overnight lows resume dipping below freezing and frost-tender plants need protection or harvest. These are 30-year central tendencies; year-to-year frost dates can move by up to two weeks. Local features matter: a south-facing slope inside Prosser typically runs 3-5 days ahead of the regional last-frost date, while a low-lying lot along a creek or drainage can lag the same date by a week or more on calm clear nights.
Similar climates: Grandview, WA, Mabton, WA, Sunnyside, WA, Benton City, WA, Outlook, WA.
Frequently asked
- When does it freeze in Prosser?
- Prosser's last spring frost typically falls around mid-May, and the first fall frost arrives around mid-October.
- What is the rainy season in Prosser?
- December is the wettest month with about 1.3 inches of rain on average; the city receives roughly 9 inches annually.
- What is the warmest month in Prosser?
- July is typically warmest, averaging about 75°F.
- What is the coldest month in Prosser?
- December is typically coldest, averaging about 33°F.
- When can I start a vegetable garden in Prosser?
- Cool-season crops (peas, lettuce) can be sown around the last spring frost (mid-May); warm-season crops (tomatoes, peppers) wait until 1–2 weeks after.
- How many rainy days does Prosser get?
- Prosser averages about 29 rainy days per year.
- What hardiness zone is Prosser?
- Prosser's USDA hardiness zone is determined by its lowest average winter temperature; check the USDA's online lookup with the city ZIP for the current zone designation.
Climate
Prosser, Washington sits in a warm-summer Mediterranean climate zone. January means hover near 34°F while July averages 75°F — a 42°F seasonal swing.
Across the year, Prosser receives about 9 inches of precipitation spread over roughly 29 rainy days.
The rhythm of the year is set by latitude (46.2°N), proximity to large water bodies, and elevation — all of which shape what grows here, when frost is likely, and what the weather story looks like day to day.