August 3: ORD

Today is August 3rd. It's the 216th day of the year. 150 days remain. It's week 31 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 86 and 64.

On the hot side, in 1988 (O'Hare's warmest August 3rd) the high was 96 with the record warmest low of 80. In 2005 the high was 93 with a low of 74. In 1987 the high was 96 with a low of 70. The other hot highs were 96 in 1983, 96 in 1964 and 95 in 1982. The four highs of 96 are O'Hare's hottest of the date. The record high of 98 was last set in 1964 at Midway, having been set previously in 1930 (University of Chicago) and 1944 (Midway). 19 of the past 33 highs (58%) were in the 80s. Ten highs (30%) were in the hot 90s. Four highs (12%) were in the cool 70s. From 1979-2011, this is the average tenth hottest day of the year. O'Hare's second warmest August 3rd was in 1964 as the high was 96 (tied with three others as hottest for the date) with a low of 76 (O'Hare's 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 1976 the high was 80 with a cold low of 49, a 31 degree spread. In 1972 the high was a cool 71 degrees. In 1966 the high was 77 with a cold low of 48, a cool day. That low of 48 equals the record low. In 1965 the high was 75 with a cool low of 50, a cool day. In 1964 the high was 96 with a low of 76, a hot day and year of the record high of 98 at Midway.

More recently, there were additional large spreads of 34 degrees in 1983 (96/62), 32 degrees in 1994 (88/56) and 31 degrees in 2002 (90/59). There was a small spread of seven degrees in 1995 (78/71).
 
On the cool side, in 2000 (O'Hare's second coolest August 3rd by just half a degree) the high was 72 (O'Hare's second coolest high of the date) with a low of 54. In 1985 the high was 81 with a low of 50, a 31 degree spread. In 1992 the high was 76 with a low of 56. The record low of 48 and record coolest high of 62 occurred on the same cool day way back in 1894, at a time when the official readings were taken adjacent to Lake Michigan. 18 of the last 33 lows (55%) were in the 60s. O'Hare recorded six consecutive 60s lows from 1979 through 1984. Eight lows (24%) were in the cold 50s, most recently 59 in 2002. Seven lows (21%) were in the warm: 70s (6) and 80s (1). O'Hare's coolest August 3rd days were in 1965 (high of 75, low of 50) and 1966 (high of 77, low of 48). That low of 48 degrees in 1966 is O'Hare's coldest reading of the date. The second coldest  low was 49 degrees in 1976. O'Hare's third coolest August 3rd was in 1972 as the high was 71 (O'Hare's coolest high of the date) with a low of 56.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:17 and sunrise is at 5:49. Sunset is at 20:10 and twilight ends at 20:41. There's a total of 14 hours, 21 minutes of daylight today and 15 hours, 24 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:18 and sunrise is at 5:50. The moon is waning gibbous, having reached the full Sturgeon (a.k.a. Green Corn) moon two nights ago at 22:27. Illumination was 98% at midnight, will be 97% at noon and 95% at midnight tonight. Moonset was at 7:35 this morning. Moonrise is at 20:44 tonight. Moonset is at 8:42 tomorrow morning. Moonlight time is 10 hours, 51 minutes which is 38 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 31 days.