Climate averages 1991–2020
Tri-Cities weather
by month.
See how the year changes. July has the highest average daily maximum; July has the lowest average monthly rainfall.
Pleasant-weather months by our simple rule: AprilMayJuneSeptemberOctober
Long-term climate patterns, not a forecast for a particular trip.
Across the year Tri-Cities averages a daytime high of 19.4°C and a nighttime low of 7.9°C, with about 228 mm of rain on roughly 57 days. July is the warmest month (average high 34.2°C) and December the coolest (5.6°C). December is the wettest month with 35 mm; July is the driest with 3.8 mm.
Months with pleasant weather by a simple rule (average high between 18°C and 29°C, average low of at least 5°C and at most 8 rain days): April, May, June, September and October. This looks at temperature and rain only, not humidity, wind, sea temperature or crowds.
The annual picture
A year in Tri-Cities
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Tri-Cities climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 6.0°C-1.5°C | -1.5°C | 34 | 8.1 | 9.19 h |
| February | 9.3°C-0.3°C | -0.3°C | 23 | 6.2 | 10.310 h |
| March | 14.3°C2.8°C | 2.8°C | 24 | 5.9 | 11.912 h |
| April | 19.3°C6.6°C | 6.6°C | 17 | 4.9 | 13.514 h |
| May | 25.0°C11.5°C | 11.5°C | 18 | 4.5 | 15.015 h |
| June | 28.9°C15.3°C | 15.3°C | 13 | 2.8 | 15.716 h |
| July | 34.2°C19.2°C | 19.2°C | 3.8 | 1.0 | 15.415 h |
| August | 33.2°C18.6°C | 18.6°C | 4.2 | 1.0 | 14.214 h |
| September | 27.5°C14.0°C | 14.0°C | 6.9 | 1.8 | 12.613 h |
| October | 18.9°C7.9°C | 7.9°C | 22 | 5.0 | 11.011 h |
| November | 10.7°C2.3°C | 2.3°C | 29 | 7.3 | 9.59 h |
| December | 5.6°C-1.2°C | -1.2°C | 35 | 8.4 | 8.79 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
Nearby cities
- KennewickUnited States · 6 kmHigh 19.2°C · Low 7.8°C · 228 mm rain a year
- YakimaUnited States · 108 kmHigh 16.3°C · Low 4.7°C · 341 mm rain a year
- SpokaneUnited States · 207 kmHigh 15.1°C · Low 4.7°C · 551 mm rain a year
- Spokane ValleyUnited States · 217 kmHigh 14.6°C · Low 4.2°C · 619 mm rain a year
- AuburnUnited States · 259 kmHigh 14.8°C · Low 6.7°C · 1,375 mm rain a year
- KentUnited States · 263 kmHigh 15.2°C · Low 7.1°C · 1,316 mm rain a year
- GreshamUnited States · 264 kmHigh 15.6°C · Low 6.5°C · 1,567 mm rain a year
- Federal WayUnited States · 266 kmHigh 14.3°C · Low 6.4°C · 1,375 mm rain a year
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsWhat do the high and low temperatures mean?
We average the daily maximum and daily minimum for each calendar month over 1991–2020. They are not record extremes, a forecast range or temperatures at a fixed time of day.
How is a rain day counted?
A local calendar day (standard time, UTC-8, no daylight saving) with at least 1 mm of total precipitation counts as one rain day. We count these for each year and month, then average across 30 years. The average does not predict which days will be wet.
Where do the numbers come from?
ERA5-Land (temperature) and ERA5 (precipitation) reanalysis from the Copernicus Climate Change Service, read from the Open-Meteo open-data archive. Temperature comes from the 0.1° model cell at 46.20°, -119.20° (5 km from the city centre), adjusted up by 1.0°C for the difference between the city's elevation (106 m) and the cell's (263 m). Rain comes from the 0.25° cell at 46.25°, -119.25°. Kennewick lies in the same rainfall cell, so its rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells. These are model estimates, not weather-station readings; coast, hills and city streets can differ.
Does this page show sunshine, humidity or sea temperature?
No. The data used here contain air temperature and precipitation only. Daylight hours are calculated from the city's latitude (sunrise to sunset), not measured sunshine.