September 30: ORD

Today is September 30th. It's the 273rd day of the year. 92 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 69 and the normal low is 48. I've calculated the 32-year averages at 72 and 48.

On the warm side, in 2002 the high was 85 with the near-record warmest low of 68. The record warmest low of 69 degrees occurred in 1971. In 1995 the high was 84 with a low of 65. In 1982 the high was 85 with a low of 58. In 2007 the high was 83 with a low of 59. Other warm highs were 83 in both 1981 and 1994. Additionally, it was 82 in 1991 and 81 in 1983. The record high of 92 was set in 1971. 22 of the past 32 highs (69%) were in the: 60s (10) and 70s (12). There were two long stretches of highs in the 60s & 70s. The first was seven years from 1984 through 1990. The second was six years from 1996 through 2001. Eight highs were in the warm 80s and two were in the cool 50s. The two 50s highs were preceded by highs in the 80s: 85 in 2002 followed by 56 in 2003 and 83 in 2007 followed by 59 in 2008.

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 77 with a low of 47, a 30 degree spread. In 1973 the high was 65 with a warm low of 60, a five degree spread. In 1972 the high was 53 with a low of 36, a cool day. In 1971 the high was 92 with a low of 65, a hot day. 1971 was the year of the record high of 92 and record warmest low of 69, both set at Midway. In 1968 the high was 80 with a low of 50, a 30 degree spread. In 1964 the low was a cold 36 degrees. In 1963 the high was 77 with a low of 45, a 32 degree spread. In 1962 the high was 70 with a cold low of 36, a 34 degree spread. In 1961 the high was 75 with a low of 44, a 31 degree spread. In 1960 the high was a cool 57 degrees.

More recently, there were large spreads of 36 degrees in 2004 (72/36), 34 degrees in 1989 (77/43), 33 degrees in 1983 (81/48), 31 degrees in 1994 (83/52), 31 degrees in 1996 (78/47) and 30 degrees in 1991 (82/52). There were no small spreads of up to seven degrees.

On the cool side, in 1984 the high was 60 with the record low of 29, a 31 degree spread. In 1993 the high was 61 with a low of 31, a 30 degree spread. The other cool high was 56 in 2003. Our only other 50s high was 59 three years ago in 2008. The other cool low was 36 in 2004 (our most recent 30s low). The other two 30s lows were 39 degrees, in 1992 and 2003. The record coolest high of 44 occurred way back in 1899, a time when the official readings were taken adjacent to Lake Michigan. 25 of the last 32 lows (78%) were in the: 40s (13) and 50s (12). There were three periods of consecutive 40s & 50s lows. The first was seven years from 1985 through 1991. The second was six years from 1996 through 2001. The third, and ongoing period is currently six years and began in 2005. Five lows were in the cold: 20s (1) and 30s (4). Two lows were in the warm 60s (65 in 1995 and 68 in 2002).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:21 and sunrise is at 6:49. Sunset is at 18:37 and twilight ends at 19:05. There's a total of 11 hours, 48 minutes of daylight today and 12 hours, 44 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:22 and sunrise is at 6:50. The moon is waxing crescent, heading towards first quarter in three days at 22:15. Illumination was 11% at midnight, will be 16% at noon and 20% at midnight tonight. Moonrise is at 10:54 this morning. Moonset is at 20:33 tonight. Moonrise is at 12:03 tomorrow afternoon. Moonlight time is 9 hours, 39 minutes which is 29 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 ten days.