McHenry County Weather in September
Average highs run from 79°F on September 1 to 70°F on September 30, and lows from 57°F to 48°F. Normal precipitation for the month is 3.54 in over about 8 wet days.
September day by day
The normal high and low for each date, and the record, in °F.
- Normal low
- Normal high
- Record high
- Record low
September at a glance
- Average high
- 74°F
- Average low
- 52°F
- Precipitation
- 3.54 in
- Record high
- 101°FSep 3, 1953
- Record low
- 23°FSep 23, 1974
- Chance of a freeze
- 4%
- Days of 90°F or more
- 2.5
- Daylight
- 13 h 09 min to 11 h 47 min
- Cloud cover
- 51%
- Humidity
- 75%
- Dew point
- 54°F
- Wind
- 9.2 mph
Every day of the month
A wet day has at least 0.01 inch of precipitation; snow means at least 0.1 inch of snowfall.
| Date | Normal high | Normal low | Record high | Record low | Chance wet | Chance of snow |
|---|---|---|---|---|---|---|
| Sep 1 | 79°F | 57°F | 100°F 1953 | 40°F 1967 | 26% | 0% |
| Sep 2 | 78°F | 56°F | 99°F 1953 | 39°F 1967 | 26% | 0% |
| Sep 3 | 78°F | 56°F | 101°F 1953 | 41°F 2009 | 26% | 0% |
| Sep 4 | 78°F | 56°F | 94°F 1953 | 37°F 1974 | 26% | 0% |
| Sep 5 | 78°F | 55°F | 90°F 1990 | 40°F 1974 | 26% | 0% |
| Sep 6 | 77°F | 55°F | 92°F 1999 | 36°F 1962 | 26% | 0% |
| Sep 7 | 77°F | 55°F | 100°F 1985 | 36°F 1956 | 26% | 0% |
| Sep 8 | 77°F | 55°F | 95°F 1960 | 38°F 1986 | 26% | 0% |
| Sep 9 | 77°F | 54°F | 96°F 1978 | 34°F 1975 | 27% | 0% |
| Sep 10 | 76°F | 54°F | 95°F 1955 | 40°F 2008 | 27% | 0% |
| Sep 11 | 76°F | 54°F | 93°F 1961 | 28°F 1995 | 27% | 0% |
| Sep 12 | 76°F | 53°F | 91°F 1952 | 33°F 1955 | 27% | 0% |
| Sep 13 | 75°F | 53°F | 90°F 1952 | 34°F 1953 | 27% | 0% |
| Sep 14 | 75°F | 53°F | 91°F 2005 | 35°F 1963 | 27% | 0% |
| Sep 15 | 75°F | 53°F | 90°F 1971 | 33°F 2007 | 27% | 0% |
| Sep 16 | 75°F | 52°F | 89°F 1994 | 33°F 2007 | 27% | 0% |
| Sep 17 | 74°F | 52°F | 91°F 1955 | 37°F 1984 | 27% | 0% |
| Sep 18 | 74°F | 52°F | 92°F 1955 | 33°F 1959 | 27% | 0% |
| Sep 19 | 74°F | 51°F | 91°F 1955 | 33°F 2012 | 27% | 0% |
| Sep 20 | 73°F | 51°F | 89°F 1978 | 28°F 1956 | 27% | 0% |
| Sep 21 | 73°F | 51°F | 88°F 1959 | 28°F 1991 | 28% | 0% |
| Sep 22 | 73°F | 51°F | 90°F 2017 | 32°F 1953 | 28% | 0% |
| Sep 23 | 72°F | 50°F | 92°F 2017 | 23°F 1974 | 28% | 0% |
| Sep 24 | 72°F | 50°F | 91°F 2017 | 28°F 1974 | 28% | 0% |
| Sep 25 | 71°F | 50°F | 88°F 2007 | 34°F 1985 | 28% | 0% |
| Sep 26 | 71°F | 50°F | 89°F 2017 | 34°F 1984 | 28% | 0% |
| Sep 27 | 71°F | 49°F | 88°F 1998 | 26°F 1991 | 28% | 0% |
| Sep 28 | 70°F | 49°F | 86°F 1954 | 27°F 1991 | 29% | 0% |
| Sep 29 | 70°F | 49°F | 89°F 1952 | 30°F 1991 | 29% | 0% |
| Sep 30 | 70°F | 48°F | 90°F 1953 | 28°F 1993 | 29% | 0% |
Chance of rain
- Chance of a wet day
- Chance of snowfall
Sunrise and sunset
Times for 2026, local time (CDT).
- September 1
- sunrise 6:19 AM, sunset 7:28 PM
- September 30
- sunrise 6:50 AM, sunset 6:37 PM
Other months
Sources
Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USC00112048 (Crystal Lake 4NW), public domain. Records: NOAA GHCN-Daily, station USC00471205, every year on file, quality-flagged values removed. Cloud, humidity, wind and sunshine: NASA POWER (MERRA-2, CERES and GEWEX SRB), 1991-2020. The data was obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division: POWER Daily API v2, accessed 2026-09-24. Sun and moon: computed with the NOAA solar equations and Meeus.