August 1: ORD

Today is August 1st. It's the 214th day of the year. 152 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 65.

On the hot side, in 2006 (O'Hare's warmest August 1st) the high was 99 with the record warmest low of 80. In 1988 (O'Hare's second warmest August 1st) the high was the record high of 100 with the former record warmest low of 78. In 1987 (O'Hare's third warmest August 1st) the high was 97 with a low of 77. The other hot high was 95 in 1991. The other warm low was 76 in 2001. 26 of the past 33 highs (79%) were in the: 80s (17) and 90s (9). O'Hare recorded 12 consecutive 80s & 90s highs from 1997 through 2008. One high (3%) was in the hot 100s. Six highs (18%) were in the cool 70s. An interesting side bar is that for nine years in a row, from 1992 to 2000, there were no highs in the 90s. From 1979-2011, this is the average fifth hottest day of the year.

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1974 the high was a cool 67 with a low of 62, a five degree spread. In 1973 the high was a cool 70 degrees. In 1965 the high was a cool 69 with a low of 54, a cool day. In 1961 the high was 77 with a low of 71, a six degree spread.

More recently, there was a large spread of 32 degrees in 1991 (95/63).

On the cool side, in 1990 (O'Hare's second coolest August 1st) the high was 76 with the record low of 51. The former record low was 52 in 1947. In 1985 the high was 75 with a low of 54. In 1979 the high was 70 with a low of 60. The record coolest high of 66 occurred way back in 1875, at a time when the  official readings were taken adjacent to Lake Michigan. 20 of the last 33 lows (61%) were in the 60s. Six lows (18%) were in the cold 50s. Our most recent 50s low was 58 in 1998. Seven lows (21%) were in the warm: 70s (6) and 80s (1). O'Hare's coolest August 1st was in 1965 as the high was 69 with a low of 54. O'Hare's coolest high of 67 degrees occurred in 1974.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:15 and sunrise is at 5:47. Sunset is at 20:12 and twilight ends at 20:43. There's a total of 14 hours, 25 minutes of daylight today and 15 hours, 28 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:16 and sunrise is at 5:48. The moon reaches the full Sturgeon (a.k.a. Green Corn) moon tonight at 22:27. Illumination was 99% at midnight, will be 100% at noon and 100% at midnight tonight. Moonset was at 5:16 this morning. Moonrise is at 19:40 tonight. Moonset is at 6:27 tomorrow morning. Moonlight time is 9 hours, 36 minutes which is 32 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 33 days.