July 29: ORD

Today is July 29th. It's the 210th day of the year. 155 days remain. It's week 30 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 84 and the normal low is 64. I've calculated the 32-year averages at 84 and 63.

On the hot side, in 1983 the high was 96 with a low of 72. In 2006 the high was 94 (our most recent 90s high) with a low of 74. In 1988 the high was 97 with a low of 70. In 1999 the high was 96 with a low of 69. In 1995 the high was 95 with a low of 69. The other 90s highs were 91 in 1987 and 90 in 2001. The record high of 99 was set back in 1913. The other 70s lows were 73 in 1990 and 71 in 2002. The record warmest low of 85 occurred back in 1916. We had very high dew points in 1999. The top was 82 degrees, making 1999 perhaps the most humid July 29 on record. 17 of the last 32 highs (53%) were in the 80s. Seven highs (22%) were in the hot 90s. Eight highs (25%) were in the cool 70s. Our most recent 70s high was 79 in 2000. There is an interesting phenomenon. In the year following a high of at least 95 degrees, the high is 16 or 17 degrees cooler. The four instances so far: 1983 (96) followed by 1984 (79), 17 degrees cooler; 1988 (97) followed by 1989 (81), 16 degrees cooler; 1995 (95) followed by 1996 (78), 17 degrees cooler; 1999 (96) followed by 2000 (79), 17 degrees cooler.

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1971 the low was a cool 52 degrees. In 1965 the high was 80 with a cool low of 50, a 30 degree spread. That low of 50 equals the record low. In 1962 the high was a cool 71 with a low of 54, a cool day.

More recently, there were large spreads of 30 degrees in both 1979 (88/58) and 1994 (82/52).

On the cool side, in 1981 the high was 74 with a low of 51. Three years later, in 1984, the high was 79 with the record low of 50. Another cool low was 52 in 1994. Two other cool highs were 73 in 1992 and 74 in 1997. The record coolest high of 63 occurred way back in 1892. The official thermometer was located near Lake Michigan at the time. 19 of the last 32 lows (59%) were in the 60s. Eight lows (25%) were in the cool 50s. Our most recent 50s low was 54 in 2003. Five lows (16%) were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:11 and sunrise is at 5:43. Sunset is at 20:16 and twilight ends at 20:48. There's a total of 14 hours, 33 minutes of daylight today and 15 hours, 37 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:12 and sunrise is at 5:44. The moon is waning crescent, heading towards new tomorrow at 13:40. Illumination was 3% at midnight, will be 1% at noon and 0% at midnight tonight. Although you won't be able to see it, moonrise is at 4:27 this morning. Moonset is at 19:24 tonight. Moonrise is at 5:38 tomorrow morning. Moonlight time is 14 hours, 57 minutes which is 25 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 38 days.