September is one of the warmer months of the year in Snohomish, with average highs near 19°C and lows around 9.3°C (mean 14.2°C). It is one of the drier months, averaging 83 mm of rainfall and 79% relative humidity across the period.
September is one of the warmer months of the year in Snohomish. Across 45 years of records, the warmest Septembers in Snohomish were 1990 and 2020 — when the month averaged 16.3°C — while the coldest was 1983 at 11.5°C. Typical September days reach 19°C with nights near 9.3°C. The long-term trend is warming, about 0.2°C per decade.
September is one of the drier months in Snohomish, averaging 83 mm of rainfall. The wettest September on record was 2013 with 224 mm, while the driest was 2022 at 9 mm.
Relative humidity in Snohomish during September averages 79%. The most humid September was 2025 at 89%, and the least humid was 1987 at 70%.
September receives about 4 kWh/m²/day of solar energy in Snohomish. 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 Snohomish during September is 0.3 m/s. The windiest Septembers were 1990, 1993 and 2012 at 0.4 m/s, while the calmest were 2019, 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 | 13.3°C | 14.8°C | 13.9°C | 14.3°C | 14.8°C | +1.5°C |
| Avg High | 18.4°C | 19.9°C | 18.7°C | 18.9°C | 19.5°C | +1.1°C |
| Avg Low | 8.3°C | 9.7°C | 9.2°C | 9.7°C | 10.0°C | +1.7°C |
| Avg Rain | 88 mm | 64 mm | 76 mm | 97 mm | 97 mm | +9 mm |
September temperatures in Snohomish have risen by about 1.8°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 0.4°C (1983) to a record high of 35.2°C (1988).
Rainfall in September is one of the drier months, averaging 83 mm, with a wettest year of 224 mm.
One of the best times to visit Snohomish
September is one of the best times to visit Snohomish. Expect days averaging 19°C and nights around 9.3°C (mean 14.2°C) — warmer than Snohomish's yearly average — with higher rainfall (83 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 | 17.8°C | 13.8°C | 9.7°C | 27.1°C | 5.5°C | 121 mm | 89% | 0.2 m/s | 4 |
| 2024 | 18.3°C | 13.8°C | 9.3°C | 33.6°C | 2.8°C | 66 mm | 86% | 0.2 m/s | 3.7 |
| 2023 | 19.1°C | 14.3°C | 9.6°C | 27.6°C | 3.0°C | 95 mm | 80% | 0.3 m/s | 3.9 |
| 2022 | 21.4°C | 16.1°C | 10.8°C | 30.2°C | 7.5°C | 9 mm | 76% | 0.3 m/s | 4.3 |
| 2021 | 18.9°C | 14.3°C | 9.7°C | 27.1°C | 6.1°C | 170 mm | 80% | 0.3 m/s | 3.8 |
| 2020 | 21.3°C | 16.3°C | 11.2°C | 32.8°C | 7.7°C | 121 mm | 80% | 0.3 m/s | 3.7 |
| 2019 | 17.6°C | 13.8°C | 9.9°C | 28.5°C | 1.2°C | 125 mm | 85% | 0.2 m/s | 3.2 |
| 2018 | 18.0°C | 13.5°C | 9.0°C | 27.6°C | 6.0°C | 83 mm | 81% | 0.3 m/s | 3.9 |
| 2017 | 20.4°C | 15.6°C | 10.8°C | 29.7°C | 5.4°C | 54 mm | 75% | 0.3 m/s | 3.8 |
| 2016 | 17.5°C | 13.3°C | 9.0°C | 24.9°C | 5.5°C | 77 mm | 82% | 0.3 m/s | 4 |
| 2015 | 17.5°C | 13.0°C | 8.4°C | 28.5°C | 3.8°C | 74 mm | 81% | 0.3 m/s | 3.8 |
| 2014 | 20.4°C | 15.3°C | 10.2°C | 31.0°C | 5.6°C | 94 mm | 78% | 0.3 m/s | 4.1 |
| 2013 🌧️ | 19.0°C | 14.8°C | 10.5°C | 33.1°C | 5.4°C | 224 mm | 86% | 0.2 m/s | 3.2 |
| 2012 | 20.6°C | 15.0°C | 9.4°C | 29.4°C | 3.4°C | 11 mm | 73% | 0.4 m/s | 4.6 |
| 2011 | 20.6°C | 15.5°C | 10.4°C | 29.3°C | 6.8°C | 63 mm | 76% | 0.3 m/s | 4 |
| 2010 | 17.4°C | 13.4°C | 9.5°C | 24.5°C | 6.3°C | 170 mm | 88% | 0.2 m/s | 3.2 |
| 2009 | 20.2°C | 15.0°C | 9.8°C | 30.3°C | 3.4°C | 91 mm | 77% | 0.3 m/s | 4.1 |
| 2008 | 19.6°C | 14.1°C | 8.7°C | 30.9°C | 2.7°C | 33 mm | 77% | 0.3 m/s | 4.2 |
