October 24: ORD

Today is October 24th. It's the 298th day of the year. 68 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 59 and the normal low is 41. I've calculated the 33-year averages at 57 and 40.

On the warm side, in 1991 (O'Hare's warmest October 24th) the high was 74 with the record warmest low of 63. Two years prior, in 1989, the high was 76 (O'Hare's third hottest high) with a low of 51. Two years ago, in 2010, the high was 72 with a low of 54. In 2000 the high was 67 with a low of 58. The other warm highs were 74 degrees in 1975, 71 degrees in 1974 and 71 degrees in 1985. We went 19 years, from 1991 to 2010, between highs in the 70s. The other warm low was 54 degrees in 1986. The record high of 83 degrees was set in 1963 at Midway. 22 of the past 33 highs (67%) were in the: 50s (13) and 60s (9). Four highs (12%) were in the warm 70s. Seven highs (21%) were in the cold 40s. O'Hare's second warmest October 24th was in 1963 as the high was 82 (O'Hare's hottest high of the date) with a low of 53. O'Hare's other warm days were in: 1973 (high of 78 (O'Hare's second hottest high of the date), low of 53)), 1970 (high of 72, low of 53) and 1971 (high of 64, low of 61 (O'Hare's second warmest low of the date)). UPDATE: O'Hare had a high of 78 degrees today (10/24/12) which ties 1973 as the second hottest high of the date.  

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1976 the high was 49 with a low of 43, a six degree spread. In 1975 the high was a warm 74 with a low of 47, a warm day. In 1974 the high was a warm 71 degrees. In 1973 the high was 78 with a low of 53, a warm day. In 1972 the high was a cold 42 with a low of 40, a two degree spread. In 1971 the high was 64 with a warm low of 61, a three degree spread and warm day. In 1970 the high was 72 with a low of 53, a warm day. In 1966 the high was 60 with a cold low of 28, a 32 degree spread. In 1964 the high was 62 with a cold low of 24, a 38 degree spread. In 1963 the high was 82 with a low of 53, a warm day and year of the record high of 83 at Midway. In 1962 the high was 45 with a low of 25, a cold day. In 1960 the high was 43 with a low of 29, a cold day.

More recently, there was a large spread of 34 degrees in 1982 (57/23). There were small spreads of four degrees in 1983 (51/47), four degrees in 1986 (58/54), four degrees in 2002 (46/42) and six degrees in 1997 (49/43).

On the cool side, in 1981 (O'Hare's coolest October 24th) the high was the co-record coolest high of 40 with the record low of 17. In 1988 (O'Hare's second coolest October 24th) the high was the co-record coolest high of 40 with a low of 26. The other cold lows were 23 degrees in 1982 (O'Hare's second coldest low of the date), 24 degrees in 1964 (O'Hare's third coldest low of the date), 28 degrees in 1966, 28 degrees in 1984 and 28 degrees in 1999 (our most recent 20s low). The other cool highs are 42 degrees in 1972 (O'Hare's second coolest high of the date) and 46 degrees in 2002. 23 of the last 33 lows (70%) were in the: 30s (9) and 40s (14). There were two long stretches of lows in the 30s and 40s. The first was seven years from 1992 through 1998. The second was nine years from 2001 through 2009. Five lows (15%) were in the cold: 10s (1) and 20s (4).  Five lows (15%) were in the warm: 50s (4) and 60s (1). O'Hare's other cool days were in: 1962 (high of 45, low of 25) and 1960 (high of 43, low of 29).

There's an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1988 the high was 40 (the record coldest high) with a low of 26, overall 17 degrees BELOW normal. Then in 1989 the high was 76 with a low of 51, overall 13.5 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:49 and sunrise is at 7:17. Sunset is at 17:57 and twilight ends at 18:26. There's a total of 10 hours, 40 minutes of daylight today and 11 hours, 37 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:50 and sunrise is at 7:18. The moon is waxing gibbous. Illumination was 72% at midnight, will be 77% at noon and 81% at midnight tonight. Moonset was at 2:07 this morning. Moonrise is at 15:17 this afternoon. Moonset is at 3:10 tomorrow morning. Moonrise is at 15:45 tomorrow afternoon. Moonlight time is 10 hours, 50 minutes which is 36 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 today. Halloween is in seven days. Standard Time returns in 11 days. Election Day is in 13 days.