September 4: ORD

Today is September 4th. It's the 247th 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.

According to the National Climatic Data Center (NCDC), the normal high is 79 and the normal low is 59. I've calculated the 32-year averages at 79 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 with a low of 66. In 1999 the high was 92 (our most recent 90s high) with a low of 65. Our only 70s low was 71 in 1985. The record warmest low of 74 occurred in 1971. 26 of the past 32 highs (81%) were in the: 70s (17) and 80s (9). Three highs were in the hot 90s and three were in the cool 60s, most recently 68 last year (in 2010).

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 32 degrees in 1987 (85/53). There was a small spread of six degrees in 2008 (67/61). Three years ago, 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 the high was 71 with the co-record low of 45. Last year, in 2010, the high was 68 with a low of 51. In 1994 the high was 66 with a low of 53. A decade earlier, in 1984, the high was 73 with a low of 47. Another cool high was 67 three years ago, in 2008. The co-record low of 45 occurred in 1982. The record coolest high of 60 occurred way back in 1902. 28 of the last 31 lows (88%) were in the: 50s (16) and 60s (12). Three lows were in the cool 40s and one 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 13 years from 1998 through last year (2010).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:53 and sunrise is at 6:22. Sunset is at 19:23 and twilight ends at 19:51. There's a total of 13 hours, 1 minute of daylight today and 13 hours, 58 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:54 and sunrise is at 6:23. The moon reaches first quarter today at 12:39. Illumination was 45% at midnight, will be 50% at noon and 56% at midnight tonight. Moonrise is at 14:15 this afternoon. Moonset is at 23:34 tonight. Moonrise is at 15:11 tomorrow afternoon. Moonlight time is 9 hours, 19 minutes which is 10 minutes shorter than yesterday.

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