September 24: ORD

Today is September 24th. It's the 267th day of the year. 98 days remain. It's week 39 of the year.

Unless noted, the following data is based upon observations collected by the National Weather Service, Chicago, at O'Hare International Airport (ORD) between November 1978 and last year. ORD has been the official site of record for Chicago since Thursday, January 17, 1980.

According to the National Climatic Data Center (NCDC), the normal high is 72 and the normal low is 51. I've calculated the 32-year averages at 69 and 49.

On the warm side, in 2007 the high was 90 with a low of 68. In 1984 the high was 84 with a low of 61. The other warm lows were 64 two years ago (in 2009), 64 in 1986 and 63 in 2005. The record high of 91 was set way back in 1891. The record warmest low of 71 occurred in 1930. These records occurred at a time when the official readings were taken adjacent to Lake Michigan. 16 of the past 32 highs (50%) were in the 60s. 13 highs (41%) were in the warm: 70s (8), 80s (4) and 90s (1). Three highs (9%) were in the cool 50s.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1978 the high was 79 with a low of 49, a 30 degree spread. In 1976 the high was 69 with a cold low of 34, a 35 degree spread. That low of 34 was colder than the record low. In 1966 the high was 72 with a cold low of 39, a 33 degree spread. In 1965 the high was a cool 54 with a low of 42, a cool day. In 1960 the high was 84 with a low of 63, a warm day.

More recently, there were large spreads of 31 degrees in 1993 (69/38) and 30 degrees in 1983 (66/36). There was a small spread of seven degrees in 2000 (56/49).

On the cool side, in both 1985 and 1989, highs were 61 with co-record lows of 35. The record low of 35 originally occurred in 1942. In 1991 the high was 57 with a low of 40. In 1995 the high was 62 with a low of 37, our most recent 30s low. The other cool lows were 36 in 1983 and 38 in 1993. The other cool highs were 55 in 2001 (our most recent 50s high) and 56 in 2000. The record coolest high of 51 occurred in 1942. 15 of the last 32 lows (47%) were in the 40s. Five lows (15%) were in the cold 30s. 12 lows (38%) were in the warm: 50s (7) and 60s (5).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:15 and sunrise is at 6:43. Sunset is at 18:47 and twilight ends at 19:15. There's a total of 12 hours, 4 minutes of daylight today and 13 hours between twilights. We lost four minutes of daylight from yesterday. Tomorrow twilight begins at 6:16 and sunrise is at 6:44. The moon is waning crescent. Illumination was 15% at midnight, will be 11% at noon and 7% at midnight tonight. Moonrise is at 3:16 this morning. Moonset is at 16:56 this afternoon. Moonrise is at 4:29 tomorrow morning. Moonlight time is 13 hours, 40 minutes which is 39 minutes shorter than yesterday.

Warm Fall began September 22 and runs for 41 days through November 1. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the 30s and 40s occur infrequently. Columbus Day is in 16 days.