September 18: ORD

Today is September 18th. It's the 261st day of the year. 104 days remain. It's week 38 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 74 and the normal low is 53. I've calculated the 32-year averages at 75 and 53.

On the warm side, in 1985 the high was 87 with a low of 67. Three years later, in 1988, the high was 86 with a low of 67. In 2007 the high was 88 with a low of 63. In 1983 the high was 84 with a low of 65. The other warm high was 86 in 2000. The record high of 94 was set in 1955. The record warmest low of 71 occurred in 1965. Over the past 32 years, the tally of highs has been just about equal. Ten highs were in the 60s, 11 were in the 70s and 11 were in the 80s. In fact, O'Hare has never had a high in the 50s or 90s on September 18.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1978 the low was a warm 66 degrees. In 1977 the low was a warm 69 degrees. In 1976 the high was 78 with a low of 48, a 30 degree spread. In 1965 the high was 85 with a warm low of 68, a hot day and year of the record warmest low of 71 (at Midway). In 1963 the high was a hot 89 degrees. In 1962 the high was 75 with a low of 45, a 30 degree spread. In 1959 the low was a cold 40 degrees, which is equal to the record low.

More recently, there were large spreads of 35 degrees in 2000 (86/51), 31 degrees in 1984 (74/43), 30 degrees in 1980 (75/45) and 30 degrees in 1997 (83/53). There were small spreads of four degrees in 1986 (65/61) and seven degrees last year, in 2010 (65/58).

On the cool side, in 1981 the high was 60 with a low of 42. A decade later, in 1991, the high was 69 with a low of 42. The year prior, in 1990, the high was 63 with a low of 49. Five years later, in 1995, the high was 69 with a low of 44. In 1982 the high was 68 with a low of 45. The record low of 40 was set way back in 1889 and tied in 1901 and 1903. The record coolest high of 54 was set way back in 1901. These records were set when the official readings were taken adjacent to Lake Michigan. The last 40s low of 48 occurred 12 years ago in 1999. 17 of the last 32 lows (53%) were in the 50s. Nine lows (28%) were in the cold 40s. Six lows (19%) were in the warm 60s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:08 and sunrise is at 6:36. Sunset is at 18:58 and twilight ends at 19:26. There's a total of 12 hours, 22 minutes of daylight today and 13 hours, 18 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:09 and sunrise is at 6:37. The moon is waning gibbous. Illumination was 72% at midnight, will be 68% at noon and 63% at midnight tonight. Moonset is at 12:41 this afternoon. Moonrise is at 22:05 tonight. Moonset is at 13:35 tomorrow afternoon. Moonlight time is 14 hours, 36 minutes which is 14 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. Columbus Day is in 22 days.