September 9: ORD

Today is September 9th. It's the 253rd day of the year. 113 days remain. It's week 37 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 57. I've calculated the 33-year averages at 78 and 58.

On the hot side, in 1983 (O'Hare's warmest September 9th) the high was the record high of 95 with a low of 70. That record high of 95 also occurred in 1959 and originally four years before in 1955 (both at Midway). In 1991 (O'Hare's second warmest September 9th) the high was 94 (with 1964, O'Hare's second hottest high of the date) with a low of 70 (our most recent 70s low). Those lows of 70 degrees are O'Hare's warmest lows of the date. In 2002 the high was 90 (our most recent 90s high) with a low of 66. The record warmest low of 75 occurred way back in 1912, a time when the official readings were taken adjacent to Lake Michigan. 26 of the past 33 highs (79%) were in the: 70s (16) and 80s (10). Three highs were in the hot 90s. Four highs were in the cool 60s. The pre-1979 warm days are 1971 (high of 90 with O'Hare's second warmest low of 69 degrees) and 1978 (O'Hare's third hottest high of 93 with a low of 65). The other hot highs were 94 degrees in 1964 (tied with 1991 as O'Hare's second hottest high of the date) and 90 degrees in 1959.

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 a hot 93 with a low of 65, a hot day. In 1971 the high was 90 with a low of 69, a hot day. In 1966 the high was 82 with a cold low of 45, a 37 degree spread. In 1964 the high was a hot 94 with a low of 62, a 32 degree spread. In 1963 the high was 85 with a low of 54, a 31 degree spread. In 1959 the high was a hot 90 degrees.

More recently, there were large spreads of 34 degrees in 1982 (81/47), 31 degrees in 1988 (81/50) and 30 degrees in 1981 (75/45). There was a small spread of seven degrees in 2006 (70/63). 

On the cool side, in 1986 (tied with 1969 and 1975 as O'Hare's coolest September 9ths) the high was 73 with the record low of 43, a 30 degree spread. Two years ago, in 2010, the high was 67 (O'Hare's co-coolest high of the date) with a low of 50. In 1995 the high was 69 with a low of 48. The other co-coolest high of 67 degrees occurred in 1992. The other cold low of  45 degrees occurred in 1981 (tied with 1966 as O'Hare's second coldest lows of the date). The record coolest high of 56 degrees occurred way back in 1883, a time when the official readings were taken adjacent to Lake Michigan. 25 of the last 33 lows (76%) were in the: 50s (12) and 60s (13). Six lows were in the cold 40s. Two lows were in the warm 70s. For 12 consecutive years, from 1996 through 2007, lows were in the 50s & 60s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:59 and sunrise is at 6:28. Sunset is at 19:13 and twilight ends at 19:41. There's a total of 12 hours, 45 minutes of daylight today and 13 hours, 42 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:00 and sunrise is at 6:29. The moon is waning crescent, having reached last quarter yesterday at 8:15. Illumination was 43% at midnight, will be 39% at noon and 34% at midnight tonight. Moonset is at 15:03 this afternoon. Moonrise is at 0:45 tomorrow. Moonset is at 15:45 tomorrow afternoon. Moonlight time is 15 hours, 3 minutes which is 38 minutes longer than yesterday. Moonlight time is at its peak today and tomorrow.

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 today. 9/11 Remembrance Day is in two days.