September 20: ORD

Today is September 20th. It's the 263rd day of the year. 102 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 73 and the normal low is 52. I've calculated the 32-year averages at 72 and 52.

On the hot side, in 1980 the high was 90 (our only 90s high) with a low of 67. In 1998 the high was 86 with a low of 65. The other hot high was 85 in 1994. The record high of 91 and record warmest low of 73 were set on the same hot day back in 1931, a time when the official readings were taken adjacent to Lake Michigan. That record high of 91 was first set way back in 1895. 25 of the past 32 highs (78%) were in the: 60s (12) and 70s (13). Six highs were in the warm: 80s (5) and 90s (1). One high was in the cool 50s. For eight consecutive years, from 1986 through 1993, highs were in the 60s & 70s. Likewise, the same occurred for six years from 1999-2004.

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 a hot 89 with a low of 62, a hot day. In 1975 the high was a cool 60 degrees. In 1974 the high was a cool 61 with a low of 55, a six degree spread. In 1970 the high was a hot 85 degrees. In 1967 the high was 85 with a low of 66, a hot day. In 1965 the high was 84 with a warm low of 69, a hot day. In 1962 the high was 60 with a low of 35, a cool day. That low of 35 was colder than the record low of 36. In 1960 the high was 65 with a low of 58, a seven degree spread. In 1959 the high was 88 with a low of 64, a hot day.

More recently, there were large spreads of 34 degrees in 1983 (78/44), 31 degrees in 1979 (79/48) and 30 degrees in 2003 (71/41). There were no small spreads of up to seven degrees.

On the cool side, in 1991 the high was 60 with the record low of 36 (our only 30s low). In 1982 the high was 55 (our only 50s high) with a low of 43. Five years ago, in 2006, the high was 62 with a low of 42. The other cool high is 60 in 1995. The record coolest high of 52 occurred way back in 1901, a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 32 lows (81%) were in the: 40s (9) and 50s (17). One low was in the cold 30s and five were in the warm 60s. For ten consecutive years, from 1981 through 1990, lows were in the 40s & 50s. Likewise, the same occurred for six years from 1992-1997.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:10 and sunrise is at 6:38. Sunset is at 18:55 and twilight ends at 19:23. There's a total of 12 hours, 17 minutes of daylight today and 13 hours, 13 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:11 and sunrise is at 6:39. The moon reaches last quarter today at 8:39. Illumination was 53% at midnight, will be 48% at noon and 43% at midnight tonight. Moonset is at 14:24 this afternoon. Moonrise is at 23:53 tonight. Moonset is at 15:08 tomorrow afternoon. Moonlight time is 14 hours, 31 minutes which is 9 minutes shorter than yesterday.

Summer began June 4 and runs for 110 days through September 21. High temperatures in this period are usually in the 70s and 80s. Highs in the 60s, 90s and 100s occur infrequently. Columbus Day is in 20 days.