September is one of the warmer months of the year in Lynnwood, with average highs near 20.2°C and lows around 10.9°C (mean 15.6°C). It is one of the drier months, averaging 58 mm of rainfall and 77% relative humidity across the period.
September is one of the warmer months of the year in Lynnwood. Across 45 years of records, the warmest September in Lynnwood was 2020 — when the month averaged 17.4°C — while the coldest was 1983 at 13.5°C. Typical September days reach 20.2°C with nights near 10.9°C. The long-term September temperature trend is broadly flat.
September is one of the drier months in Lynnwood, averaging 58 mm of rainfall. The wettest September on record was 2013 with 156 mm, while the driest was 2022 at 5 mm.
Relative humidity in Lynnwood during September averages 77%. The most humid September was 2025 at 89%, and the least humid was 1989 at 69%.
September receives about 4 kWh/m²/day of solar energy in Lynnwood. 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 Lynnwood during September is 0.5 m/s. The windiest Septembers were 2020, 2021 and 2023, among others at 0.5 m/s, while the calmest were 2022, 2024 and 2025, among others at 0.4 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 15.0°C | 16.0°C | 15.3°C | 15.6°C | 15.9°C | +0.9°C |
| Avg High | 19.9°C | 20.9°C | 20.0°C | 20.1°C | 20.3°C | +0.4°C |
| Avg Low | 10.1°C | 11.3°C | 10.7°C | 11.2°C | 11.5°C | +1.4°C |
| Avg Rain | 60 mm | 44 mm | 50 mm | 70 mm | 73 mm | +13 mm |
September temperatures in Lynnwood have risen by about 1.1°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 3.2°C (1983) to a record high of 34.1°C (1988).
Rainfall in September is one of the drier months, averaging 58 mm, with a wettest year of 156 mm.
Daytime highs and overnight lows have shifted differently — highs rose about 0°C per decade while lows rose 0.3°C per decade, narrowing the gap between day and night.
One of the best times to visit Lynnwood
September is one of the best times to visit Lynnwood. Expect days averaging 20.2°C and nights around 10.9°C (mean 15.6°C) — warmer than Lynnwood's yearly average — with moderate rainfall (58 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 | 18.1°C | 14.4°C | 10.8°C | 26.2°C | 7.5°C | 106 mm | 89% | 0.4 m/s | 4 |
| 2024 | 19.0°C | 14.9°C | 10.8°C | 33.4°C | 5.7°C | 55 mm | 85% | 0.4 m/s | 3.7 |
| 2023 | 20.0°C | 15.6°C | 11.3°C | 26.7°C | 6.0°C | 77 mm | 80% | 0.5 m/s | 3.9 |
| 2022 | 22.0°C | 17.2°C | 12.3°C | 29.3°C | 9.5°C | 5 mm | 76% | 0.4 m/s | 4.3 |
| 2021 | 20.3°C | 15.7°C | 11.1°C | 26.5°C | 8.8°C | 116 mm | 79% | 0.5 m/s | 3.8 |
| 2020 🔥 | 22.1°C | 17.4°C | 12.7°C | 34.1°C | 9.3°C | 81 mm | 78% | 0.5 m/s | 3.7 |
| 2019 | 19.5°C | 15.5°C | 11.6°C | 27.0°C | 5.1°C | 96 mm | 81% | 0.5 m/s | 3.2 |
| 2018 | 19.2°C | 14.8°C | 10.5°C | 27.9°C | 7.7°C | 63 mm | 81% | 0.5 m/s | 3.9 |
| 2017 | 20.9°C | 16.5°C | 12.1°C | 28.6°C | 7.9°C | 35 mm | 77% | 0.5 m/s | 3.8 |
| 2016 | 19.2°C | 14.9°C | 10.6°C | 25.5°C | 8.0°C | 47 mm | 79% | 0.5 m/s | 4 |
| 2015 | 18.9°C | 14.5°C | 10.0°C | 26.7°C | 6.4°C | 52 mm | 80% | 0.5 m/s | 3.8 |
| 2014 | 21.9°C | 16.9°C | 12.0°C | 31.8°C | 8.5°C | 70 mm | 76% | 0.5 m/s | 4.1 |
| 2013 🌧️ | 20.4°C | 16.3°C | 12.1°C | 33.0°C | 7.8°C | 156 mm | 83% | 0.5 m/s | 3.2 |
| 2012 | 20.8°C | 15.7°C | 10.7°C | 29.2°C | 6.4°C | 6 mm | 74% | 0.5 m/s | 4.6 |
| 2011 | 21.0°C | 16.3°C | 11.7°C | 26.8°C | 9.1°C | 43 mm | 77% | 0.5 m/s | 4 |
| 2010 | 19.0°C | 15.0°C | 10.9°C | 24.8°C | 8.4°C | 130 mm | 86% | 0.5 m/s | 3.2 |
| 2009 | 21.6°C | 16.3°C | 11.1°C | 30.9°C | 6.2°C | 61 mm | 75% | 0.5 m/s | 4.1 |
