August 29: ORD

Today is August 29th. It's the 241st day of the year. 124 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 61. I've calculated the 32-year averages at 81 and 61.

On the hot side, in 1984 the high was 94 with a low of 71. In 1991 the high was 92 with a low of 73. Last year, in 2010, the high was 94 with a low of 71. The other 90s highs were 94 in 1983 and 92 in 1980. The other 70s lows were 73 in 1995 and 70 in 2000. The record high of 98 was set in 1953. The record warmest low of 74 was set in 1973. 25 of the past 32 highs (78%) were in the: 70s (10) and 80s (15). Five highs were in the warm 90s and two highs were in the cool 60s (69 two years ago (in 2009) and 69 also in 2004). There were 12 straight years of highs in the 70s and 80s from 1992 through 2003.

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1973 the high was 92 with a low of 73, a hot day. 1973 was the year of the record warmest low. In 1971 the high was 84 with a low of 53, a 31 degree spread. In 1965 the high was 66 with a low of 41, a cool day. That low of 41 was colder than the record low. In 1964 the high was 83 with a low of 52, a 31 degree spread. In 1962 the high was a hot 92 with a low of 59, a 33 degree spread. In 1959 the temperatures for today (the 29th) and tomorrow (the 30th) were the same: a high of 86 with a low of 69.

More recently, there was a large spread of 30 degrees in 1983 (high of 94 and low of 64).

On the cool side, in 1986 the high was 71 with a low of 44. Four years earlier, in 1982, the high was 72 with the co-record low of 43. The record low of 43 was first set in 1965. Another cool low was 48 in 1988. As you can see, those 40s lows occurred quite some time ago from 1982 through 1988. The record coolest high of 62 occurred way back in 1893. 24 of the last 32 lows (75%) were in the: 50s (9) and 60s (15). Three lows were in the cool 40s. Five lows were in the warm 70s. For nine straight years, from 2001 to 2009, 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 5:46 and sunrise is at 6:15. Sunset is at 19:33 and twilight ends at 20:02. There's a total of 13 hours, 18 minutes of daylight today and 14 hours, 16 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:47 and sunrise is at 6:16. The moon is waxing crescent, having passed new yesterday at 22:04. Illumination was 0% at midnight, will be 1% at noon and 2% at midnight tonight. Moonrise is at 6:57 this morning. Moonset is at 19:31 tonight. Moonrise is at 8:13 tomorrow morning. Moonlight time is 12 hours, 34 minutes which is 46 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 seven days. 9/11 Remembrance Day and Grandparents Day are in 12 days.