August 6: ORD

Today is August 6th. It's the 219th day of the year. 147 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 83 and 64.

On the hot side, in 1984 (O'Hare's second warmest August 6th) the high was 94 (O'Hare's second hottest high of the date) with a low of 71. In 2001 the high was 92 with a low of 70. In 2007 the high was 88 with a low of 74 (O'Hare's second warmest low of the date). The record high of 101 was last reached in 1947 at Midway after originally being set back in 1918. The record warmest low of 82 was set back in 1918. In 1918 the official readings were taken adjacent to Lake Michigan. 20 of the past 33 highs (61%) were in the 80s. O'Hare recorded seven consecutive 80s highs from 2005 through last year, 2011. Four highs (12%) were in the hot 90s. Nine highs (27%) were in the cool 70s. Our most recent 70s high was 76 in 2004. O'Hare's warmest August 6th was in 1968 as the high was 96 (O'Hare's hottest high of the date) with a low of 77 (O'Hare's warmest low of the date). 

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1968 the high was 96 with a low of 77, a hot day. In 1964 the high was 85 with a low of 54, a 31 degree spread.

More recently, there were large spreads of 35 degrees in 1988 (93/58) and 30 degrees in 1987 (87/57).
 
On the cool side, in 1994 (O'Hare's coolest August 6th) the high was 72 with the record low (and only 40s low) of 48. Four years earlier, in 1990, the high was 70 (O'Hare's coolest high of the date) with a low of 54. The year before, in 1989, the high was 72 with a low of 53. The record coolest high of 65 was set way back in 1893, at a time when the official readings were taken adjacent to Lake Michigan. 25 of the last 33 lows (76%) were in the: 50s (9) and 60s (16). O'Hare recorded nine consecutive 50s & 60s lows from 1985 through 1993. Our most recent 50s lows were 54 in 2004 and 59 in 2005. One low (3%) was in the cold 40s (the record low of 48 in 1994). Seven lows (21%) were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:21 and sunrise is at 5:52. Sunset is at 20:06 and twilight ends at 20:37. There's a total of 14 hours, 14 minutes of daylight today and 15 hours, 16 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:22 and sunrise is at 5:53. The moon is waning gibbous. Illumination was 82% at midnight, will be 78% at noon and 74% at midnight tonight. Moonset is at 10:48 this morning. Moonrise is at 22:07 tonight. Moonset is at 11:49 tomorrow morning. Moonlight time is 12 hours, 41 minutes which is 34 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 28 days.