Climate averages 1991–2020
Tri-Cities weather
in September.
A warm, very dry month: the 4th warmest and the 3rd driest of the year. Meets the pleasant-weather rule
Long-term climate patterns, not a forecast for a particular trip.
September is a warm month in Tri-Cities: daytime highs average 27.5°C and nights cool to about 14.0°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 6.9 mm of rain on roughly 2 days, which makes September a very dry month (the 3rd driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 36 min on an average September day.
The nearest other city in this atlas is Kennewick (6 km away). In September its highs average 27.4°C, about as warm as Tri-Cities, with 6.9 mm of rain.
Among the 498 cities listed in the United States, Tri-Cities ranks joint 223rd of 498 for the warmest September highs and joint 97th of 498 for the driest September (rainfall, lowest first). The mean September high of those 498 cities is 26.9°C; Tri-Cities is 0.6°C warmer than that mean.
From September to October, average highs fall by 8.6°C to 18.9°C, and monthly rainfall rises from 6.9 mm to 22 mm.
The annual picture
September in context
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, selected | 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
September in nearby cities
- Kennewick in SeptemberUnited States · 6 kmHigh 27.4°C · Low 13.9°C · 6.9 mm rain
- Yakima in SeptemberUnited States · 108 kmHigh 24.9°C · Low 10.7°C · 8.4 mm rain
- Spokane in SeptemberUnited States · 207 kmHigh 23.7°C · Low 11.0°C · 19 mm rain
- Spokane Valley in SeptemberUnited States · 217 kmHigh 23.2°C · Low 10.5°C · 22 mm rain
- Auburn in SeptemberUnited States · 259 kmHigh 20.8°C · Low 11.3°C · 64 mm rain
- Kent in SeptemberUnited States · 263 kmHigh 21.2°C · Low 11.8°C · 67 mm rain
- Gresham in SeptemberUnited States · 264 kmHigh 22.8°C · Low 11.3°C · 58 mm rain
- Federal Way in SeptemberUnited States · 266 kmHigh 20.3°C · Low 11.2°C · 64 mm rain
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 limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Tri-Cities) is explained once on the Tri-Cities year overview and on the Sources, method and limits page.
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.