July 10, 2012

Today is July 10th. It's the 192nd day of the year. 174 days remain. It's week 28 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. Before this, the official site of record was on the south side of Chicago at Midway International Airport (MDW), beginning on Wednesday, July 1, 1942. From Friday, January 1, 1926 through Tuesday, June 30, 1942, the official site was at the University of Chicago. Before that, the official site was at various locations in Chicago going back to Monday, October 16, 1871. Observations taken from October 15, 1870 to October 8, 1871 were lost in the Great Chicago Fire.

According to the National Climatic Data Center (NCDC), the normal high is 85 and the normal low is 64. I've calculated the 33-year averages at 85 and 63.

On the hot side, in 1989 (O'Hare's warmest July 10th) the high was 101 (a degree off the record) with a low of 73. Five years earlier, in 1984, the high was 99 with a low of 66, a 33 degree spread. Last year, in 2011, the high was 91 with a low of 74. The record high of 102 and record warmest low of 80 were set on the same hot day back in 1936 at the University of Chicago. The record high of 102 was originally set way back in 1901. 15 of the past 33 highs (46%) were in the 80s. Ten highs (30%) were in the hot: 90s (9) and 100s (1). Eight highs (24%) were in the cool 70s. O'Hare's second warmest July 10th was in 1976 as the high was 97 with a low of 76 (O'Hare's warmest low of the date). O'Hare also had a hot high of 97 in 1966.

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1976 the high was 97 with a low of 76, a hot day. In 1968 the high was a cool 67 with a low of 53, a cool day. In 1966 the high was a hot 97 degrees. In 1965 the high was 80 with a cold low of 50 (equal to the record), a 30 degree spread. In 1963 the high was 83 with a cold low of 45 (lower than the record), a 38 degree spread. In 1962 the high was 84 with a cold low of 51 (just above the record), a 33 degree spread. In 1960 the high was a cool 72 degrees.

More recently, there were large spreads of 35 degrees in 1981 (91/56) and 31 degrees in 2005 (91/60).

On the cool side, in 1996 the high was 75 with the co-record low of 50. Three years later, in 1999, the high was 74 with a low of 54. Two years prior, in 1997, the high was 78 with the co-record low of 50. Another cool high was 73 degrees in 2006. The record coolest high of 62 occurred back in 1917, at a time when the official readings were taken adjacent to Lake Michigan. 24 of the last 33 lows (73%) were in the 60s. O'Hare recorded 11 consecutive 60s lows from 2000 through 2010. Seven lows (21%) were in the cold 50s. Two lows (6%) were in the warm 70s. Our most recent 50s low was 54 in 1999. O'Hare's coolest July 10th was in 1968 as the high was 67 (O'Hare's coolest high of the date) with a low of 53. O'Hare's coldest low of the date was 45 degrees in 1963.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:53 and sunrise is at 5:27. Sunset is at 20:30 and twilight ends at 21:04. There's a total of 15 hours, 3 minutes of daylight today and 16 hours, 11 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 4:54 and sunrise is at 5:28. The moon reaches last quarter tonight at 20:48. Illumination was 58% at midnight, will be 53% at noon and 48% at midnight tonight. Moonset is at 13:02 this afternoon. Moonrise is at 0:05 tomorrow morning. Moonset is at 14:02 tomorrow afternoon. Moonlight time is 13 hours, 2 minutes which is 38 minutes longer than yesterday.

Summer began on June 4th and runs for 110 days through September 21st. High temperatures in this period are usually in the 70s and 80s. Highs in the 90s and 100s occur infrequently. Parent's Day is in 12 days.