October 7: ORD

Today is October 7th. It's the 281st day of the year. 85 days remain. It's week 41 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 of record 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 66 and the normal low is 45. I've calculated the 33-year averages at 66 and 45.

On the warm side, in 2007 (O'Hare's warmest October 7th) the high was the record high of 87 with the record warmest low of 67. The former record high of 86 degrees occurred in 1947 at Midway. The former record warmest low of  66 degrees occurred in 1914, at a time when the official readings were taken adjacent to Lake Michgan. A decade before 2007, in 1997 (O'Hare's second warmest October 7th), the high was 84 with a low of 63. In 1993 the high was 81 with a low of 58. Last year, in 2011, the high was 84 with a low of 54. Those highs of 84 degrees are O'Hare's second hottest highs of the date. In 1994 the high was 75 with a low of 61. 26 of the past 33 highs (79%) were in the: 50s (7), 60s (11) and 70s (8). O'Hare recorded 23 consecutive 50s, 60s and 70s highs from 1964 through 1986. Five highs were in the hot 80s and two were in the cold 40s. Both 40s highs were 49 degrees (in 1987 and 2000). O'Hare's third warmest October 7th was in 1970 as the high was 79 with a low of 63. O'Hare's other warm highs of the date are 81 degrees in 1963, 80 degrees in 2003 and 78 degrees in 1966. O'Hare's second warmest lows of the date are 63 degrees in 1970 and 1997. The other warm lows are 60 degrees in 1962, 60 degrees in 1984 and 57 degrees in 1959.

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 cool 54 degrees. In 1977 the high was a cool 53 degrees. In 1976 the high was a cool 50 degrees. In 1975 the high was 76 with a low of 43, a 33 degree spread. In 1974 the high was 54 with a low of 32, a cool day. In 1973 the low was a warm 58 degrees. In 1970 the high was 79 with a low of 63, a warm day. In 1966 the high was a warm 78 with a low of 47, a 31 degree spread. In 1964 the high was 68 with a cold low of 24, a 44 degree spread. That low of 24 is colder than the record low. In 1963 the high was a warm 81 with a low of 49, a 32 degree spread. In 1962 the low was a warm 60 degrees. In 1959 the high was 61 with a warm low of 57, a mere four degree spread.

More recently, there were large spreads of 39 degrees in 2003 (80/41), 35 degrees in 1985 (71/36), 33 degrees in 2004 (76/43), 33 degrees in 1980 (74/41) and 32 degrees in 1983 (77/45). There were small spreads of five degrees in 1984 (65/60), seven degrees in 1995 (53/46) and seven degrees three years ago, in 2008 (63/56).

On the cool side, in 2000 the high was 49 with a low of 30. In 1987 the high was also 49 with a low of 30. 1987 and 2000 are O'Hare's coolest October 7ths. Those highs of 49 degrees are O'Hare's coolest highs of the date. In 2001 the high was 52 with the record low of 29 (O'Hare's second coldest low of the date). The former record low of 30 degrees occurred in both 1987 and 2000. The record coolest high of 47 degrees occurred way back in 1896 at a time when the official readings were taken adjacent to Lake Michigan. 23 of the last 33 lows (70%) were in the: 30s (9) and 40s (14). O'Hare recorded ten consecutive 30s and 40s lows from 1974 through 1983. One low (3%) was in the cold 20s. Nine lows (27%) were in the warm: 50s (5) and 60s (4). Interestingly, the last 30s low was 12 years ago in 2000 (30 degrees) and the lone 20s low (the record low of 29 degrees) occurred a year later in 2001. Eight of the nine 30s lows (89%) occurred between 1979 and 1991. O'Hare's coldest low of the date is 24 degrees in 1964, a low colder than the record low. The other cold lows are 32 degrees in 1974 and 33 degrees in 1991. The other cool highs are 50 degrees in 1976, 53 degrees in 1977, 53 degrees in 1995 and 54 degrees in: 1974, 1978 and 2005.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:29 and sunrise is at 6:58. Sunset is at 18:24 and twilight ends at 18:52. There's a total of 11 hours, 26 minutes of daylight today and 12 hours, 23 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:31 and sunrise is at 6:59. The moon is waning gibbous, heading towards last quarter tomorrow at 2:33. Illumination was 60% at midnight, will be 56% at noon and 51% at midnight tonight. Moonset is at 13:39 this afternoon. Moonrise is at 23:31 tonight. Moonset is at 14:18 tomorrow afternoon. Moonlight time is 14 hours, 8 minutes which is 12 minutes shorter 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. Columbus Day is tomorrow. Standard Time doesn't return until November 4th.