September is one of the warmer months of the year in Bonney Lake, with average highs near 18.7°C and lows around 7.3°C (mean 13°C). It is one of the drier months, averaging 66 mm of rainfall and 73% relative humidity across the period.
September is one of the warmer months of the year in Bonney Lake. Across 45 years of records, the warmest September in Bonney Lake was 2022 — when the month averaged 15.5°C — while the coldest was 1983 at 9.5°C. Typical September days reach 18.7°C with nights near 7.3°C. The long-term trend is warming, about 0.3°C per decade.
September is one of the drier months in Bonney Lake, averaging 66 mm of rainfall. The wettest September on record was 2013 with 236 mm, while the driest was 2012 at 6 mm.
Relative humidity in Bonney Lake during September averages 73%. The most humid September was 2010 at 87%, and the least humid was 1987 at 62%.
September receives about 4 kWh/m²/day of solar energy in Bonney Lake. The sunniest September was 1998 at 4.8 kWh/m²/day, and the cloudiest were 2010, 2013 and 2019 at 3.2.
Average wind speed in Bonney Lake during September is 0.2 m/s. The windiest Septembers were 2017, 2020 and 2023, among others at 0.3 m/s, while the calmest were 2022, 2024 and 2025, among others at 0.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 11.9°C | 13.6°C | 12.9°C | 13.0°C | 14.0°C | +2.1°C |
| Avg High | 17.6°C | 19.5°C | 18.6°C | 18.3°C | 19.8°C | +2.2°C |
| Avg Low | 6.1°C | 7.7°C | 7.2°C | 7.6°C | 8.1°C | +2°C |
| Avg Rain | 77 mm | 51 mm | 57 mm | 81 mm | 65 mm | -12 mm |
September temperatures in Bonney Lake have risen by about 2.7°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -2.8°C (1983) to a record high of 35.2°C (1988).
Rainfall in September is one of the drier months, averaging 66 mm, with a wettest year of 236 mm.
One of the best times to visit Bonney Lake
September is one of the best times to visit Bonney Lake. Expect days averaging 18.7°C and nights around 7.3°C (mean 13°C) — warmer than Bonney Lake's yearly average — with moderate rainfall (66 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 19.7°C | 13.9°C | 8.0°C | 31.0°C | 2.6°C | 52 mm | 76% | 0.2 m/s | 4 |
| 2024 | 19.0°C | 13.1°C | 7.2°C | 32.7°C | -0.8°C | 44 mm | 77% | 0.2 m/s | 3.7 |
| 2023 | 18.5°C | 12.9°C | 7.4°C | 29.3°C | 2.0°C | 84 mm | 74% | 0.3 m/s | 3.9 |
| 2022 🔥 | 21.9°C | 15.5°C | 9.1°C | 32.0°C | 5.3°C | 8 mm | 66% | 0.2 m/s | 4.3 |
| 2021 | 18.8°C | 13.2°C | 7.6°C | 29.9°C | 3.9°C | 106 mm | 73% | 0.2 m/s | 3.8 |
| 2020 | 21.1°C | 15.2°C | 9.4°C | 30.8°C | 6.1°C | 98 mm | 71% | 0.3 m/s | 3.7 |
| 2019 | 16.5°C | 12.1°C | 7.7°C | 30.1°C | -2.4°C | 104 mm | 83% | 0.2 m/s | 3.2 |
| 2018 | 18.0°C | 12.4°C | 6.8°C | 27.4°C | 3.2°C | 52 mm | 74% | 0.2 m/s | 3.9 |
| 2017 | 19.8°C | 14.3°C | 8.9°C | 30.7°C | 3.4°C | 61 mm | 70% | 0.3 m/s | 3.8 |
| 2016 | 16.8°C | 11.8°C | 6.8°C | 26.9°C | 3.3°C | 66 mm | 76% | 0.2 m/s | 4 |
| 2015 | 17.2°C | 11.7°C | 6.1°C | 30.1°C | 1.0°C | 47 mm | 76% | 0.2 m/s | 3.8 |
| 2014 | 19.6°C | 13.9°C | 8.2°C | 29.6°C | 4.8°C | 56 mm | 70% | 0.2 m/s | 4.1 |
| 2013 🌧️ | 17.4°C | 12.9°C | 8.4°C | 31.9°C | 2.6°C | 236 mm | 84% | 0.2 m/s | 3.2 |
| 2012 | 21.0°C | 14.2°C | 7.4°C | 28.0°C | 1.1°C | 6 mm | 66% | 0.3 m/s | 4.6 |
| 2011 | 20.8°C | 14.7°C | 8.6°C | 30.4°C | 3.6°C | 50 mm | 68% | 0.3 m/s | 4 |
| 2010 | 15.9°C | 11.6°C | 7.2°C | 24.4°C | 2.9°C | 129 mm | 87% | 0.2 m/s | 3.2 |
| 2009 | 20.2°C | 13.8°C | 7.5°C | 30.4°C | 1.2°C | 59 mm | 68% | 0.2 m/s | 4.1 |
