July 30: ORD

Today is July 30th. It's the 211th day of the year. 154 days remain. It's week 31 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 83 and the normal low is 64. I've calculated the 32-year averages at 83 and 64.

On the hot side, in 1999 the high was 101 (a degree short of the record) with a low of 78. In 2006 the high was 90 (our most recent 90s high) with a low of 77. In 1995 the high was 96 with a low of 70. In 1988 the high was 95 with a low of 70. The record high of 102 and record warmest low of 84 were set on the same hot day back in 1916. Our other 70s lows were 72 in 2008 (our most recent) and 70 in 2001. We had very high dew points in 1999. The top was 83 degrees, making 1999 perhaps the most humid July 30 on record. The dew point was at or above 80 degrees for 18 hours in 1999. 22 of the past 32 highs (69%) were in the: 70s (10) and 80s (12). Eight highs (25%) were in the hot: 90s (7) and 100s (1). Two highs (6%) were in the cool 60s. An interesting phenomenon is the drop in high temperature in the year following at minimum a 95 degree high. The three examples so far: 1988 (95) followed by 1989 (75), 20 degrees cooler; 1995 (96) followed by 1996 (75), 21 degrees cooler; 1999 (101) followed by 2000 (74), 27 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 high was 72 with a low of 53, a cool day. In 1965 the high was 82 with a cool low of 50, a 32 degree spread. That low of 50 is equal to the record low.

More recently, there were large spreads of 32 degrees in 1984 (82/50) and 31 degrees in 2003 (84/53). There were small spreads of five degrees in 1985 (69/64) and six degrees in 2000 (74/68).

On the cool side, in 1992 the high was 65 with a low of 58, a seven degree spread. In 1981 the high was 76 with a low of 53. The record low of 50 was set in 1984. Other cool highs were 69 in 1985 and 72 in 2004. The record coolest high of 62 occurred way back in 1895. The official thermometer was located near Lake Michigan at the time. 26 of the last 32 lows (81%) were in the: 50s (11) and 60s (15). Six lows were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:12 and sunrise is at 5:44. Sunset is at 20:15 and twilight ends at 20:47. There's a total of 14 hours, 31 minutes of daylight today and 15 hours, 35 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:13 and sunrise is at 5:45. The moon is new today at 13:40. Illumination was 0% at midnight, will be 0% at noon and 0% at midnight tonight. Although you won't be able to see it, moonrise is at 5:38 this morning. Moonset is at 20:00 tonight. Moonrise is at 6:51 tomorrow morning. Moonlight time is 14 hours, 22 minutes which is 35 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 37 days.