September 4: ORD

Today is September 4th. It's the 248th day of the year. 118 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 79 and the normal low is 59. I've calculated the 33-year averages at 78 and 58.

On the hot side, in 1983 the high was the record high of 95 with a low of 67. That record high of 95 was originally set in 1954 and tied six years later in 1960. In 1990 the high was 91 (O'Hare's fourth hottest high of the date) with a low of 66. In 1999 the high was 92 (O'Hare's third hottest high of the date) with a low of 65. The only warm low (post-1978) was 71 degrees in 1985 (O'Hare's fourth warmest low of the date). The record warmest low of 74 degrees occurred in 1971. 18 of the past 33 highs (55%) were in the 70s. Nine highs (27%) were in the 80s. Three highs (9%) were in the hot 90s, most recently 92 degrees in 1999. Three highs (9%) were in the cool 60s, most recently 68 degrees two years ago in 2010. O'Hare's warmest September 4th was in 1960 as the high was 93 (O'Hare's second hottest high of the date) with a low of 72 (O'Hare's third warmest low of the date). O'Hare's second warmest September 4th was in 1971 as the high was 89 with a low of 74 (O'Hare's warmest low of the date). O'Hare's second warmest low of 73 degrees occurred in 1969. 

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1978 the high was 82 with a low of 52, a 30 degree spread. In 1974 the high was 68 with a cold low of 46, a cool day. In 1973 the high was 76 with a low of 69, a seven degree spread. In 1972 the low was a cold 47 degrees. In 1971 the high was 89 with a warm low of 74, a hot day and year of the record warmest low (74 at Midway). In 1969 the high was 76 with a warm low of 73, a mere three degree spread. In 1966 the high was 83 with a low of 53, a 30 degree spread. In 1963 the high was a cool 67 degrees. In 1962 the high was 85 with a low of 55, a 30 degree spread. In 1960 the high was 93 with a low of 72, a hot day.

More recently, there were large spreads of 32 degrees in 1982 (77/45) and  1987 (85/53). There was a small spread of six degrees in 2008 (67/61). In 2008 rain fell at a steady rate for most of the day. The clouds and moisture were courtesy of the remnants of Hurricane Gustov, dropping 2.91 inches of rain at O'Hare.

On the cool side, in 1997 (O'Hare's second coolest September 4th) the high was 71 with the co-record low of 45. Two years ago, in 2010, the high was 68 with a low of 51. In 1994 the high was 66 (O'Hare's coolest high of the date) with a low of 53. Tied with 1963 as O'Hare's second coolest high is the high of 67 degrees in 2008. The co-record low of 45 degrees occurred in 1982. Another cold low (which is tied with 1972 as O'Hare's third coldest low of the date) is 47 degrees in 1984. The record coolest high of 60 degrees occurred way back in 1902. 29 of the last 33 lows (88%) were in the: 50s (17) and 60s (12). Three lows were in the cold 40s. One low was in the warm 70s (71 in 1985). There were two long periods of lows in the 50s & 60s. The first was 11 years from 1986 through 1996. The second (which is ongoing) is 14 years from 1998 through last year, 2011. O'Hare's coolest September 4th was in 1974 as the high was 68 (O'Hare's third coolest high of the date) with a cold low of 46 (O'Hare's second coldest low of the date).  
 
The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:54 and sunrise is at 6:22. Sunset is at 19:21 and twilight ends at 19:50. There's a total of 12 hours, 59 minutes of daylight today and 13 hours, 56 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:55 and sunrise is at 6:23. The moon is waning gibbous. Illumination was 87% at midnight, will be 83% at noon and 79% at midnight tonight. Moonset is at 10:35 this morning. Moonrise is at 21:07 tonight. Moonset is at 11:34 tomorrow morning. Moonlight time is 13 hours, 28 minutes which is 29 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 five days. 9/11 Remembrance Day is in seven days. Today is the six year anniversary of the death of Steve Irwin, the Crocodile Hunter. Today in 2006, in what is described as a defensive act, a sting ray struck him in the heart with a poisonous barb during filming in an Australian choral reef.