| 2008 | 19.6°C | 13.3°C | 7.0°C | 31.1°C | 2.1°C | 23 mm | 70% | 0.3 m/s | 4.2 |
| 2007 | 17.0°C | 11.8°C | 6.5°C | 28.4°C | 2.8°C | 47 mm | 76% | 0.2 m/s | 3.7 |
| 2006 | 19.9°C | 13.9°C | 7.8°C | 32.1°C | 2.2°C | 40 mm | 67% | 0.3 m/s | 4.4 |
| 2005 | 16.6°C | 11.4°C | 6.3°C | 23.2°C | 1.7°C | 84 mm | 75% | 0.2 m/s | 4.2 |
| 2004 | 15.1°C | 11.0°C | 7.0°C | 21.8°C | 3.8°C | 114 mm | 86% | 0.2 m/s | 3.6 |
| 2003 | 21.2°C | 14.7°C | 8.1°C | 32.7°C | 3.4°C | 50 mm | 67% | 0.2 m/s | 4.2 |
| 2002 | 19.2°C | 13.2°C | 7.2°C | 28.4°C | 1.5°C | 23 mm | 68% | 0.3 m/s | 4.3 |
| 2001 | 19.6°C | 13.5°C | 7.5°C | 27.7°C | 1.2°C | 23 mm | 71% | 0.3 m/s | 4 |
| 2000 | 17.2°C | 12.0°C | 6.8°C | 28.5°C | -1.9°C | 104 mm | 76% | 0.2 m/s | 3.9 |
| 1999 | 19.2°C | 13.0°C | 6.7°C | 27.8°C | 0.6°C | 15 mm | 67% | 0.3 m/s | 4.7 |
| 1998 | 21.1°C | 15.0°C | 8.9°C | 30.4°C | 5.0°C | 23 mm | 70% | 0.3 m/s | 4.8 |
| 1997 | 18.7°C | 13.3°C | 7.8°C | 29.9°C | 3.2°C | 123 mm | 80% | 0.2 m/s | 3.8 |
| 1996 | 15.5°C | 10.7°C | 6.0°C | 27.2°C | -0.3°C | 86 mm | 81% | 0.2 m/s | 3.6 |
| 1995 | 20.2°C | 14.5°C | 8.7°C | 28.3°C | 5.4°C | 74 mm | 73% | 0.2 m/s | 3.9 |
| 1994 | 20.4°C | 14.4°C | 8.5°C | 28.9°C | 2.8°C | 57 mm | 71% | 0.3 m/s | 4.1 |
| 1993 | 20.0°C | 13.8°C | 7.7°C | 27.4°C | 1.0°C | 8 mm | 66% | 0.3 m/s | 4.7 |
| 1992 | 16.8°C | 11.4°C | 6.0°C | 24.9°C | -0.4°C | 107 mm | 74% | 0.2 m/s | 4.1 |
| 1991 | 20.9°C | 14.5°C | 8.1°C | 29.0°C | 3.5°C | 8 mm | 68% | 0.2 m/s | 4.4 |
| 1990 | 22.2°C | 15.3°C | 8.4°C | 28.1°C | 4.0°C | 10 mm | 68% | 0.3 m/s | 4 |
| 1989 | 20.9°C | 13.9°C | 7.0°C | 28.3°C | 2.8°C | 17 mm | 63% | 0.3 m/s | 4.5 |
| 1988 | 19.1°C | 12.7°C | 6.3°C | 35.2°C | 0.5°C | 93 mm | 69% | 0.3 m/s | 4 |
| 1987 | 22.1°C | 15.2°C | 8.2°C | 30.4°C | 1.6°C | 24 mm | 62% | 0.3 m/s | 4.2 |
| 1986 | 15.0°C | 10.2°C | 5.4°C | 25.8°C | 2.3°C | 120 mm | 79% | 0.2 m/s | 3.5 |
| 1985 | 15.2°C | 10.0°C | 4.7°C | 22.3°C | 0.5°C | 92 mm | 74% | 0.2 m/s | 3.8 |
| 1984 | 16.1°C | 10.7°C | 5.3°C | 23.6°C | -1.7°C | 74 mm | 74% | 0.2 m/s | 3.7 |
| 1983 ❄️ | 14.4°C | 9.5°C | 4.6°C | 21.1°C | -2.8°C | 82 mm | 80% | 0.2 m/s | — |
| 1982 | 17.4°C | 11.9°C | 6.3°C | 27.0°C | 0.9°C | 106 mm | 78% | 0.2 m/s | — |
| 1981 | 18.3°C | 12.7°C | 7.0°C | 32.2°C | 2.5°C | 86 mm | 74% | 0.2 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 18.7°C with lows near 7.3°C (mean 13°C), based on 45 years of NASA POWER data.
September averages 66 mm of rainfall in Bonney Lake, one of the drier months. The wettest on record was 236 mm in 2013.
The hottest September reached 35.2°C in 1988. The coldest dipped to -2.8°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2.7°C. Daytime highs moved from 16.3°C to 19.6°C and overnight lows from 5.6°C to 7.9°C over the same span.
September is one of the warmer months of the year in Bonney Lake and one of the drier months, so plan for around 18.7°C daytime highs and 7.3°C at night.
Not quite — September is the 10th coolest month in Bonney Lake, averaging 13°C.
For September in Bonney Lake, pack warm layers and a jacket for chilly mornings, with typical highs of 18.7°C and lows of 7.3°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 73% — moderately humid.
Average wind speed in September is 0.2 m/s. The windiest September on record averaged 0.3 m/s (1987).
The wettest September on record was 2013 with 236 mm. On average, September sees 66 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Bonney Lake behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
