July 23: ORD

Today is July 23rd. It's the 204th day of the year. 161 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 82 and 63.

On the hot side, in 2001 the high was 92 with a low of 73. Two years prior, in 1999, the high was 94 with a low of 71. The other 90s highs were 94 in 1979, 94 last year (in 2010) and 92 in 1987. The record high of 99 was set way back in 1914. The warm lows were 74 in 1984 and 73 in both 1983 and 2001. The record warmest low of 78 occurred in 1965. 26 of the past 32 highs (81%) were in the: 70s (9) and 80s (17). Five highs were in the hot 90s. One high was in the cool 60s.

In looking back through the years to the first July at O'Hare in 1959, the following instance was notable: In 1972 the low was a warm 77 degrees.

More recently, there were no other large or small daily temperature spreads.

On the cool side, in 1992 the high was the record coolest high (and only 60s high) of 64 with a low of 60, a small four degree spread. In 2000 the high was 73 with a low of 52. The high was just 73 in 2004 as well. The record low of 51 was set in 1947. 19 of the last 32 lows (59%) were in the 60s. Seven lows (22%) were in the cool 50s. Six lows (19%) were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:04 and sunrise is at 5:37. Sunset is at 20:22 and twilight ends at 20:55. There's a total of 14 hours, 45 minutes of daylight today and 15 hours, 51 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:05 and sunrise is at 5:38. The moon reaches last quarter today at 0:02. Illumination was 50% at midnight, will be 45% at noon and 40% at midnight tonight. Moonset is at 14:08 this afternoon. Moonrise is at 0:10 tomorrow. Moonset is at 15:08 tomorrow afternoon. Moonlight time is 14 hours, 8 minutes which is 39 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. Parent's Day is tomorrow.