October 29: ORD

Today is October 29th. It's the 303rd day of the year. 63 days remain. It's week 44 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 that, 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 57 and the normal low is 39. I've calculated the 33-year averages at 58 and 39.

On the warm side, in 2004 (O'Hare's warmest October 29th) the high was 76 (O'Hare's second hottest high of the date) with a low of 61 (O'Hare's warmest low of the date). The low was also 61 degrees in 1900. In 1989 (O'Hare's second warmest October 29th) the high was 74 with a low of 54. A couple of years later, in 1991, the high was 70 with a low of 55. In 1999 the high was the record high of 78 with a low of 45, a 33 degree spread. The other warm highs were 72 degrees in 1971 and 69 degrees in 1979. The record warmest low of 65 degrees was set in 1946 at Midway. 23 of the past 33 highs (70%) were in the: 50s (12) and 60s (11). Highs were in the 50s and 60s for: seven consecutive years from 1981 through 1987 and seven consecutive years from 2005 through last year, 2011. Four highs (12%) were in the warm 70s. Six highs (18%) were in the cold: 30s (1) and 40s (5). The last highs in the 40s and 70s came in back to back years (48 degrees in 2003 and 76 degrees in 2004). O'Hare's other warm days occurred in: 1961 (high of 70, low of 55) and 1974 (high of 64 and O'Hare's second warmest low of the date of 57). The other warm low of 51 degrees occurred in 1960.

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1974 the high was 64 with a warm low of 57, a seven degree spread and warm day. In 1973 the high was 49 with a low of 44, a five degree spread. In 1971 the high was a warm 72 degrees. In 1966 the high was 48 with a cold low of 24, a cool day. In 1965 the high was 55 with a cold low of 22 degrees, a 33 degree spread. In 1964 the low was a cold 27 degrees. In 1963 the high was 57 with a cold low of 27, a 30 degree spread. In 1961 the high was 70 with a low of 55, a warm day. In 1960 the high was 58 with a warm low of 51, a seven degree spread.

More recently, there were additional large spreads of 33 degrees in 2005 (61/28), 31 degrees in 1984 (61/30) and 30 degrees in 1990 (60/30). There were small spreads of four degrees in 2002 (46/42) and six degrees in 1992 (48/42).

On the cool side, in 1988 (O'Hare's coolest October 29th) the high was 41 (O'Hare's second coolest high of the date) with a low of 25. Five years later, in 1993 (O'Hare's second coolest October 29th), the high was 39 (O'Hare's coolest and only 30s high of the date) with a low of 30. In 1980 the high was 47 with a low of 25. Those lows of 25 degrees (1980 and 1988) are O'Hare's co-third coldest lows. The record low of 19 degrees and record coolest high of 29 degrees were set on the same cold day back in 1925, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 30s (14) and 40s (12). Lows were in the 30s and 40s for: seven consecutive years from 1981 through 1987, six consecutive years from 1998 through 2003 and six consecutive years from 2006 through last year, 2011. Four lows (12%) were in the cold 20s. Three lows (9%) were in the warm: 50s (2) and 60s (1). The last lows in the 60s and 20s came in back to back years (61 degrees in 2004 and 28 degrees in 2005). O'Hare's other cool day was in 1966 (high of 48 and O'Hare's second coldest low of the date of 24). O'Hare's other cold lows are 22 degrees in 1965 (O'Hare's coldest low of the date) and 27 degrees in 1963.

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 41 with a low of 25, overall 15 degrees BELOW normal. Then in 1989 the high was 74 with a low of 54, overall 16 degrees ABOVE normal. 

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:54 and sunrise is at 7:23. Sunset is at 17:50 and twilight ends at 18:19. There's a total of 10 hours, 27 minutes of daylight today and 11 hours, 25 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:56 and sunrise is at 7:25. The moon reaches the full Hunter's moon today at 14:49. Illumination was 100% at midnight, will be 100% at noon and 100% at midnight tonight. Moonset was at 7:14 this morning. Moonrise is at 17:41 this afternoon. Moonset is at 8:13 tomorrow morning. Moonlight time is 13 hours, 33 minutes which is 27 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. Halloween is in two days. Standard Time returns in six days. Election Day is in eight days.