October 30: ORD

Today is October 30th. It's the 304th day of the year. 62 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 61 and 40.

On the warm side, in 1999 the high was 76 (with 1974, O'Hare's second hottest high of the date) with a low of 56 (O'Hare's co-second warmest low of the date). A decade earlier, in 1989, the high was 75 with a low of 55. In 2004 the high was 72 with a low of 50. In 1990 the high was 73 with a low of 48. In 1998 the high was 65 with a low of 56 (O'Hare's co-second warmest low of the date). In 1981 the high was 75 with a low of 45, a 30 degree spread. The other warm highs were 72 degrees in 1987, 70 degrees in 2003, 70 degrees in 2006, 69 degrees in 1965 and 69 degrees in 1978. The record high of 85 degrees was set in 1950 at Midway. The record warmest low of 62 degrees occurred in 1974 at Midway. 28 of the past 33 highs (85%) were in the: 50s (8), 60s (12) and 70s (8). Three consecutive years (1983-1985) featured highs in the 50s. For 3 of 4 years, from 1987-1990 and from 2003-2006, highs were in the 70s. The more recent occurrence featured eight consecutive years (2003-2010) of highs in the 60s and 70s. Five highs were in the cold 40s. Our most recent 40s high was 48 degrees in 2002. O'Hare's warmest October 30th was in 1974 as the high was 76 (with 1999, O'Hare's second hottest high of the date) with a low of 62 (O'Hare's warmest and only 60s low of the date). O'Hare's second warmest October 30th was in 1971 as the high was 80 (O'Hare's hottest and only 80s high of the date) with a low of 55. 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 1978 the high was a warm 69 degrees. In 1976 the high was 49 with a low of 42, a seven degree spread. In 1974 the high was 76 with a low of 62, a warm day. 1974 was also the year of the record warmest low, also of 62 at Midway. In 1971 the high was 80 with a low of 55, a warm day. In 1968 the low was a cold 27 degrees. In 1966 the high was 52 with a cold low of 22, a 30 degree spread. In 1965 the high was a warm 69 degrees. In 1964 the high was 58 with a cold low of 24, a 34 degree spread. In 1963 the high was 58 with a cold low of 27, a 31 degree spread. In 1960 the low was a warm 51 degrees. 

More recently, there were large spreads of 36 degrees in 1987 (72/36), 32 degrees in 2006 (70/38), 31 degrees three years ago, in 2008 (62/31) and 30 degrees in 2003 (70/40). There were small spreads of four degrees in 1992 (46/42), five degrees in 1995 (45/40), five degrees in 2001 (52/47) and seven degrees in 2002 (48/41).

On the cold side, in 1988 (O'Hare's coolest October 30th) the high was 45 with the record low of 21. Five years later, in 1993 (O'Hare's second coolest October 30th), the high was 40 (O'Hare's coolest high of the date) with a low of 30. The other cold lows were 22 degrees in 1966 (O'Hare's second coldest low), 24 degrees in 1964, 24 degrees in 1980, 27 degrees in 1963 and 27 degrees in 1968. The other cold high was 45 degrees in 1995. The record coldest high of 28 degrees occurred back in 1917, 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: eight consecutive years from 1990 through 1997 and seven consecutive years from 2005 through last year, 2011. Two lows (6%) were in the cold 20s. The 20s lows occurred in the 1980s (24 degrees in 1980 and the record low of 21 degrees in 1988). Five lows (15%) were in the warm 50s, most recently 50 degrees in 2004.

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 45 with a low of 21, overall 15 degrees BELOW normal. Then in 1989 the high was 75 with a low of 55, overall 17 degrees ABOVE normal. 

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:56 and sunrise is at 7:25. Sunset is at 17:49 and twilight ends at 18:18. There's a total of 10 hours, 24 minutes of daylight today and 11 hours, 22 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:57 and sunrise is at 7:26. The moon is waning gibbous, having passed the full Hunter's moon yesterday at 14:49. Illumination was 100% at midnight, will be 99% at noon and 98% at midnight tonight. Moonset was at 8:13 this morning. Moonrise is at 18:16 tonight. Moonset is at 9:09 tomorrow morning. Moonlight time is 13 hours, 57 minutes which is 24 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 tomorrow. Standard Time returns in five days. Election Day is in seven days.