October 23: ORD

Today is October 23rd. It's the 297th day of the year. 69 days remain. It's week 43 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. Before this, the official site was on the south side of Chicago at Midway International Airport (MDW), beginning on Wednesday, July 1, 1942. From Friday, January 1, 1926 through Tuesday, June 30, 1942, the official site was at the University of Chicago. Before this, the official site was at various locations in Chicago going back to Monday, October 16, 1871. Observations taken from October 15, 1870 to October 8, 1871 were lost in the Great Chicago Fire.

According to the National Climatic Data Center (NCDC), the normal high is 60 and the normal low is 41. I've calculated the 33-year averages at 59 and 42.

On the warm side, in 1992 the high was 76 with a low of 58. The year before, in 1991, the high was 77 with a low of 55. In 2004 the high was 76 (our most recent 70s high) with a low of 55. In 2000 the high was 71 with a low of 58. The following year of 2001 saw a  high of 65 with a low of 58, a seven degree spread. Those lows of 58 degrees in 1992, 2000 and 2001 are O'Hare's second warmest lows of the date. The other warm lows are 57 degrees in 1971, 55 degrees in 1986 and 54 degrees in: 1970, 1985 and two years ago, in 2010. The other warm highs were 75 degrees in 1973, 72 degrees in 1989 and 71 degrees in 1995. The record high of 85 degrees was set in 1963 at Midway. The record warmest low of 64 degrees occurred back in 1920, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the past 33 highs (79%) were in the: 40s (7), 50s (9) and 60s (10). O'Hare recorded consecutive highs in the 40s, 50s and 60s as: seven from 1982 through 1988 and seven from 2005 through last year, 2011. Six highs (18%) were in the warm 70s. One high (3%) was in the cold 30s (the record coolest high of 35 degrees in 1981). O'Hare's warmest October 23rd was in 1963 as the high was 85 (O'Hare's hottest and only 80s high of the date) with a low of 55. O'Hare's second warmest 10/23 was in 1975 as the high was 78 (with 1967, O'Hare's second warmest high of the date) with a low of 60 (O'Hare's warmest and only 60s low of the date). The other warm 10/23 was in 1967 as the high was 78 (with 1975, O'Hare's second warmest high of the date) and low of 54.    

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1975 the high was 78 with a low of 60, a warm day. In 1973 the high was a warm 75 with a low of 45, a 30 degree spread. In 1971 the high was 62 with a warm low of 57, a five degree spread. In 1970 the low was a warm 54 degrees. In 1969 the high was 48 with a low of 25, a cold day. In 1967 the high was 78 with a low of 54, a warm day. In 1964 the high was 53 with a cold low of 22 degrees, a 31 degree spread and a cool day. In 1963 the high was 85 with a low of 55, a 30 degree spread, a hot day and year of the record high, also of 85 at Midway. In 1963, 4 of 5 days from the 22nd to the 26th, highs were in the 80s. In 1962 the high was 47 with a low of 29, a cold day.

More recently, there were additional large spreads of 30 degrees in 1989 (72/42), 30 degrees in 1993 (68/38) and 30 degrees last year, in 2011 (68/38). There were additional small spreads of five degrees in 1983 (52/47), six degrees in 1979 (45/39) and six degrees in 2002 (46/40).

On the cool side, in 1981 (O'Hare's coolest October 23rd) the high was the record coolest high of 35 (O'Hare's only 30s high of the date) with the record low of 20. In the following year of 1982, the high was 54 with a low of 23 (O'Hare's third coldest low of the date). The other cold lows were 28 degrees in 1984 and 29 degrees in 1987. The other cool highs were 45 degrees in 1979, 46 degrees in 2002, 48 degrees in 1996 and 48 degrees in 2005. 29 of the last 33 lows (88%) were in the: 30s (11), 40s (10) and 50s (8). Four lows  were in the cold 20s. These 20s lows occurred within a span of seven years from 1981 to 1987. O'Hare's second coolest October 23rd was in 1969 as the high was 48 with a low of 25. The other cool days are 1964 (high of 53, low of 22 (O'Hare's second coldest low of the date)) and 1962 (high of 47, low of 29).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:47 and sunrise is at 7:16. Sunset is at 17:58 and twilight ends at 18:27. There's a total of 10 hours, 42 minutes of daylight today and 11 hours, 40 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:49 and sunrise is at 7:17. The moon is waxing gibbous, having reached first quarter two days ago at 22:32. Illumination was 62% at midnight, will be 67% at noon and 72% at midnight tonight. Moonset was at 1:01 this morning. Moonrise is at 14:47 this afternoon. Moonset is at 2:07 tomorrow morning. Moonrise is at 15:17 tomorrow afternoon. Moonlight time is 10 hours, 14 minutes which is 28 minutes longer than yesterday.

Warm Fall began September 22nd and runs for 41 days through November 1st. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the 30s and 40s occur infrequently. United Nations Day is tomorrow. Halloween is in eight days. Election Day is in 14 days. Standard Time doesn't return until November 4th.