| 2007 | 17.1°C | 12.8°C | 8.4°C | 28.1°C | 4.0°C | 74 mm | 82% | 0.3 m/s | 3.7 |
| 2006 | 19.8°C | 14.8°C | 9.9°C | 31.6°C | 4.8°C | 56 mm | 74% | 0.3 m/s | 4.4 |
| 2005 | 16.9°C | 12.7°C | 8.4°C | 21.4°C | 5.0°C | 104 mm | 80% | 0.3 m/s | 4.2 |
| 2004 | 16.4°C | 12.7°C | 9.0°C | 21.8°C | 5.0°C | 151 mm | 87% | 0.2 m/s | 3.6 |
| 2003 | 20.8°C | 15.5°C | 10.2°C | 30.3°C | 5.7°C | 54 mm | 73% | 0.3 m/s | 4.2 |
| 2002 | 18.7°C | 13.8°C | 8.9°C | 25.5°C | 4.0°C | 44 mm | 77% | 0.3 m/s | 4.3 |
| 2001 | 18.9°C | 14.2°C | 9.6°C | 26.3°C | 4.8°C | 32 mm | 79% | 0.3 m/s | 4 |
| 2000 | 18.1°C | 13.3°C | 8.6°C | 27.7°C | 1.8°C | 124 mm | 81% | 0.3 m/s | 3.9 |
| 1999 | 19.4°C | 13.9°C | 8.4°C | 28.3°C | 2.3°C | 28 mm | 74% | 0.3 m/s | 4.7 |
| 1998 | 20.6°C | 15.6°C | 10.6°C | 27.2°C | 6.5°C | 25 mm | 76% | 0.3 m/s | 4.8 |
| 1997 | 20.0°C | 15.1°C | 10.3°C | 30.7°C | 6.4°C | 175 mm | 83% | 0.3 m/s | 3.8 |
| 1996 | 16.7°C | 12.4°C | 8.1°C | 27.6°C | 2.2°C | 114 mm | 84% | 0.3 m/s | 3.6 |
| 1995 | 20.9°C | 15.8°C | 10.8°C | 28.0°C | 6.2°C | 74 mm | 77% | 0.3 m/s | 3.9 |
| 1994 | 20.6°C | 15.6°C | 10.6°C | 27.7°C | 6.2°C | 64 mm | 76% | 0.3 m/s | 4.1 |
| 1993 | 20.6°C | 15.2°C | 9.8°C | 28.6°C | 2.7°C | 17 mm | 73% | 0.4 m/s | 4.7 |
| 1992 | 17.0°C | 12.5°C | 7.9°C | 25.4°C | 2.6°C | 120 mm | 80% | 0.3 m/s | 4.1 |
| 1991 | 20.7°C | 15.3°C | 9.9°C | 29.0°C | 5.0°C | 10 mm | 76% | 0.3 m/s | 4.4 |
| 1990 🔥 | 22.0°C | 16.3°C | 10.7°C | 28.6°C | 7.1°C | 15 mm | 73% | 0.4 m/s | 4 |
| 1989 | 21.3°C | 15.2°C | 9.1°C | 28.5°C | 4.8°C | 17 mm | 71% | 0.3 m/s | 4.5 |
| 1988 | 19.2°C | 13.8°C | 8.3°C | 35.2°C | 2.8°C | 121 mm | 76% | 0.3 m/s | 4 |
| 1987 | 21.5°C | 15.9°C | 10.3°C | 29.1°C | 4.9°C | 32 mm | 70% | 0.3 m/s | 4.2 |
| 1986 | 15.9°C | 11.7°C | 7.5°C | 23.7°C | 3.8°C | 109 mm | 81% | 0.3 m/s | 3.5 |
| 1985 | 17.1°C | 11.9°C | 6.7°C | 23.9°C | 3.1°C | 109 mm | 77% | 0.3 m/s | 3.8 |
| 1984 | 16.9°C | 12.2°C | 7.5°C | 22.7°C | 2.6°C | 98 mm | 79% | 0.3 m/s | 3.7 |
| 1983 ❄️ | 16.2°C | 11.5°C | 6.8°C | 23.1°C | 0.4°C | 101 mm | 81% | 0.3 m/s | — |
| 1982 | 19.0°C | 14.0°C | 9.1°C | 30.5°C | 4.0°C | 93 mm | 80% | 0.3 m/s | — |
| 1981 | 18.9°C | 13.9°C | 9.0°C | 32.1°C | 4.3°C | 116 mm | 80% | 0.3 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 19°C with lows near 9.3°C (mean 14.2°C), based on 45 years of NASA POWER data.
September averages 83 mm of rainfall in Snohomish, one of the drier months. The wettest on record was 224 mm in 2013.
The hottest September reached 35.2°C in 1988. The coldest dipped to 0.4°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.8°C. Daytime highs moved from 17.6°C to 19.1°C and overnight lows from 7.8°C to 9.8°C over the same span.
September is one of the warmer months of the year in Snohomish and one of the drier months, so plan for around 19°C daytime highs and 9.3°C at night.
Not quite — September is the 10th coolest month in Snohomish, averaging 14.2°C.
For September in Snohomish, pack light layers you can adjust through the day, with typical highs of 19°C and lows of 9.3°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 79% — quite humid.
Average wind speed in September is 0.3 m/s. The windiest September on record averaged 0.4 m/s (1990).
The wettest September on record was 2013 with 224 mm. On average, September sees 83 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 Snohomish 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.
