September is one of the warmer months of the year in Castle Rock, with average highs near 24.6°C and lows around 8.6°C (mean 16.6°C). It is about average for rainfall, averaging 35 mm of rainfall and 45% relative humidity across the period.
September is one of the warmer months of the year in Castle Rock. Across 45 years of records, the warmest September in Castle Rock was 2019 — when the month averaged 19.3°C — while the coldest was 2006 at 13.2°C. Typical September days reach 24.6°C with nights near 8.6°C. The long-term trend is warming, about 0.7°C per decade.
September is about average for rainfall in Castle Rock, averaging 35 mm of rainfall. The wettest September on record was 2013 with 148 mm, while the driest were 1992 and 2010 at 5 mm.
Relative humidity in Castle Rock during September averages 45%. The most humid September was 2013 at 58%, and the least humid was 2010 at 34%.
September receives about 5.3 kWh/m²/day of solar energy in Castle Rock. The sunniest September was 2010 at 6 kWh/m²/day, and the cloudiest was 1995 at 4.7.
Average wind speed in Castle Rock during September is 2.2 m/s. The windiest September was 1985 at 2.6 m/s, while the calmest were 2012, 2015 and 2025, among others at 2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 15.5°C | 16.0°C | 16.2°C | 17.6°C | 18.0°C | +2.5°C |
| Avg High | 23.5°C | 24.0°C | 24.3°C | 25.6°C | 26.3°C | +2.8°C |
| Avg Low | 7.6°C | 8.1°C | 8.2°C | 9.6°C | 9.9°C | +2.3°C |
| Avg Rain | 31 mm | 37 mm | 32 mm | 41 mm | 31 mm | -1 mm |
September temperatures in Castle Rock have risen by about 2.7°C between 1981–1985 and 2021–2025.
September has ranged from a record low of -9.3°C (1985) to a record high of 34.3°C (2019).
Rainfall in September is about average for rainfall, averaging 35 mm, with a wettest year of 148 mm.
One of the best times to visit Castle Rock
September is one of the best times to visit Castle Rock. Expect days averaging 24.6°C and nights around 8.6°C (mean 16.6°C) — warmer than Castle Rock's yearly average — with moderate rainfall (35 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 | 24.8°C | 17.1°C | 9.4°C | 31.0°C | 5.7°C | 50 mm | 47% | 2 m/s | 5.1 |
| 2024 | 27.4°C | 19.1°C | 10.8°C | 31.1°C | 4.6°C | 23 mm | 37% | 2.5 m/s | 5.6 |
| 2023 | 25.9°C | 17.6°C | 9.4°C | 34.0°C | 4.2°C | 38 mm | 42% | 2.1 m/s | 5.7 |
| 2022 | 27.4°C | 19.1°C | 10.9°C | 34.2°C | 4.9°C | 25 mm | 40% | 2.1 m/s | 5.3 |
| 2021 | 27.0°C | 18.7°C | 10.4°C | 33.8°C | 2.7°C | 25 mm | 39% | 2.1 m/s | 5.7 |
| 2020 | 25.0°C | 16.6°C | 8.2°C | 34.2°C | -3.9°C | 22 mm | 38% | 2.2 m/s | 5.2 |
| 2019 🔥 | 27.7°C | 19.3°C | 10.9°C | 34.3°C | 4.2°C | 24 mm | 40% | 2.5 m/s | 5.8 |
| 2018 | 26.7°C | 18.5°C | 10.3°C | 32.1°C | 3.3°C | 20 mm | 38% | 2.1 m/s | 5.5 |
| 2017 | 24.2°C | 16.5°C | 8.8°C | 32.6°C | 0.1°C | 46 mm | 50% | 2.2 m/s | 4.8 |
| 2016 | 26.0°C | 17.5°C | 9.0°C | 30.1°C | 3.2°C | 8 mm | 41% | 2.2 m/s | 5.6 |
| 2015 | 26.9°C | 18.8°C | 10.8°C | 30.1°C | 6.7°C | 7 mm | 42% | 2 m/s | 5.6 |
| 2014 | 24.8°C | 17.0°C | 9.2°C | 31.9°C | -2.3°C | 55 mm | 52% | 2.1 m/s | 5.4 |
| 2013 🌧️ | 24.2°C | 17.0°C | 9.9°C | 32.4°C | -0.2°C | 148 mm | 58% | 2.3 m/s | 5 |
| 2012 | 24.4°C | 16.8°C | 9.2°C | 31.9°C | 5.3°C | 50 mm | 43% | 2 m/s | 5.2 |
| 2011 | 24.0°C | 16.4°C | 8.7°C | 32.6°C | 3.8°C | 42 mm | 47% | 2.2 m/s | 5.3 |
| 2010 | 27.5°C | 18.6°C | 9.6°C | 32.3°C | 6.0°C | 5 mm | 34% | 2.3 m/s | 6 |
| 2009 | 22.7°C | 15.4°C | 8.1°C | 30.4°C | 0.0°C | 44 mm | 51% | 2.5 m/s | 5 |
