July 7: ORD

Today is July 7th. It's the 189th day of the year. 177 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. 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 84 and the normal low is 64. I've calculated the 33-year averages at 85 and 62.

On the hot side, in 1988 (O'Hare's warmest July 7th) the high was 97 with a low of 71. Two years ago, in 2010 (O'Hare's second warmest July 7th), the high was 93 with a low of 71. The record high of 102 degrees was set in 1980. Our warmest low was 73 in 1994. The record warmest low of 78 occurred way back in 1876, at a time when the official readings were taken adjacent to Lake Michigan. 16 of the past 33 highs (49%) were in the 80s. Eight highs (24%) were in the hot: 90s (7) and 100s (1). Nine highs (27%) were in the cool: 60s (1) and 70s (8). 

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1969 the high was a cool 65 with a low of 60, a five degree spread and cool day. In 1967 the low was a cold 51 degrees. In 1961 the high was a cool 70 with a low of 53, a cool day. In 1959 the high was 87 with a low of 56, a 31 degree spread.

More recently, there were large spreads of: 43 degrees in 1980 (102/59), 36 degrees in 1981 (93/57), 30 degrees in 1979 (85/55) and 30 degrees in 1985 (88/58).

On the cool side, in 1984 (O'Hare's coolest July 7th) the high was 74 with a low of 47. The year earlier, 1983 (O'Hare's third coolest July 7th), the high was 79 with the record low of 45. The only post-1979 cool high was 69 in 2004. The record coolest high of 62 occurred back in 1904, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 50s (10) and 60s (16). O'Hare recorded 13 consecutive 50s & 60s lows from 1995 through 2007. 10 of these 13 (77%) were in the 60s. Two lows (6%) were in the cold 40s (45 in 1983 & 47 in 1984). Five lows (15%) were in the warm 70s. O'Hare's second coolest July 7th was in 1961 as the high was 70 with a low of 53. O'Hare's fourth coolest July 7th was in 1969 as the high was 65 (O'Hare's coolest high of the date) with a low of 60.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:51 and sunrise is at 5:25. Sunset is at 20:32 and twilight ends at 21:06. There's a total of 15 hours, 7 minutes of daylight today and 16 hours, 15 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 4:51 and sunrise is at 5:25. The moon is waning gibbous. Illumination was 85% at midnight, will be 81% at noon and 77% at midnight tonight. Moonset is at 9:55 this morning. Moonrise is at 22:44 tonight. Moonset is at 10:59 tomorrow morning. Moonlight time is 11 hours, 11 minutes which is 39 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 15 days.