July 19: ORD

Today is July 19th. It's the 201st day of the year. 165 days remain. It's week 29 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 84 and the normal low is 64. I've calculated the 33-year averages at 85 and 66.

On the hot side, in 1991 the high was 99 (O'Hare's hottest high of the date) with a low of 72. Last year, in 2011, the high was 93 with the new co-record warmest low of 78. 1991 and 2011 are tied as O'Hare's second warmest July 19ths. The other co-record warmest low of 78 degrees occurred in 1977 at Midway. O'Hare's third hottest high of 96 degrees occurred in 1983. The record high of 101 degrees was set back in 1930 at the University of Chicago. O'Hare's third warmest low of the date was 76 degrees in 1981. 21 of the past 33 highs (64%) were in the 80s. O'Hare recorded six consecutive 80s highs from 1992 through 1997. Seven highs (21%) were in the hot 90s. Five highs (15%) were in the cool: 60s (1) and 70s (4). O'Hare's warmest July 19th was in 1977 as the high was 97 (O'Hare's second hottest high of the date) with a low of 77 (O'Hare's second warmest low of the date). From 1979-2011, this is the average sixth hottest day of the year.

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1977 the high was 97 with a low of 77, a hot day. 1977 was also the year of the record warmest low of 78. In 1969 the high was 76 with a low of 69, a seven degree spread. In 1962 the high was 83 with a low of 53, a 30 degree spread.

More recently, there were large spreads of 30 degrees in 1984 (84/54) and 30 degrees in 2003 (83/53). The small spread was six degrees in 1989 (71/65).

On the cool side, in 2000 (O'Hare's coolest July 19th) the high was 69 (O'Hare's coolest and only 60s high) with a low of 56. Three years ago, in 2009, the high was 71 with a low of 57. O'Hare's coldest lows of the date were 53 degrees in 1962 and 2003. The record low of 50 degrees was set way back in 1873. The other cool high was 71 degrees in 1989. The record coolest high of 65 degrees occurred back in 1912. Both the record low and record coolest high occurred 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 cool 50s. Seven lows (21%) were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:01 and sunrise is at 5:34. Sunset is at 20:25 and twilight ends at 20:58. There's a total of 14 hours, 51 minutes of daylight today and 15 hours, 57 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 5:02 and sunrise is at 5:35. The moon is waxing crescent, having become new last night at 23:24. Illumination was 0% at midnight, will be 0% at noon and 1% at midnight tonight. Moonrise was at 6:11 this morning. Moonset is at 20:29 tonight. Moonrise is at 7:15 tomorrow morning. Moonlight time is 14 hours, 18 minutes which is 28 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. Parent's Day is in three days.