August 5: ORD

Today is August 5th. It's the 218th day of the year. 148 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 81 and 64.

On the hot side, in 1996 (O'Hare's warmest August 5th) the high was 90 with a low of 73 (O'Hare's warmest low of the date). In 1980 the high was 87 with a low of 70. O'Hare's hottest highs of the date were 91 degrees in: 1965, 1968 and 1984. The record high of 102 was set back in 1918. The record warmest low of 78 was set way back in 1881. For both records, the official readings were taken adjacent to Lake Michigan. 20 of the past 33 highs (61%) were in the 80s. Two highs (6%) were in the hot 90s. 11 highs (33%) were in the cool: 60s (1) and 70s (10). Long stretches of highs under 90 characterize this day. For 11 years from 1985 through 1995 there were no 90s. For 15 years, still ongoing, from 1997 through 2011, there were no 90s. O'Hare's second warmest August 5th was in 1968 as the high was 91 with a low of 69.

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1978 the low was a cool 50 degrees, a reading colder than the record low. In 1974 and 1972 the lows were 51, equal to the record low. In 1966 the high was 82 with a cool low of 52, a 30 degree spread. In 1962 the high was 85 with a low of 54, a 31 degree spread.

More recently, there were no large spreads of at least 30 degrees or small spreads of up to seven degrees. 

On the cool side, in 1994 (O'Hare's coolest August 5th) the high was 68 (O'Hare's coolest high and only 60s high of the date) with the record low of 51. Three years later, in 1997, the high was 73 with a low of 53. Five years before that, in 1992, the high was also 73 with a low of 53. The other cold low, post-1978, was 52 in 1993. The record coolest high of 63 was set back in 1915, 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 consecutive 60s lows as follows: 11 from 1981 through 1991 and seven from 2005 through last year, 2011. 18 of the 24 lows in the 60s (75% of them) occurred during these two streaks. Six lows (18%) were in the cold 50s. Our most recent 50s low was 58 in 2004. Three lows (9%) were in the warm 70s. Our most recent 70s low was 71 in 1998. O'Hare's coldest low was 50 degrees in 1978, a low colder than the official record low. 1972 and 1974 registered lows of 51 degrees, equal to the record low. The other cold low, pre-1979, was 52 degrees in 1966.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:20 and sunrise is at 5:51. Sunset is at 20:07 and twilight ends at 20:38. There's a total of 14 hours, 16 minutes of daylight today and 15 hours, 18 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:21 and sunrise is at 5:52. The moon is waning gibbous. Illumination was 89% at midnight, will be 85% at noon and 82% at midnight tonight. Moonset was at 9:46 this morning. Moonrise is at 21:39 tonight. Moonset is at 10:48 tomorrow morning. Moonlight time is 12 hours, 7 minutes which is 37 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 29 days.