September 12: ORD

Today is September 12th. It's the 255th day of the year. 110 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.

According to the National Climatic Data Center (NCDC), the normal high is 76 and the normal low is 56. I've calculated the 32-year averages at 79 and 57.

On the hot side, in 2005 the high was 90 with a low of 68. In 1988 the high was 85 with a low of 67. In 1994 the high was 87 with a low of 65. In 1979 the high was 87 with a low of 64. Another warm high was 88 in 1998. The record high of 96 was set in 1952. The record warmest low of 72 occurred back in 1931, a time when the official readings were taken adjacent to Lake Michigan. 27 of the past 32 highs (84%) were in the: 70s (13) and 80s (14). One high was in the hot 90s and four were in the cool 60s.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1975 the high was 61 with a low of 43, a cool day. That low of 43 is colder than the record low of 44. In 1973 the high was 76 with a low of 46, a 30 degree spread. In 1972 the high was 70 with a low of 64, a six degree spread. In 1967 the high was 79 with a cold low of 41, a 38 degree spread. That low of 41 is colder than the record low of 44. In 1966 the high was 84 with a low of 52, a 32 degree spread. In 1964 the high was 65 with a cold low of 38, a cool day. That low of 38 is colder than the record low of 44. In 1962 the high was a hot 91 degrees. In 1961 the low was a warm 68 degrees. In 1960 the high was a cool 62 degrees.

More recently, there were no large spreads of at least 30 degrees or more. There was a small spread of four degrees three years ago in 2008 (73/69).

On the cool side, in 1985 the high was 66 with a low of 46. In 2007 the high was 67 with a low of 46. The other cold 40s lows were 48 in 1992, 48 in 1997 and 49 in 2002. The record low of 44 was set in 1955. The other cool 60s highs were 67 in 1989 and 67 in 1996. The record coolest high of 53 occurred in 1902, a time when the official readings were taken adjacent to Lake Michigan. 27 of the last 32 lows (84%) were in the: 50s (14) and 60s (13). Five lows were in the cold 40s. No lows were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:02 and sunrise is at 6:30. Sunset is at 19:09 and twilight ends at 19:37. There's a total of 12 hours, 39 minutes of daylight today and 13 hours, 35 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:03 and sunrise is at 6:31. The moon is full today as the full Harvest (a.k.a. Barley) moon at 4:27. Illumination was 100% at midnight, will be 100% at noon and 99% at midnight tonight. Moonset is at 6:48 this morning. Moonrise is at 18:55 tonight. Moonset is at 7:48 tomorrow morning. Moonlight time is 11 hours, 53 minutes which is 36 minutes longer 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. Citizenship Day is in five days.