September is one of the warmer months of the year in Mchenry, with average highs near 23.4°C and lows around 12.4°C (mean 17.9°C). It is about average for rainfall, averaging 87 mm of rainfall and 73% relative humidity across the period.
September is one of the warmer months of the year in Mchenry. Across 45 years of records, the warmest September in Mchenry was 2005 — when the month averaged 21.1°C — while the coldest was 1993 at 13.9°C. Typical September days reach 23.4°C with nights near 12.4°C. The long-term trend is warming, about 0.5°C per decade.
September is about average for rainfall in Mchenry, averaging 87 mm of rainfall. The wettest September on record was 1986 with 242 mm, while the driest was 2017 at 9 mm.
Relative humidity in Mchenry during September averages 73%. The most humid September was 2019 at 85%, and the least humid was 1999 at 64%.
September receives about 4.3 kWh/m²/day of solar energy in Mchenry. The sunniest September was 2004 at 5.2 kWh/m²/day, and the cloudiest was 1986 at 3.2.
Average wind speed in Mchenry during September is 2.9 m/s. The windiest Septembers were 1985 and 2000 at 3.4 m/s, while the calmest were 2009 and 2025 at 2.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 17.1°C | 17.2°C | 18.2°C | 18.3°C | 19.0°C | +1.9°C |
| Avg High | 22.8°C | 22.9°C | 23.8°C | 23.4°C | 24.7°C | +1.9°C |
| Avg Low | 11.5°C | 11.5°C | 12.6°C | 13.1°C | 13.5°C | +2°C |
| Avg Rain | 90 mm | 76 mm | 91 mm | 100 mm | 77 mm | -12 mm |
September temperatures in Mchenry have risen by about 2.4°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -0.4°C (1984) to a record high of 34.7°C (2023).
Rainfall in September is about average for rainfall, averaging 87 mm, with a wettest year of 242 mm.
One of the best times to visit Mchenry
September is one of the best times to visit Mchenry. Expect days averaging 23.4°C and nights around 12.4°C (mean 17.9°C) — warmer than Mchenry's yearly average — with higher rainfall (87 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 | 25.3°C | 19.5°C | 13.7°C | 30.3°C | 6.4°C | 49 mm | 70% | 2.2 m/s | 4.8 |
| 2024 | 26.7°C | 20.3°C | 14.0°C | 32.1°C | 7.1°C | 46 mm | 64% | 2.5 m/s | 4.9 |
| 2023 | 24.7°C | 19.6°C | 14.5°C | 34.7°C | 10.1°C | 103 mm | 74% | 2.5 m/s | 3.9 |
| 2022 | 23.3°C | 18.0°C | 12.8°C | 30.1°C | 4.3°C | 125 mm | 77% | 2.7 m/s | 4.4 |
| 2021 | 26.2°C | 20.0°C | 13.9°C | 31.4°C | 7.9°C | 28 mm | 68% | 3 m/s | 4.6 |
| 2020 | 21.7°C | 16.7°C | 11.8°C | 28.4°C | 7.3°C | 116 mm | 79% | 3.3 m/s | 3.7 |
| 2019 | 23.7°C | 19.4°C | 15.0°C | 27.7°C | 10.5°C | 230 mm | 85% | 2.9 m/s | 3.6 |
| 2018 | 23.0°C | 18.4°C | 13.8°C | 29.8°C | 2.2°C | 184 mm | 83% | 2.6 m/s | 4.1 |
| 2017 | 25.3°C | 19.4°C | 13.4°C | 33.7°C | 8.1°C | 9 mm | 70% | 2.5 m/s | 4.9 |
| 2016 | 24.4°C | 19.8°C | 15.2°C | 31.9°C | 8.1°C | 92 mm | 80% | 3.1 m/s | 4.2 |
| 2015 | 25.0°C | 19.9°C | 14.8°C | 33.0°C | 7.8°C | 122 mm | 77% | 2.8 m/s | 4.5 |
| 2014 | 22.3°C | 16.6°C | 10.9°C | 27.5°C | 4.1°C | 72 mm | 78% | 2.6 m/s | 4.4 |
| 2013 | 24.0°C | 18.4°C | 12.9°C | 33.9°C | 7.0°C | 59 mm | 76% | 2.8 m/s | 4.7 |
| 2012 | 23.3°C | 17.3°C | 11.3°C | 31.8°C | 2.7°C | 53 mm | 67% | 3 m/s | 4.7 |
| 2011 | 21.3°C | 16.5°C | 11.8°C | 33.9°C | 3.6°C | 107 mm | 74% | 3.1 m/s | 4.1 |
| 2010 | 22.0°C | 17.0°C | 12.0°C | 29.5°C | 5.7°C | 68 mm | 77% | 3.3 m/s | 4.2 |
| 2009 | 23.3°C | 18.1°C | 13.0°C | 28.8°C | 3.8°C | 37 mm | 77% | 2.2 m/s | 4.5 |
| 2008 | 22.7°C | 17.9°C | 13.2°C | 33.3°C | 7.4°C | 168 mm | 81% | 2.6 m/s | 3.9 |
