August 9: ORD

Today is August 9th. It's the 222nd day of the year. 144 days remain. It's week 32 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 83 and the normal low is 64. I've calculated the 33-year averages at 84 and 64.

On the hot side, three years ago, in 2009 (O'Hare's warmest August 9th) the high was 91 with a low of 77 (O'Hare's warmest low of the date). In 2001 (O'Hare's second warmest August 9th) the high was 95 with a low of 72. The other hot high of 95 occurred in 2005. Those highs of 95 in 2001 and 2005 are O'Hare's hottest for the date. The second hottest highs of the date are 93 degrees in 1971, 1984 and 1992. The record high of 97 and record warmest low of 79 were set on the same hot day back in 1913, at a time when the official readings were taken adjacent to Lake Michigan. 17 of the past 33 highs (52%) were in the 80s. Eight highs (24%) were in the hot 90s. Eight highs (24%) were in the cool: 60s (1) and 70s (7). Our most recent 70s high was 77 in 2003. O'Hare's third warmest August 9th was in 1971 as the high was 93 with a low of 73.

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1976 the high was 83 with a cold low of 51, a 32 degree spread. That low of 51 equals the record low. In 1972 the low was a cold 51 degrees, equal to the record low of 51 set at Midway. In 1966 the low was a cool 52 degrees. In 1964 the high was 70 with a low of 45, a cool day. That low of 45 was also colder than the record low. The high on the 7th in 1964 was 92. That's a big 47 degree drop to the 45 degree low (in 1964).

More recently, there were large spreads of 34 degrees in 1985 (90/56) and 30 degrees in 2005 (95/65). The small spread was seven degrees in 1983 (79/72).
 
On the cool side, in 1994 the high was a cool 66 (O'Hare's only 60s high and coolest high of the date) with a low of 53. In 1982 the high was 74 with a low of 56. In 1999 the high was 77 with a low of 54. The record low of 51 was set in 1972 at Midway. The record coolest high of 64 was set way back in 1884, at a time when the official readings were taken adjacent to Lake Michigan. 17 of the last 33 lows (52%) were in the 60s. Nine lows (27%) were in the cool 50s. Our most recent 50s low was 57 in 2002. Seven lows (21%) were in the warm 70s. O'Hare's coolest August 9th was in 1964 as the high was 70 (O'Hare's second coolest high of the date) with a low of 45 (O'Hare's coldest low of the date and colder than the official record low). O'Hare also had cold lows of 51 degrees (tied with the record low) in 1972 and 1976. Additionally, the low was a cold 52 degrees in 1966.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:24 and sunrise is at 5:55. Sunset is at 20:02 and twilight ends at 20:32. There's a total of 14 hours, 7 minutes of daylight today and 15 hours, 8 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:25 and sunrise is at 5:56. The moon reaches last quarter today at 13:55. Illumination was 55% at midnight, will be 50% at noon and 46% at midnight tonight. Moonset is at 13:47 this afternoon. Moonrise is at 23:43 tonight. Moonset is at 14:43 tomorrow afternoon. Moonlight time is 14 hours, 4 minutes which is 23 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. Labor Day is in 25 days.