August 16: ORD

Today is August 16th. It's the 229th day of the year. 137 days remain. It's week 33 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 82 and the normal low is 63. I've calculated the 33-year averages at 83 and 62.

On the hot side, in 1988 (O'Hare's warmest August 16th) the high was the co-record high of 98 with a low of 73. Five years earlier, in 1983, the high was the other co-record high of 98 with a low of 71. In 1995 the high was 94 with a low of 73. The lows of 73 degrees (1988, 1995 and 2003) are O'Hare's warmest of the date. The record warmest low of 78 occurred back in 1913, at a time when the official readings were taken adjacent to Lake Michigan. 25 of the past 33 highs (76%) were in the: 70s (9) and 80s (16). O'Hare recorded consecutive 70s & 80s highs as follows: six from 1989 through 1994 and eight from 2004 through last year, 2011. Seven highs (21%) were in the hot 90s. Our most recent 90s high was 92 degrees in 2003. One high (3%) was in the cool 60s (66 in 1980). O'Hare also had a hot high of 94 degrees in 1968.

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1976 the low was a cold 49 degrees, just above the record low. In 1968 the high was a hot 94 degrees. In 1964 the high was 83 with a cold low of 46, a 37 degree spread. That low of 46 was colder than the record low. In 1963 the high was 81 with a cold low of 51, a 30 degree spread.

More recently, there was a large spread of 30 degrees in 2004 (78/48) and a small spread of five degrees in 2001 (70/65).
 
On the cool side, in 1979 (O'Hare's coolest August 16th) the high was 72 with a low of 45, a low colder than the record low and O'Hare's coldest low of the date. In 1992 the high was 74 with a low of 50. In 1980 the high was 66 (O'Hare's only 60s high of the date and just a degree above the record coolest high) with a low of 58. The official record low of 48 degrees was set in 2004. The former record low of 49 was set at Midway in 1976. The other cool highs were 70 degrees in 1981 and two decades later in 2001. The record coolest high of 65 occurred way back in 1902, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 50s (9) and 60s (17). O'Hare recorded consecutive 50s & 60s lows as follows: six from 1989 through 1994 and seven from 1996 through 2002. Two lows (6%) were in the cold 40s. Five lows (15%) were in the warm 70s. O'Hare's second coldest low (colder than the record low) of 46 degrees was posted in 1964. The low was 49 degrees at O'Hare (and Midway) in 1976, just above the record low.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:32 and sunrise is at 6:02. Sunset is at 19:52 and twilight ends at 20:22. There's a total of 13 hours, 50 minutes of daylight today and 14 hours, 50 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:33 and sunrise is at 6:03. The moon is waning crescent and will be new tomorrow at 10:54. Illumination was 2% at midnight, will be 1% at noon and 0% at midnight tonight. Moonrise was at 5:02 this morning. Moonset is at 19:00 tonight. Moonrise is at 6:08 tomorrow morning. Moonlight time is 13 hours, 58 minutes which is 31 minutes shorter 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 18 days.