August 26: ORD

Today is August 26th. It's the 239th day of the year. 127 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 62. I've calculated the 33-year averages at 82 and 63.

On the hot side, in 1993 (O'Hare's co-warmest August 26th) the high was 94 with a low of 74 (O'Hare's co-second warmest low of the date). A decade later, in 2003, the high was 92 (our most recent 90s high) with a low of 71. In 1980 the high was 92 with a low of 69. In 1995 the high was 91 with a low of 69. The high of  93 degrees in 1991 is O'Hare's co-second hottest high of the date. The record high of 97 and record warmest low of 77 were set on the same hot day in 1973 at Midway. The record high of 97 was originally set two decades earlier in 1953. 27 of the past 33 highs (82%) were in the: 70s (10) and 80s (17). Five highs were in the hot 90s. One high was in the cool 60s (65 in 1987). O'Hare's co-warmest August 26th was in 1973 as the high was 93 (O'Hare's other co-second hottest high) with a low of 75 (O'Hare's warmest low of the date). O'Hare's second warmest August 26th was in 1959 as the high was 92 with a low of 74 (O'Hare's other co-second 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 93 with a low of 75, a hot day. This was the year that the records were set at Midway Airport. In 1971 the high was a cool 68 degrees. In 1968 the high was a cool 65 with a low of 54, a cool day. In 1964 the high was 74 with a cold low of 41, a 33 degree spread and cool day. That low of 41 was colder than the record low. In 1963 the low was a cool 50 degrees. In 1959 the high was 92 with a warm low of 74, a hot day.

More recently, there were no small spreads of up to seven degrees or large spreads of at least 30 degrees.
 
On the cool side, in 1987 the high was 65 (O'Hare's co-coolest high of the date) with a low of 57. In the following year of 1988, the high was 77 with a low of 54. In 1992 the high was 72 with a low of 60. The record low of 47 was set way back in 1887. The record coolest high of 61 occurred way back in 1885. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 21 of the last 33 lows (64%) were in the 60s. O'Hare recorded six consecutive 60s lows from 2004 through 2009. Nine lows (27%) were in the cold 50s. Three lows (9%) were in the warm 70s. O'Hare's coolest August 26th was in 1964 as the high was 74 with a low of 41 (O'Hare's coldest low of the date, a low six degrees colder than the record low). O'Hare's second coolest August 26th was in 1968 as the high was 65 (O'Hare's other co-coolest high of the date) with a low of 54. O'Hare's second coldest low of 50 degrees occurred in 1963. O'Hare's second coolest high if the date is 68 degrees in 1971.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:44 and sunrise is at 6:13. Sunset is at 19:36 and twilight ends at 20:05. There's a total of 13 hours, 23 minutes of daylight today and 14 hours, 21 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:45 and sunrise is at 6:14. The moon is waxing gibbous, having reached first quarter two days ago at 8:54. Illumination was 69% at midnight, will be 74% at noon and 79% at midnight tonight. Moonset was at 0:50 this morning. Moonrise is at 16:10 this afternoon. Moonset is at 1:54 tomorrow morning.  Moonlight time is 8 hours, 40 minutes which is five minutes shorter than yesterday. Moonlight time is at its shortest today.

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 eight days.