September 29: ORD

Today is September 29th. It's the 272nd day of the year. 93 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 70 and 49.

On the warm side, in 1982 the high was 83 with a low of 63. In 2002 the high was 84 with a low of 60. In 1979 the high was 85 with a low of 58. In 1986 the high was 77 with a low of 64. Another warm high was 81 in 1983. The record high of 99 was set in 1953 and the record warmest low of 69 occurred way back in 1904, a time when the official readings were taken adjacent to Lake Michigan. 22 of the past 32 highs (69%) were in the: 60s (12) and 70s (10). There's been two notable streaks of 60s & 70s highs. The first was eight years from 1985 through 1992. The second was six years from 1996 through 2001. Six highs were in the warm 80s and four were in the cool 50s. Although there is not a rule, on three occasions the 50s & 80s have occurred in successive years. In 1983 the high of 81 was followed by a high of 55 in 1984. In 2002 the high of 84 was followed by a high of 58 in 2003. In 2006 the high of 59 was followed by a high of 80 in 2007. Another occurrence, although not perfect, was the high of 54 in 1993 which was followed by highs of 70 in 1994 and 80 in 1995.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1971 the high was 80 with a warm low of 65, a warm day. In 1970 the high was 72 with a low of 39, a 33 degree spread. In 1967 the high was a cold 47 with a low of 41, a six degree spread and cold day. In 1964 the high was 67 with a cold low of 32, a 35 degree spread. In 1962 the high was 66 with a cold low of 36, a 30 degree spread. In 1961 the high was 66 with a cold low of 32, a 34 degree spread. The lows of 32 in 1961 and 1964 are equal to the record.

More recently, there were large spreads of 31 degrees in 1983 (81/50) and 30 degrees in 2007 (80/50). There were no small spreads of up to seven degrees.

On the cool side, in 1984 the high was 55 with the record low of 32. In 1993 the high was 54 with a low of 37. The other cold low was 36 in 1992. The record coldest high of 44 was set way back in 1899, a time when the official readings were taken adjacent to Lake Michigan. 24 of the last 32 lows (75%) were in the: 40s (10) and 50s (14). For eight consecutive years, from 1994 through 2001, lows were in the 40s & 50s. Five lows were in the cold 30s and three were in the warm 60s. Today is also the runner-up date of the earliest first freeze which occurred in 1984. The earliest first freeze was on September 22, 1995.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:20 and sunrise is at 6:48. Sunset is at 18:39 and twilight ends at 19:07. There's a total of 11 hours, 51 minutes of daylight today and 12 hours, 47 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:21 and sunrise is at 6:49. The moon is waxing crescent, having passed new two days ago at 6:09. Illumination was 5% at midnight, will be 8% at noon and 11% at midnight tonight. Moonrise is at 9:39 this morning. Moonset is at 19:47 tonight. Moonrise is at 10:54 tomorrow morning. Moonlight time is 10 hours, 8 minutes which is 37 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 11 days.