September 6: ORD

Today is September 6th. It's the 250th day of the year. 116 days remain. It's week 36 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 78 and the normal low is 59. I've calculated the 33-year averages at 80 and 59.

On the hot side, in 1990 (O'Hare's warmest September 6th) the high was 96 (O'Hare's hottest high of the date) with a low of 71. In 1985 (tied with 1960 as O'Hare's second warmest September 6th) the high was 93 (O'Hare's third hottest high of the date) with a low of 73 (one of O'Hare's two warmest lows of the date). In 1998 the high was 92 (tied with 1959 as O'Hare's fourth hottest high of the date) with a low of 70. O'Hare's other warmest low of 73 degrees occurred in 2007. The record high of 97 was set in 1960 after originally being set six years earlier in 1954 (both at Midway). The record warmest low of 78 occurred way back in 1881, at a time when the official readings were taken adjacent to Lake Michigan. 25 of the past 33 highs (76%) were in the: 70s (10) and 80s (15). Three highs (9%) were in the hot 90s. Five highs (15%) were in the cool 60s. For 12 consecutive years from 1999 through 2010, highs were in the 70s and 80s. In 1960 (tied with 1985 as O'Hare's second warmest September 6th) the high was 95 (O'Hare's second hottest high of the date) with a low of 71. O'Hare's second warmest lows of 71 degrees occurred in 1960, 1969 and 1990. O'Hare also had a hot high of 92 degrees in 1959 (tied with 1998 as O'Hare's fourth hottest high of the date).

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1976 the high was 83 with a cold low of 47, a 36 degree spread. In 1974 the low was a cold 46 degrees. In 1970 the high was 74 with a low of 67, a seven degree spread with 1.48 inches of rain. In 1969 the high was 78 with a warm low of 71, a seven degree spread with 1.32 inches of rain. In 1967 the high was 78 with a cold low of 45, a 33 degree spread. In 1963 the high was 77 with a cold low of 43, a 34 degree spread. In 1962 the high was 70 with a cold low of 43, a cool day. In 1960 the high was 95 with a low of 71, a hot day. 1960 was the year of the record high of 97 degrees at Midway. In 1959 the high was a hot 92 with a low of 69, a hot day.

More recently, there were additional large spreads of 31 degrees in 1991 (85/54) and 31 degrees in 2003 (81/50). There was a small spread of seven degrees in 1989 (75/68). 

On the cool side, in 1988 (O'Hare's coolest September 6th) the high was 66 (O'Hare's coolest high of the date, along with last year's 66 degree high) with a low of 43 (one of O'Hare's three second coldest lows of the date). Four years earlier, in 1984, the high was 73 with the record low of 42. Two years after that, in 1986, the high was 67 with a low of 49. The other post-1978 cold low was 47 degrees in 2000. The record coolest high of 61 degrees occurred way back in 1885, at a time when the official readings were taken adjacent to Lake Michigan. 25 of the last 33 lows (76%) were in the: 50s (14) and 60s (11). O'Hare recorded consecutive lows in the 50s and 60s as follows: seven from 1977 through 1983, seven from 1991 through 1997 and six from 2001 through 2006. Four lows (12%) were in the cold 40s. Four lows (12%) were in the warm 70s. O'Hare's second coolest September 6th was in 1962 as the high was 70 with a low of 43. The lows of 43 degrees in 1962, 1963 and 1988 are O'Hare's second coldest lows of the date. The other pre-1979 cold lows are 45 in 1967, 46 in 1974 and 47 in 1976.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:56 and sunrise is at 6:24. Sunset is at 19:18 and twilight ends at 19:46. There's a total of 12 hours, 54 minutes of daylight today and 13 hours, 50 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:57 and sunrise is at 6:25. The moon is waning gibbous. Illumination was 71% at midnight, will be 67% at noon and 62% at midnight tonight. Moonset is at 12:31 this afternoon. Moonrise is at 22:20 tonight. Moonset is at 13:26 tomorrow afternoon. Moonlight time is 14 hours, 11 minutes which is 19 minutes longer than yesterday.

Summer began on June 4th and runs for 110 days through September 21st. High temperatures in this period are usually in the 70s and 80s. Highs in the 60s, 90s and 100s occur infrequently. Grandparents Day is in three days. 9/11 Remembrance Day is in five days.