September weather in Lake Forest, IL
The average temperature in Lake Forest in September is 64.9°F (54.7°F–75.2°F). Average precipitation: 3.56 inches.
September is a fall month in Lake Forest, and is warmer than the annual average of 49.6°F. Daily temperatures swing about 20.5°F between overnight low and afternoon high. Expect about 10 days with precipitation. Daylight averages about 12h 16m. For travel, September is one of the best months of the year to visit.
Avg High
75.2°F
Avg Low
54.7°F
Precipitation
3.56 in
Daylight
12h 16m
September records in Lake Forest
| Date | Record High | Record Low | Record Precip |
|---|---|---|---|
| September 1 | 95.0°F (2012) | 44.1°F (2009) | 2.01 in (1989) |
| September 2 | 96.1°F (2011) | 46.9°F (2001) | 0.74 in (2018) |
| September 3 | 91.9°F (2008) | 48.0°F (1994) | 1.92 in (2010) |
| September 4 | 91.0°F (1985) | 46.0°F (1982) | 1.09 in (1991) |
| September 5 | 93.0°F (1990) | 46.9°F (1997) | 3.20 in (2008) |
| September 6 | 91.9°F (2007) | 42.1°F (1988) | 1.95 in (1983) |
| September 7 | 97.0°F (1990) | 45.0°F (1988) | 0.81 in (2001) |
| September 8 | 95.0°F (1985) | 48.0°F (1982) | 1.08 in (1995) |
| September 9 | 91.0°F (1985) | 46.9°F (2008) | 1.03 in (2008) |
| September 10 | 93.9°F (1991) | 45.0°F (2008) | 0.86 in (1992) |
| September 11 | 95.0°F (2013) | 39.9°F (1993) | 1.08 in (2015) |
| September 12 | 91.9°F (2005) | 45.0°F (2007) | 2.56 in (2000) |
| September 13 | 91.0°F (1998) | 39.9°F (2014) | 3.20 in (2008) |
| September 14 | 93.9°F (1998) | 41.0°F (2014) | 3.35 in (2008) |
| September 15 | 90.0°F (1994) | 39.0°F (2007) | 1.07 in (2008) |
| September 16 | 91.0°F (1994) | 37.9°F (1984) | 0.81 in (2013) |
| September 17 | 88.0°F (2017) | 39.0°F (1984) | 1.12 in (1997) |
| September 18 | 90.0°F (1988) | 45.0°F (1995) | 1.69 in (2015) |
| September 19 | 88.0°F (1985) | 37.9°F (2012) | 2.28 in (2001) |
| September 20 | 88.0°F (1997) | 37.0°F (1991) | 0.74 in (1997) |
| September 21 | 90.0°F (2017) | 37.0°F (1991) | 0.90 in (2001) |
| September 22 | 91.9°F (2017) | 30.9°F (1995) | 0.42 in (1995) |
| September 23 | 93.9°F (2017) | 30.0°F (1995) | 2.02 in (2000) |
| September 24 | 93.0°F (2017) | 34.0°F (1989) | 0.98 in (2006) |
| September 25 | 91.9°F (2007) | 37.9°F (1985) | 2.25 in (1986) |
| September 26 | 91.9°F (2017) | 37.0°F (1984) | 1.26 in (2011) |
| September 27 | 91.9°F (1998) | 33.1°F (1991) | 2.11 in (1996) |
| September 28 | 84.9°F (1990) | 35.1°F (1991) | 1.20 in (1999) |
| September 29 | 82.0°F (2013) | 35.1°F (1984) | 1.20 in (1986) |
| September 30 | 84.0°F (2002) | 30.0°F (1993) | 1.61 in (1986) |