| 2008 | 20.4°C | 15.4°C | 10.4°C | 31.3°C | 6.7°C | 22 mm | 75% | 0.4 m/s | 4.2 |
| 2007 | 18.4°C | 14.3°C | 10.2°C | 26.4°C | 4.9°C | 58 mm | 80% | 0.5 m/s | 3.7 |
| 2006 | 20.7°C | 15.9°C | 11.1°C | 31.6°C | 6.7°C | 38 mm | 73% | 0.5 m/s | 4.4 |
| 2005 | 18.8°C | 14.5°C | 10.1°C | 22.6°C | 7.2°C | 62 mm | 77% | 0.4 m/s | 4.2 |
| 2004 | 18.3°C | 14.5°C | 10.7°C | 22.0°C | 7.0°C | 89 mm | 83% | 0.5 m/s | 3.6 |
| 2003 | 21.4°C | 16.4°C | 11.5°C | 29.2°C | 7.3°C | 35 mm | 74% | 0.4 m/s | 4.2 |
| 2002 | 19.9°C | 15.1°C | 10.4°C | 25.3°C | 5.9°C | 29 mm | 75% | 0.5 m/s | 4.3 |
| 2001 | 20.3°C | 15.7°C | 11.0°C | 26.0°C | 7.1°C | 23 mm | 77% | 0.4 m/s | 4 |
| 2000 | 20.0°C | 15.3°C | 10.6°C | 28.0°C | 6.3°C | 78 mm | 77% | 0.5 m/s | 3.9 |
| 1999 | 19.9°C | 14.9°C | 9.9°C | 27.2°C | 5.8°C | 13 mm | 75% | 0.5 m/s | 4.7 |
| 1998 | 21.2°C | 16.5°C | 11.7°C | 25.8°C | 8.7°C | 18 mm | 77% | 0.4 m/s | 4.8 |
| 1997 | 20.9°C | 16.6°C | 12.3°C | 29.0°C | 9.1°C | 133 mm | 81% | 0.5 m/s | 3.8 |
| 1996 | 18.4°C | 14.2°C | 10.1°C | 25.0°C | 4.7°C | 83 mm | 80% | 0.4 m/s | 3.6 |
| 1995 | 21.7°C | 16.9°C | 12.2°C | 26.0°C | 8.3°C | 51 mm | 77% | 0.5 m/s | 3.9 |
| 1994 | 22.0°C | 17.0°C | 12.0°C | 26.9°C | 8.7°C | 43 mm | 75% | 0.4 m/s | 4.1 |
| 1993 | 21.7°C | 16.4°C | 11.2°C | 29.7°C | 5.8°C | 10 mm | 71% | 0.4 m/s | 4.7 |
| 1992 | 18.9°C | 14.3°C | 9.7°C | 25.8°C | 5.8°C | 70 mm | 76% | 0.5 m/s | 4.1 |
| 1991 | 21.4°C | 16.4°C | 11.4°C | 29.1°C | 7.8°C | 6 mm | 76% | 0.4 m/s | 4.4 |
| 1990 | 22.4°C | 17.2°C | 12.1°C | 29.6°C | 9.1°C | 10 mm | 73% | 0.5 m/s | 4 |
| 1989 | 22.5°C | 16.7°C | 10.9°C | 28.8°C | 8.0°C | 10 mm | 69% | 0.4 m/s | 4.5 |
| 1988 | 20.7°C | 15.5°C | 10.2°C | 34.1°C | 6.4°C | 77 mm | 72% | 0.5 m/s | 4 |
| 1987 | 22.2°C | 16.7°C | 11.3°C | 28.7°C | 7.9°C | 19 mm | 70% | 0.4 m/s | 4.2 |
| 1986 | 18.2°C | 13.9°C | 9.6°C | 24.2°C | 7.0°C | 72 mm | 77% | 0.5 m/s | 3.5 |
| 1985 | 18.8°C | 14.0°C | 9.2°C | 22.9°C | 5.7°C | 71 mm | 74% | 0.5 m/s | 3.8 |
| 1984 | 18.5°C | 13.9°C | 9.3°C | 22.6°C | 5.7°C | 70 mm | 78% | 0.5 m/s | 3.7 |
| 1983 ❄️ | 18.1°C | 13.5°C | 8.8°C | 24.8°C | 3.2°C | 80 mm | 78% | 0.5 m/s | — |
| 1982 | 20.3°C | 15.6°C | 10.9°C | 30.9°C | 7.0°C | 57 mm | 78% | 0.5 m/s | — |
| 1981 | 20.2°C | 15.3°C | 10.5°C | 33.1°C | 6.6°C | 88 mm | 78% | 0.5 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 20.2°C with lows near 10.9°C (mean 15.6°C), based on 45 years of NASA POWER data.
September averages 58 mm of rainfall in Lynnwood, one of the drier months. The wettest on record was 156 mm in 2013.
The hottest September reached 34.1°C in 1988. The coldest dipped to 3.2°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.1°C. Daytime highs moved from 19.2°C to 19.9°C and overnight lows from 9.7°C to 11.3°C over the same span.
September is one of the warmer months of the year in Lynnwood and one of the drier months, so plan for around 20.2°C daytime highs and 10.9°C at night.
Not quite — September is the 10th coolest month in Lynnwood, averaging 15.6°C.
For September in Lynnwood, pack light layers you can adjust through the day, with typical highs of 20.2°C and lows of 10.9°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 77% — quite humid.
Average wind speed in September is 0.5 m/s. The windiest September on record averaged 0.5 m/s (1981).
The wettest September on record was 2013 with 156 mm. On average, September sees 58 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 Lynnwood 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.