| 2007 | 23.6°C | 17.9°C | 12.2°C | 30.0°C | 2.1°C | 46 mm | 78% | 3.1 m/s | 4.9 |
| 2006 | 21.3°C | 16.3°C | 11.4°C | 28.2°C | 4.4°C | 101 mm | 77% | 3 m/s | 3.7 |
| 2005 🔥 | 27.3°C | 21.1°C | 14.9°C | 33.5°C | 4.5°C | 84 mm | 66% | 3.1 m/s | 4.4 |
| 2004 | 26.1°C | 19.7°C | 13.4°C | 30.6°C | 6.8°C | 13 mm | 68% | 2.8 m/s | 5.2 |
| 2003 | 23.9°C | 17.9°C | 11.9°C | 32.7°C | 3.0°C | 49 mm | 66% | 3.2 m/s | 4.5 |
| 2002 | 25.6°C | 19.4°C | 13.2°C | 32.2°C | 4.6°C | 92 mm | 71% | 2.5 m/s | 4.7 |
| 2001 | 21.6°C | 16.3°C | 11.0°C | 31.1°C | 2.3°C | 172 mm | 78% | 3 m/s | 4.3 |
| 2000 | 23.0°C | 17.5°C | 11.9°C | 34.5°C | 4.0°C | 144 mm | 72% | 3.4 m/s | 4.1 |
| 1999 | 24.2°C | 17.6°C | 11.0°C | 33.3°C | 4.4°C | 102 mm | 64% | 3.1 m/s | 4.7 |
| 1998 | 26.1°C | 19.9°C | 13.7°C | 33.2°C | 9.8°C | 66 mm | 69% | 2.6 m/s | 4.6 |
| 1997 | 23.6°C | 17.8°C | 11.9°C | 30.4°C | 6.9°C | 70 mm | 72% | 3 m/s | 4.2 |
| 1996 | 23.0°C | 17.4°C | 11.9°C | 30.1°C | 6.2°C | 53 mm | 72% | 2.7 m/s | 4.2 |
| 1995 | 22.0°C | 16.2°C | 10.3°C | 30.5°C | 1.1°C | 42 mm | 67% | 3 m/s | 4.3 |
| 1994 | 23.8°C | 18.4°C | 12.9°C | 31.2°C | 6.7°C | 49 mm | 74% | 2.6 m/s | 4 |
| 1993 ❄️ | 18.5°C | 13.9°C | 9.2°C | 24.4°C | 0.3°C | 109 mm | 81% | 3 m/s | 3.3 |
| 1992 | 21.3°C | 15.9°C | 10.4°C | 27.4°C | 0.7°C | 135 mm | 77% | 3.1 m/s | 3.8 |
| 1991 | 22.4°C | 16.8°C | 11.1°C | 32.3°C | 0.3°C | 94 mm | 68% | 3 m/s | 4.3 |
| 1990 | 23.9°C | 18.2°C | 12.5°C | 33.1°C | 4.2°C | 39 mm | 73% | 3 m/s | 4.3 |
| 1989 | 21.1°C | 15.8°C | 10.4°C | 27.5°C | 2.4°C | 56 mm | 75% | 2.6 m/s | 4.4 |
| 1988 | 25.3°C | 18.7°C | 12.0°C | 31.2°C | 6.2°C | 81 mm | 64% | 3.2 m/s | 4.1 |
| 1987 | 21.5°C | 16.7°C | 11.9°C | 26.5°C | 6.5°C | 63 mm | 80% | 2.5 m/s | 3.9 |
| 1986 🌧️ | 22.7°C | 17.8°C | 12.9°C | 27.4°C | 5.5°C | 242 mm | 78% | 2.9 m/s | 3.2 |
| 1985 | 23.2°C | 17.9°C | 12.7°C | 33.4°C | 3.5°C | 76 mm | 72% | 3.4 m/s | 3.6 |
| 1984 | 23.0°C | 16.6°C | 10.3°C | 31.3°C | -0.4°C | 79 mm | 67% | 3.2 m/s | 4 |
| 1983 | 24.0°C | 17.7°C | 11.4°C | 32.6°C | 2.5°C | 87 mm | 68% | 3.1 m/s | — |
| 1982 | 22.9°C | 17.1°C | 11.2°C | 29.2°C | 3.6°C | 34 mm | 74% | 3 m/s | — |
| 1981 | 21.2°C | 16.0°C | 10.7°C | 27.4°C | 2.7°C | 87 mm | 76% | 3 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 23.4°C with lows near 12.4°C (mean 17.9°C), based on 45 years of NASA POWER data.
September averages 87 mm of rainfall in Mchenry, about average for rainfall. The wettest on record was 242 mm in 1986.
The hottest September reached 34.7°C in 2023. The coldest dipped to -0.4°C in 1984.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2.4°C. Daytime highs moved from 22.9°C to 25.2°C and overnight lows from 11.3°C to 13.8°C over the same span.
September is one of the warmer months of the year in Mchenry and about average for rainfall, so plan for around 23.4°C daytime highs and 12.4°C at night.
Not quite — September is the 9th coolest month in Mchenry, averaging 17.9°C.
For September in Mchenry, pack light layers you can adjust through the day, with typical highs of 23.4°C and lows of 12.4°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 73% — moderately humid.
Average wind speed in September is 2.9 m/s. The windiest September on record averaged 3.4 m/s (1985).
The wettest September on record was 1986 with 242 mm. On average, September sees 87 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 Mchenry 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.
