September 1: ORD

Today is September 1st. It's the 244th day of the year. 121 days remain. It's week 35 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 80 and the normal low is 60. I've calculated the 32-year averages at 81 and 59.

On the hot side, in 2000 the high was 93 with a low of 67. A decade earlier, in 1990, the high was 89 with a low of 67. The other 90s highs were 96 in 1984 and 90 three years ago in 2008. Our warmest low was 71 last year in 2010. The record high of 101 was set in 1953. The record warmest low of 78 was set back in 1912. Another warm low was 76 in 1973 at Midway. 17 of the past 32 highs (53%) were in the 80s. Three highs (9%) were in the hot 90s. 12 highs (38%) were in the cool: 60s (3) and 70s (9).

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1973 the high was 91 with a warm low of 73, a hot day and year of the record warmest low. In 1967 the high was 72 with a cold low of 41 (colder than the record low), a 31 degree spread and cool day. In 1966 the high was 90 with a low of 60, a 30 degree spread. In 1963 the high was 82 with a low of 51, a 31 degree spread. In 1960 the high was 92 with a low of 73, a hot day.

More recently, there were large spreads of 39 degrees in 1984 (96/57), 30 degrees in 1997 (85/55) and 30 degrees in 1999 (85/55). There was a small spread of four degrees in 2003 (65/61).

On the cool side, in 1994 the high was 68 with a low of 50. Two years ago, in 2009, the high was 72 with a low of 47. That was just the second 40s low in O'Hare's history. The other was 41 in 1967. In 2001 the high was 67 with a low of 52. The other 60s high was 65 in 2003. There were three lows of 50 degrees (1987, 1992 and 1994). The record low of 45 was set way back in 1901 and then tied in 1949. The record coolest high of 62 occurred back in 1909. 30 of the last 32 lows (94%) were in the: 50s (15) and 60s (15). One low was in the 40s (47 in 2009) and one was in the 70s (71 in 2010).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:50 and sunrise is at 6:18. Sunset is at 19:28 and twilight ends at 19:56. There's a total of 13 hours, 10 minutes of daylight today and 14 hours, 6 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:51 and sunrise is at 6:19. The moon is waxing crescent. Illumination was 14% at midnight, will be 18% at noon and 23% at midnight tonight. Moonrise is at 10:45 this morning. Moonset is at 21:11 tonight. Moonrise is at noon tomorrow. Moonlight time is 10 hours, 26 minutes which is 40 minutes shorter 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. Labor Day is in four days. 9/11 Remembrance Day and Grandparents Day are in nine days.