July 4: ORD

Today is July 4th. It's the 185th day of the year. 180 days remain. It's week 27 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 62. I've calculated the 32-year averages at 84 and 64.

On the hot side, in 1990 the high was 96 with a low of 77. In 1999 the high was 93 with a low of 79. In 2003 the high was 94 with a low of 73. The other 90s highs were 91 in 1985, 91 in 1994, 91 last year (in 2010) and 90 in 2002. The other warm lows were 75 in 1993 and 74 in 1994. The record high of 102 was set back in 1911. The record warmest low of 80 occurred back in 1921. 16 of the past 32 highs (50%) were in the 80s. Seven highs (22%) were in the hot 90s. Nine highs (28%) were in the cool: 60s (2) and 70s (7).

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1977 the high was 95 with a low of 78, a hot day. In 1972 the high was 66 with a low of 49 (cooler than the record low), a cool day. 1972 was also the year of the record low of 50 at Midway. In 1967 the high was 64 with a low of 50 (tied with the record low), a cool day. In 1964 the low was a cool 50 degrees (tied with the record low). In 1963 the high was 79 with a cool low of 46 (cooler than the record low), a 33 degree spread. In 1961 the high was a cool 65 with a low of 60, a five degree spread.

More recently, there were large spreads of 33 degrees in 1988 (89/56) and 30 degrees in 1985 (91/61).

On the cool side, in 1997 the high was 66 with a low of 56. Two years ago, in 2009, the high was 69 with a low of 59. Three years ago, in 2008, the high was 76 with a low of 52. In 1996 the high was 77 with a low of 51. In 1979 the high was 74 with a low of 54. The record low of 50 was set in 1972 at Midway. The record coolest high of 62 occurred back in 1920. 17 of the last 32 lows (53%) were in the 60s. Nine lows (28%) were in the cool 50s. Six lows (19%) were in the warm 70s. Our most recent 70s low was 70 in 2004.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:48 and sunrise is at 5:22. Sunset is at 20:33 and twilight ends at 21:07. There's a total of 15 hours, 11 minutes of daylight today and 16 hours, 19 minutes between twilights. We lost no minutes of daylight from yesterday. Tomorrow twilight begins at 4:49 and sunrise is at 5:23. The moon is waxing crescent. Illumination was 10% at midnight, will be 14% at noon and 18% at midnight tonight. Moonrise is at 9:08 this morning. Moonset is at 22:31 tonight. Moonrise is at 10:20 tomorrow morning. Moonlight time is 13 hours, 23 minutes which is 42 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. Independence Day is today. Parent's Day is in 20 days.