August 28: ORD

Today is August 28th. It's the 241st day of the year. 125 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 81 and the normal low is 61. I've calculated the 33-year averages at 81 and 62.

On the hot side, in 1991 (O'Hare's second warmest August 28th) the high was 95 with a low of 71. In 1980 the high was 95 with a low of 69. Those highs of 95 degrees are O'Hare's hottest of the date. The other hot highs were 94 degrees (O'Hare's second hottest high of the date) in 1984 and 93 degrees (O'Hare's third hottest high of the date) in 1990. The record high of 97 degrees was first set in 1953 and tied just two years later in 1955. The record warmest low of 77 degrees was set in 1973. These records were set at Midway. 29 of the past 33 highs (88%) were in the: 70s (13), 80s (8) and 90s (8). Four highs were in the cool 60s. O'Hare's warmest August 28th was in 1973 as the high was 92 with a low of 75 (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 1973 the high was 92 with a warm low of 75, a hot day and year of the record warmest low. In 1967 the high was 78 with a cold low of 47, a 31 degree spread. In 1965 the high was 65 with a low of 42, a cool day and year of the record coolest high. In 1962 the high was 89 with a low of 59, a 30 degree spread.

More recently, there was a large spread of 33 degrees in 2003 (high of 92, low of 59). There were no small spreads of seven degrees or less.
 
On the cool side, in 1986 (O'Hare's co-coolest August 28th) the high was 65 with the record low of 42. Four years earlier, in 1982, the high was 66 with a low of 43 (O'Hare's second coldest low of the date). The other cool highs were 68 degrees three years ago (in 2009) and 69 degrees in 1992. The record coolest high of 62 degrees occurred in 1965 at Midway. The former record coolest high of 63 degrees occurred way back in 1891. 21 of the last 33 lows (64%) were in the 60s. O'Hare recorded seven consecutive 60s lows from 2005 through last year, 2011. Ten lows (30%) were in the cool: 40s (2) and 50s (8). Our most recent 50s low was 59 degrees in 2004. Two lows (6%) were in the warm 70s. O'Hare's other co-coolest August 28th was in 1965 as the high was 65 with a low of 42 (tied with the record low). O'Hare's third coldest low is 47 degrees in 1967. 

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:46 and sunrise is at 6:15. Sunset is at 19:33 and twilight ends at 20:02. There's a total of 13 hours, 18 minutes of daylight today and 14 hours, 16 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:47 and sunrise is at 6:16. The moon is waxing gibbous, three days away from the full 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 referred to as the Blue moon. Illumination was 87% at midnight, will be 91% at noon and 94% at midnight tonight. Moonset was at 3:02 this morning. Moonrise is at 17:37 this afternoon. Moonset is at 4:11 tomorrow morning. Moonlight time is 9 hours, 25 minutes which is 28 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 six days.