September 7: ORD

Today is September 7th. It's the 250th day of the year. 115 days remain. It's week 36 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 78 and the normal low is 58. I've calculated the 32-year averages at 79 and 59.

On the hot side, in 1985 the high was 99 with a low of 73. In 2001 the high was 87 with a low of 68. Four years later, in 2005, the high was 88 with a low of 67. Other hot 90s highs were 90 in 1984 and 90 in 1991 (our most recent). The other warm 70s low was 70 in 2007. The record high of 100 was set in 1960 at Midway International Airport, this after being originally set in the city in 1939. The record warmest low of 78 occurred way back in 1922, a time when the thermometer was located adjacent to Lake Michigan. 25 of the past 32 highs (78%) were in the: 70s (14) and 80s (11). Three highs were in the hot 90s. Four highs were in the cool 60s, most recently 68 in 1995. There's been an ongoing, 15-year stretch of highs in the 70s & 80s that began in 1996 and went through last year, 2010.

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 degrees. In 1972 the high was 74 with a low of 68, a six degree spread. In 1971 the high was a hot 92 with a low of 68, a hot day. In 1970 the high was 88 with a warm low of 73, a hot day. In 1968 the high was 79 with a low of 47, a 32 degree spread. In 1967 the high was 80 with a cold low of 44, a 36 degree spread. In 1966 the high was 76 with a cold low of 45, a 31 degree spread. In 1964 the high was a hot 94 with a low of 65, a hot day. There's also another interesting thing about 1964: on the 5th the low was 46, so there was an incredible 48 degree swing to a high of 94 today. In 1962 the high was 78 with a cold low of 39, a 39 degree spread. That low of 39 was colder than the record low. In 1960 the high was 99 with a low of 73, a hot day. 1960 was the year of the record high of 100 degrees, occurring at Midway. In 1959 the high was 96 with a low of 74, a hot day.

More recently, there were large spreads of 33 degrees in 1988 (77/44), 30 degrees in 1999 (80/50) and 30 degrees in 2002 (89/59). There were no small spreads of up to seven degrees.

On the cool side, in 1986 as the high was 66 with the record low of 42. In 1979 the high was 66 with a low of 53. The other cold 40s lows were 44 in 1988 and 49 in 1993 (our most recent). The other cool 60s highs were 68 in 1995 (our most recent) and 69 in 1982. The record coolest high of 61 occurred way back in 1924, a time when the thermometer was located adjacent to Lake Michigan. 27 of the last 32 lows (84%) were in the: 50s (15) and 60s (12). Three lows were in the cold 40s and two were in the warm 70s. For 13 straight years, from 1994 through 2006, lows were in the 50s and 60s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:56 and sunrise is at 6:25. Sunset is at 19:17 and twilight ends at 19:46. There's a total of 12 hours, 52 minutes of daylight today and 13 hours, 50 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:57 and sunrise is at 6:26. The moon is waxing gibbous. Illumination was 76% at midnight, will be 80% at noon and 84% at midnight tonight. Moonset is at 1:36 this morning. Moonrise is at 16:39 this afternoon. Moonset is at 2:41 tomorrow morning. Moonlight time is 8 hours, 57 minutes which is 23 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 in four days.