| 2008 | 24.3°C | 16.1°C | 7.8°C | 30.2°C | 3.5°C | 36 mm | 46% | 2.1 m/s | 5.5 |
| 2007 | 25.5°C | 17.4°C | 9.4°C | 30.1°C | 0.9°C | 21 mm | 44% | 2.5 m/s | 5.5 |
| 2006 ❄️ | 21.1°C | 13.2°C | 5.3°C | 28.0°C | -1.3°C | 38 mm | 48% | 2.3 m/s | 5.2 |
| 2005 | 26.2°C | 18.0°C | 9.8°C | 30.2°C | 4.9°C | 17 mm | 39% | 2.2 m/s | 5.3 |
| 2004 | 23.9°C | 16.1°C | 8.4°C | 29.9°C | 0.9°C | 36 mm | 47% | 2.4 m/s | 5.4 |
| 2003 | 23.1°C | 14.8°C | 6.5°C | 28.7°C | -1.4°C | 19 mm | 45% | 2.3 m/s | 5.5 |
| 2002 | 24.6°C | 16.7°C | 8.8°C | 32.8°C | 2.3°C | 49 mm | 43% | 2.3 m/s | 5.3 |
| 2001 | 25.7°C | 17.6°C | 9.4°C | 30.3°C | -0.8°C | 28 mm | 41% | 2.2 m/s | 5.6 |
| 2000 | 25.7°C | 16.9°C | 8.2°C | 32.0°C | -3.8°C | 35 mm | 41% | 2.4 m/s | 5.2 |
| 1999 | 22.3°C | 14.1°C | 6.0°C | 29.5°C | -4.8°C | 27 mm | 48% | 2.1 m/s | 5.3 |
| 1998 | 26.7°C | 18.6°C | 10.5°C | 31.5°C | 4.7°C | 23 mm | 44% | 2.2 m/s | 5.7 |
| 1997 | 24.8°C | 17.2°C | 9.5°C | 28.7°C | 2.4°C | 38 mm | 54% | 2 m/s | 5.3 |
| 1996 | 22.1°C | 14.5°C | 6.9°C | 30.7°C | -5.0°C | 74 mm | 50% | 2.2 m/s | 5 |
| 1995 | 22.5°C | 15.0°C | 7.5°C | 33.6°C | -5.7°C | 59 mm | 51% | 2 m/s | 4.7 |
| 1994 | 24.7°C | 16.7°C | 8.7°C | 30.0°C | -3.0°C | 24 mm | 41% | 2.1 m/s | 5.2 |
| 1993 | 22.9°C | 14.2°C | 5.6°C | 29.2°C | -4.2°C | 48 mm | 47% | 2.2 m/s | 4.9 |
| 1992 | 25.0°C | 16.6°C | 8.2°C | 29.9°C | 1.5°C | 5 mm | 40% | 2.2 m/s | 5.6 |
| 1991 | 23.2°C | 15.6°C | 8.1°C | 27.4°C | 2.4°C | 22 mm | 49% | 2.3 m/s | 5.4 |
| 1990 | 25.3°C | 17.6°C | 9.9°C | 32.4°C | 4.9°C | 48 mm | 49% | 2.2 m/s | 5.3 |
| 1989 | 24.3°C | 15.9°C | 7.5°C | 31.4°C | -0.1°C | 43 mm | 45% | 2.5 m/s | 5.2 |
| 1988 | 23.6°C | 15.2°C | 6.8°C | 31.6°C | 0.4°C | 29 mm | 40% | 2.5 m/s | 5.2 |
| 1987 | 23.2°C | 15.4°C | 7.7°C | 29.1°C | 3.0°C | 18 mm | 46% | 2.1 m/s | 5.4 |
| 1986 | 23.0°C | 15.0°C | 6.9°C | 27.5°C | 0.4°C | 21 mm | 47% | 2.4 m/s | 5 |
| 1985 | 21.5°C | 13.6°C | 5.6°C | 29.0°C | -9.3°C | 59 mm | 50% | 2.6 m/s | 4.9 |
| 1984 | 23.4°C | 15.3°C | 7.2°C | 30.1°C | -4.8°C | 19 mm | 48% | 2.4 m/s | 5 |
| 1983 | 25.5°C | 17.0°C | 8.6°C | 31.4°C | -5.0°C | 10 mm | 44% | 2.4 m/s | — |
| 1982 | 22.3°C | 15.1°C | 8.0°C | 30.9°C | 1.8°C | 60 mm | 55% | 2.2 m/s | — |
| 1981 | 24.6°C | 17.1°C | 9.7°C | 30.2°C | 5.7°C | 22 mm | 46% | 2.2 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 24.6°C with lows near 8.6°C (mean 16.6°C), based on 45 years of NASA POWER data.
September averages 35 mm of rainfall in Castle Rock, about average for rainfall. The wettest on record was 148 mm in 2013.
The hottest September reached 34.3°C in 2019. The coldest dipped to -9.3°C in 1985.
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 23.5°C to 26.5°C and overnight lows from 7.8°C to 10.2°C over the same span.
September is one of the warmer months of the year in Castle Rock and about average for rainfall, so plan for around 24.6°C daytime highs and 8.6°C at night.
Not quite — September is the 9th coolest month in Castle Rock, averaging 16.6°C.
For September in Castle Rock, pack light layers you can adjust through the day, with typical highs of 24.6°C and lows of 8.6°C.
Relative humidity in September averages 45% — relatively dry.
Average wind speed in September is 2.2 m/s. The windiest September on record averaged 2.6 m/s (1985).
The wettest September on record was 2013 with 148 mm. On average, September sees 35 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 Castle Rock 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.
