July 6: ORD

Today is July 6th. It's the 188th day of the year. 178 days remain. It's week 27 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 63. I've calculated the 33-year averages at 85 and 62.

On the hot side, in 1994 the high was 94 with a low of 72. In 1988 the high was the record high of 99 with a low of 66, a 33 degree spread. The record high of 99 was originally set way back in 1874. The other hot high was 96 in 1991 (tied with 1977 as O'Hare's second hottest high of the date). The record warmest low of 80 occurred in 1977 at Midway. 17 of the past 33 highs (52%) were in the 80s. O'Hare recorded ten consecutive 80s highs from 1996 through 2005. Eight highs (24%) were in the hot 90s. Eight highs (24%) were in the cool: 60s (1) and 70s (7). Five of the eight highs in the 90s occurred from 1986 to 1991. O'Hare's warmest July 6th was in 1977 as the high was 96 (with 1991, tied as O'Hare's second hottest high of the date) and O'Hare's warmest low of the date of 78.

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 96 with a low of 78, a hot day and year of the record warmest low (80 at Midway). In 1969 the high was a cool 65 with a low of 61, a four degree spread. In 1968 the high was 81 with a cold low of 49, a 32 degree spread. In 1967 the high was 76 with a cold low of 46 (tied with the record), a 30 degree spread. In 1965 the high was 80 with a cold low of 42 (colder than the record), a 38 degree spread. In 1964 the high was a cool 72 degrees. In 1961 the high was 78 with a cold low of 48, a 30 degree spread. In 1959 the high was a cool 72 degrees.

More recently, there were additional large spreads of: 33 degrees in 1989 (95/62), 31 degrees in 2001 (81/50), 30 degrees in 1981 (88/58) and 30 degrees in 1996 (88/58).

On the cool side, in 1983 (O'Hare's coolest July 6th) the high was 71 with the co-record low of 46. Four years earlier, in 1979, the high was 78 with a low of 43. That low of 43 was colder than the record low and is O'Hare's second coldest low of the date. These 40s lows were the only ones since 1979. In 1984 the high was 74 with a low of 50. The other co-record low of 46 was set at Midway in 1979. The other cold lows were 50 in 2001 and 51 in 1992. The other cool high was 69 in 1990, O'Hare's coolest high of July 6th. The record coolest high of 63 occurred way back in 1873, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 50s (11) and 60s (15). There were consecutive lows in the 50s & 60s as follows: ten from 1984 through 1993 and ten from 2000 through 2009. 77% (20 of 26) of the 50s & 60s lows occurred in these two streaks. Two lows (6%) were in the cold 40s and five (15%) were in the warm 70s. O'Hare's coldest low of the date is 42 degrees in 1965, a low colder than the record low.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:50 and sunrise is at 5:24. Sunset is at 20:32 and twilight ends at 21:06. There's a total of 15 hours, 8 minutes of daylight today and 16 hours, 16 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 4:51 and sunrise is at 5:25. The moon is waning gibbous, having reached the full Buck moon three days ago at 13:52. Illumination was 92% at midnight, will be 89% at noon and 85% at midnight tonight. Moonset is at 8:48 this morning. Moonrise is at 22:16 tonight. Moonset is at 9:55 tomorrow morning. Moonlight time is 10 hours, 32 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. Parent's Day is in 16 days.