September 5: ORD

Today is September 5th. It's the 248th day of the year. 117 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 79 and the normal low is 59. I've calculated the 32-year averages at 80 and 57.

On the hot side, in 1983 the high was 95 with a low of 68. Two years later, in 1985, the high was 92 with a low of 71. The other 90s highs were 92 in 1999, 90 in 1995 and 90 in 2007 (our most recent). The record high of 98 was set way back in 1899. The record warmest low of 77 occurred way back in 1912. The other 70s low was 71 in 1990. 23 of the past 31 highs (72%) were in the: 70s (10) and 80s (13). Our most recent 80s high was 87 in 2005. Five highs (16%) were in the hot 90s. Four highs (12%) were in the cool 60s, most recently 67 in 2000.

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 88 with a low of 57, a 31 degree spread. In 1975 the high was a cool 67 degrees. In 1974 the high was 72 with a cold low of 42, a 30 degree spread. In 1969 the low was a warm 72 degrees. In 1967 the high was 78 with a low of 48, a 30 degree spread. In 1964 the high was 79 with a cold low of 46, a 33 degree spread. In 1962 the high was 67 with a low of 42, a cool day. In 1959 the high was a hot 92 degrees. In 1959, today was the start of five straight days of highs in the 90s.

More recently, there were large spreads of 35 degrees in 1998 (87/52), 30 degrees in 1987 (88/58) and 30 degrees in 1999 (92/62). There was a small spread of seven degrees in 1994 (65/58).

On the cool side, in 1988 the high was 64 with the co-record low of 44. Four years earlier, in 1984, the high was 69 with the co-record low of 44. The other 60s highs were 65 in 1994 and 67 in 2000. The other 40s lows were 48 in 1997, 48 in 2003 and 49 last year (in 2010). The record coolest high of 62 occurred way back in 1909. 17 of the last 32 lows (53%) were in the 50s. Five lows (16%) were in the cool 40s. Ten lows (31%) were in the warm: 60s (8) and 70s (2). The most recent 70s lows were 71 in 1990 and 71 five years earlier in 1985.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:54 and sunrise is at 6:23. Sunset is at 19:21 and twilight ends at 19:49. There's a total of 12 hours, 58 minutes of daylight today and 13 hours, 55 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:55 and sunrise is at 6:24. The moon is waxing gibbous and reached first quarter yesterday at 12:39. Illumination was 56% at midnight, will be 61% at noon and 66% at midnight tonight. Moonrise is at 15:11 this afternoon. Moonset is at 0:33 tomorrow morning. Moonrise is at 15:59 tomorrow afternoon. Moonlight time is 8 hours, 49 minutes which is 30 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 today. 9/11 Remembrance Day and Grandparents Day are in six days.