September 25: ORD

Today is September 25th. It's the 268th day of the year. 97 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 71 and the normal low is 50. I've calculated the 32-year averages at 70 and 49.

On the warm side, in 1986 the high was 88 with a low of 68. In 2007 the high was 85 with a low of 63. Other warm lows were 67 in 2005 and 63 three years ago in 2008. The record high of 90 was set back in 1933 and the record warmest low of 72 occurred in 1920, in both cases at a time when the official readings were taken adjacent to Lake Michigan. 21 of the past 31 highs (66%) were in the: 60s (8) and 70s (13). For seven consecutive years, from 1991-1997, highs were in the 60s & 70s. Six highs (19%) were in the warm 80s. Five highs (15%) 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 1975 the high was a cool 59 with a low of 52, a seven degree spread. In 1973 the high was 80 with a warm low of 69, a warm day. In 1972 the high was 74 with a warm low of 68, a six degree spread. In 1971 the high was a cool 58 with a low of 51, a seven degree spread. In 1967 the high was 73 with a low of 40, a 33 degree spread. In 1964 the high was 74 with a low of 40, a 34 degree spread. In 1963 the high was a warm 83 with a low of 52, a 31 degree spread. In 1961 the high was a cool 56 with a low of 42, a cool day. In 1959 the high was 85 with a low of 63, a hot day.

More recently, there were large spreads of 37 degrees in 1999 (80/43), 34 degrees in 1984 (74/40), 32 degrees in 1988 (77/45), 31 degrees in 1989 (70/39), 31 degrees in 2002 (74/43) and 30 degrees in 1998 (81/51). There was a small spread of three degrees in 1983 (58/55).

On the cool side, in 1985 the high was 58 with a low of 35. In 2000 the high was 55 with a low of 43. In 2001 the high was 58 with a low of 40. In 1982 the high was 52 with a low of 47, a five degree spread. The other cool high was 58 in 1983. The record low of 30 and record coolest high of 46 were set on the same cold day in 1942. 25 of the last 32 lows (78%) were in the: 40s (15) and 50s (10). 15 consecutive 40s & 50s lows occurred from 1990 through 2004. Two lows were in the cold 30s (1985 & 1989). Five lows were in the warm 60s (four of them bunched together in 2005, 2007, 2008 and 2009).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:16 and sunrise is at 6:44. Sunset is at 18:46 and twilight ends at 19:14. There's a total of 12 hours, 2 minutes of daylight today and 12 hours, 58 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:17 and sunrise is at 6:45. The moon is waning crescent. Illumination was 7% at midnight, will be 5% at noon and 2% at midnight tonight. Moonrise is at 4:29 this morning. Moonset is at 17:27 this afternoon. Moonrise is at 5:45 tomorrow morning. Moonlight time is 12 hours, 58 minutes which is 42 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 15 days.