September 10: ORD

oday is September 10th. It's the 253rd day of the year. 112 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 57. I've calculated the 32-year averages at 79 and 58.

On the hot side, in 1983 the high was the record high of 95 with a low of 67. Three years later, in 1986, the high was 90 with a low of 70. In 2005 the high was 92 with a low of 67. In 2000 the high was 84 with a low of 72, our most recent 70s low. Another warm high was 89 degrees in 2002. The record warmest low of 75 occurred way back in 1912, a time when the thermometer was located adjacent to Lake Michigan. 24 of the past 32 highs (75%) were in the: 70s (11) and 80s (13). Three highs were in the hot 90s and five were in the cool 60s. In 1996, today was the last day of a high in the 80s, the earliest day of the past 32 years. For nine consecutive years, from 1996 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 a hot 92 with a low of 65, a hot day. In 1972 the high was a cool 64 degrees. In 1971 the low was a warm 69 degrees. In 1968 the high was a cool 61 with a low of 55, a six degree spread. In 1967 the high was 65 with a low of 45, a cool day. In 1966 the high was 84 with a low of 47, a 37 degree spread. In 1964 the high was a hot 93 with a low of 65, a hot day. In 1961 the high was a hot 89 degrees. In 1959 the high was a cool 65 degrees.

More recently, there was a large spread of 36 degrees in 1988 (86/50) and a small spread of four degrees in 2006 (64/60).

On the cool side, in 1995 the high was 64 with a low of 46, our coldest low. That high of 64 shares the 64 degree high in 2006 as our coolest highs. In 1993 the high was 65 with a low of 47. The other cool 60s highs were 68 in 1992 and 69 in 1985. The other cold 40s lows were all 48 degrees: in 1998, 1999 and three years ago, in 2008. The record low of 44 was set in 1943. The record coolest high of 53 occurred way back in 1917, a time when the thermometer was located adjacent to Lake Michigan. 25 of the last 32 lows (78%) were in the: 50s (11) and 60s (14). Five lows were in the cold 40s and two were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:59 and sunrise is at 6:28. Sunset is at 19:12 and twilight ends at 19:40. There's a total of 12 hours, 44 minutes of daylight today and 13 hours, 41 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:01 and sunrise is at 6:29. The moon is waxing gibbous, heading towards the full Harvest (a.k.a. Barley) moon in two days at 4:27. Illumination was 96% at midnight, will be 97% at noon and 99% at midnight tonight. Moonset is at 4:47 this morning. Moonrise is at 18:07 tonight. Moonset is at 5:48 tomorrow morning. Moonlight time is 10 hours, 40 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 tomorrow.