August 30: ORD

Today is August 30th. It's the 243rd day of the year. 123 days remain. It's week 35 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 80 and the normal low is 61. I've calculated the 33-year averages at 80 and 61.

On the hot side, in 1995 (O'Hare's warmest August 30th) the high was 92 (O'Hare's co-hottest high) with a low of 74. Two years ago, in 2010 (O'Hare's second warmest August 30th), the high was 88 with a low of 74. Since our only other 90s high of 90 degrees occurred in 1993, the 90s highs occurred within two years of each other! Those lows of 74 degrees are O'Hare's warmest of the date. The record high of 96 degrees was last set in 1953 at Midway after originally being set back in 1925 adjacent to Lake Michigan. The record warmest low of 76 degrees occurred in 1932 at the University of Chicago, having originally been set way back in 1881 adjacent to Lake Michigan. 28 of the past 33 highs (85%) were in the: 70s (12) and 80s (16). Two highs were in the hot 90s. Three highs were in the cool 60s. There were two long streaks of highs in the 70s & 80s. The first was 22 years from 1971 through 1992 and then nine years from 2000 through 2008. O'Hare's third warmest August 30th was in 1969 as the high was 90 with a low of 71. The other co-hottest high of 92 degrees occurred in 1962. O'Hare's 91 degree highs occurred in 1961 and 1970.

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 79 with a low of 49, a 30 degree spread. In 1967 the high was a cool 67 degrees. In 1965 the high was a cool 64 degrees. In 1962 the high was a hot 92 with a low of 62, a 30 degree spread. In 1959 the temperatures for yesterday (the 29th) and today (the 30th) were the same: a high of 86 with a low of 69.
More recently, there was a large spread of 31 degrees in 2008 (87/51) and a small spread of six degrees in 1994 (67/61).
 
On the cool side, three years ago, in 2009 (O'Hare's coolest August 30th), the high was 66 with a low of 51. In 1999 the high was 69 with a low of 55. The only other post-1978 60s high was 67 degrees in 1994. In 1986 the high was 76 with a low of 48 (O'Hare's coldest low of the date). The other 40s lows were 49 degrees in 1976 and 1988 (O'Hare's second coldest lows of the date). So post-1978, the 40s lows occurred within two years of each other! The record low of 47 degrees was last set in 1946 at Midway after originally being set back in 1915 adjacent to Lake Michigan. The record coolest high of 58 degrees occurred back in 1915, at a time when the official readings were taken adjacent to Lake Michigan. 25 of the last 33 lows (76%) were in the: 50s (13) and 60s (12). Two lows (6%) were in the cold 40s. Six lows (18%) were in the warm 70s. For nine straight years, from 2001 through 2009, lows were in the 50s & 60s. O'Hare's second coolest August 30th was in 1965 as the high was 64 (O'Hare's coolest high of the date) with a low of 54.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:48 and sunrise is at 6:17. Sunset is at 19:30 and twilight ends at 19:59. There's a total of 13 hours, 13 minutes of daylight today and 14 hours, 11 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:49 and sunrise is at 6:18. The moon is waxing gibbous and will be full tomorrow as the Corn (a.k.a. Green Corn or Grain) moon at 8:58. Since this is also the second full moon of the month, it's also Blue moon. Illumination was 98% at midnight, will be 99% at noon and 100% at midnight tonight. Moonset was at 5:19 this morning. Moonrise is at 18:43 tonight. Moonset is at 6:25 tomorrow morning. Moonlight time is 10 hours, 36 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 four days.