September 13: ORD

Today is September 13th. It's the 256th day of the year. 109 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 77 and 58.

On the hot side, in 2005 the high was 94 with a low of 71. In 1994 the high was 88 with a low of 66. Another hot high was 90 in 1998. Other warm lows were 70 in 1982 and 68 (1993, 2003 and three years ago in 2008). The record high of 98 was set back in 1939. The record warmest low of 75 occurred back in 1927, a time when the official readings were taken adjacent to Lake Michigan. 23 of the past 32 highs (72%) were in the: 70s (11) and 80s (12). Two highs (6%) were in the hot 90s and seven (22%) 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 63 with a low of 40, a cool day. In 1974 the high was 59 with a low of 44, a cool day. In 1970 the high was a cool 59 with a low of 52, a seven degree spread. In 1964 the high was 70 with a cold low of 37, a 33 degree spread and cool day. That low of 37 was colder than the record low. In 1963 the high was 62 with a low of 43, a cool day. In 1962 the high was 91 with a low of 71, a hot day.

More recently, there were large spreads of 33 degrees in 1998 (90/57) and 32 degrees in 2000 (79/47). There were small spreads of five degrees in 2006 (65/60) and seven degrees three years ago, in 2008 (75/68). Three years ago, in 2008, we were getting lots of rain from the remnants of Hurricane Ike. O'Hare recorded 6.64 inches of rain, a new record for September 13.

On the cool side, in 1985 the high was 64 with a low of 42. In 1996 the high was 64 with a low of 48. In 1989 the high was 60 with a low of 53, a seven degree spread. The other cool 60s highs were 65 in 2006, 66 in 1999, 67 in 1983 and 68 in 2001. The record coolest high of 55 occurred way back in 1880, a time when the official readings were taken adjacent to Lake Michigan. The other cold 40s lows were 47 in 2000, 48 in 1983 and 48 in 1987. The record low of 39 was set way back in 1890, a time when the official readings were taken adjacent to Lake Michigan. 25 of the last 32 lows (78%) were in the: 50s (13) and 60s (12). Five lows (16%) were in the cold 40s and two (6%) were in the warm 70s (71 in 2005 and 70 in 1982). For eight consecutive years, from 1988 through 1995, lows were in the 50s & 60s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:03 and sunrise is at 6:31. Sunset is at 19:07 and twilight ends at 19:35. There's a total of 12 hours, 36 minutes of daylight today and 13 hours, 32 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:04 and sunrise is at 6:32. The moon is waning gibbous and was full yesterday as the full Harvest (a.k.a. Barley) moon at 4:27. Illumination was 99% at midnight, will be 98% at noon and 97% at midnight tonight. Moonset is at 7:48 this morning. Moonrise is at 19:19 tonight. Moonset is at 8:47 tomorrow morning. Moonlight time is 12 hours, 29 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 four days.