September 23: ORD

Today is September 23rd. It's the 266th day of the year. 99 days remain. It's week 38 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 70 and 49.

On the hot side, in 2010 (last year) the high was 89 with a low of 65. Two years prior, in 2008, the high was 82 with a low of 59. The other warm highs were 85 in 2004 and 84 in 2007. The record high of 91 was set in 1937. Our warmest low was 64 in 1986. The record warmest low of 71 occurred way back in 1891, a time when the official readings were taken adjacent to Lake Michigan. 22 of the past 32 highs (69%) were in the: 60s (13) and 70s (9). Five highs were in the warm 80s and five were in the cool 50s. The five 80s highs occurred more recently, from 1999 through last year (2010). The five 50s highs occurred longer ago, from 1983 through 1995.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1976 the high was 68 with a cold low of 36, a 32 degree spread. In 1975 the high was 72 with a low of 42, a 30 degree spread. In 1974 the high was 60 with a cold low of 28, a 32 degree spread and cool day. That low of 28 was colder than the record low. In 1972 the high was a cool 60 degrees. In 1968 the low was a warm 63 degrees. In 1966 the high was 73 with a low of 42, a 31 degree spread. In 1960 the high was 67 with a low of 61, a six degree spread.

More recently, there were large spreads of 34 degrees in 2007 (84/50), 31 degrees in 2004 (85/54), 30 degrees in 2002 (69/39) and 30 degrees in 1979 (73/43). There was a small spread of five degrees in 2005 (67/62).

On the cool side, in 1995 the high was 58 with the record low of 29. In 1989 the high was 54 with a low of 37. In 1983 the high was 56 with a low of 35. In 1981 the high was 63 with a low of 35. In 1992 the high was 59 with a low of 40. The other cold low was 39 in 2002. The other cool high was 59 in 1990. The record coolest high of 51 occurred back in 1928, a time when the official readings were taken adjacent to Lake Michigan. 23 of the last 32 lows (72%) were in the: 40s (13) and 50s (10). The last 40s low was 48 in 2003. Five lows were in the cold: 20s (1) and 30s (4). The last 30s low was 39 in 2002. Four lows were in the warm 60s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:13 and sunrise is at 6:41. Sunset is at 18:49 and twilight ends at 19:17. There's a total of 12 hours, 8 minutes of daylight today and 13 hours, 4 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:15 and sunrise is at 6:43. The moon is waning crescent. Illumination was 23% at midnight, will be 19% at noon and 15% at midnight tonight. Moonrise is at 2:04 this morning. Moonset is at 16:23 this afternoon. Moonrise is at 3:16 tomorrow morning. Moonlight time is 14 hours, 19 minutes which is 33 minutes shorter than yesterday.

Warm Fall began September 22 (yesterday) 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 17 days.