September 11: ORD

Today is September 11th. It's the 254th day of the year. 111 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 77 and the normal low is 56. I've calculated the 32-year averages at 78 and 56.

On the hot side, in 2005 the high was 90 with a low of 69. In 1979 the high was 87 with a low of 65. Three years later, in 1982, the high was 88 with a low of 64. The record high of 95 was set in 1952. The record warmest low of 73 occurred in 1961. 27 of the past 32 highs (84%) were in the: 70s (14) and 80s (13). One high was in the hot 90s and four were in the cool 60s. For 11 consecutive years, from 1994 through 2004, highs were in the 70s & 80s.

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 90 with a low of 68, a hot day. In 1976 the high was 84 with a low of 53, a 31 degree spread. In 1974 the low was a warm 69 degrees. In 1967 the high was 71 with a cold low of 41, a 30 degree spread. That low of 41 was colder than the record low. In 1966 the high was 86 with a low of 49, a 37 degree spread. In 1964 the high was a cool 65 degrees. In 1962 the high was 80 with a low of 47, a 33 degree spread. In 1961 the high was 89 with a low of 68, a hot day and year of the record warmest low of 73 at Midway. In 1959 the high was a cool 65 degrees.

More recently, there were large spreads of 35 degrees in 1999 (81/46) and 30 degrees in 1988 (87/57). There was a small spread of seven degrees in 1991 (71/64).

On the cool side, in 1993 the high was 69 with the record low of 42. In the prior year of 1992, the high was 68 with a low of 47. In 1985 the high was 67 with a low of 49. The other cool 60s high was 67 in 2006. The record coolest high of 61 occurred in 1940, a time when the official readings were taken on the lakefront. The other cold 40s lows were 45 in 1995 and 46 in 1999. 27 of the last 32 lows (84%) were in the: 50s (16) and 60s (11). Five lows were in the cold 40s. No lows were in the warm 70s. For the last 11 years, since 2000, lows have been in the 50s & 60s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:01 and sunrise is at 6:29. Sunset is at 19:10 and twilight ends at 19:39. There's a total of 12 hours, 41 minutes of daylight today and 13 hours, 38 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:02 and sunrise is at 6:30. The moon is waxing gibbous, heading towards the full Harvest (a.k.a. Barley) moon tomorrow at 4:27. Illumination was 99% at midnight, will be 99% at noon and 100% at midnight tonight. Moonset is at 5:48 this morning. Moonrise is at 18:31 tonight. Moonset is at 6:48 tomorrow morning. Moonlight time is 11 hours, 17 minutes which is 37 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. 9/11 Remembrance Day and Grandparents Day are today.