July 9: ORD

Today is July 9th. It's the 191st day of the year. 175 days remain. It's week 28 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 85 and the normal low is 64. I've calculated the 33-year averages at 85 and 64.

On the hot side, in 1989 (O'Hare's warmest July 9th) the high was 97 with a low of 71. In the prior year of 1988 (tied with 1974 as O'Hare's second warmest July 9th), the high was also 97 but with a "cooler" low of 68. These highs of 97 are tied with the high of 97 in 1974 as O'Hare's hottest highs of the date. The record high of 98 was set at Midway in 1974. The record warmest low of 79 occurred way back in 1897, at a time when the official readings were taken adjacent to Lake Michigan. 25 of the past 33 highs (76%) were in the: 80s (15) and 90s (10). O'Hare recorded seven consecutive 80s & 90s highs from 1987 through 1993. Eight highs (24%) were in the cool: 60s (2) and 70s (6). 1974 was the warmest July 9th prior to 1988. In 1974 (tied with 1988 as O'Hare's second warmest July 9th) the high was 97 with a low of 68. O'Hare's warmest lows of the date were 72 degrees, occurring in 1973, 1990, 1993 and 2000.

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1974 the high was a hot 97 degrees (the low was 68). 1974 was the year of the record high of 98 at Midway. In 1963 the high was 72 with a low of 47 (colder than the record low), a cool day. In 1961 the high was 79 with a cold low of 49 (colder than the record low), a 30 degree spread.

More recently, there were large spreads of 33 degrees last year, in 2011 (91/61) and 32 degrees in 2005 (88/56).

On the cool side, in 1997 (O'Hare's second coolest July 9th) the high was 69 with a low of 53. The prior year of 1996 (O'Hare's third coolest July 9th) had a high also of 69 but with a slightly warmer low of 56. These highs of 69 are O'Hare's coolest highs of the date.  The record low of 50 and record coolest high of 63 occurred on the same cool day way back in 1895, at a time when the official readings were taken adjacent to Lake Michigan. 19 of the last 33 lows (58%) were in the 60s. Seven lows (21%) were in the cool 50s. Seven lows (21%) were in the warm 70s. O'Hare's coolest July 9th was in 1963 as the high was 72 with a low of 47 (O'Hare's coldest low of the date). O'Hare's second coldest low of the date was 49 in 1961.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:52 and sunrise is at 5:26. Sunset is at 20:31 and twilight ends at 21:05. There's a total of 15 hours, 5 minutes of daylight today and 16 hours, 13 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 4:53 and sunrise is at 5:27. The moon is waning gibbous and will reach last quarter tomorrow night at 20:48. Illumination was 68% at midnight, will be 63% at noon and 58% at midnight tonight. Moonset is at 12:01 this afternoon. Moonrise is at 23:37 tonight. Moonset is at 13:02 tomorrow afternoon. Moonlight time is 12 hours, 24 minutes which is 36 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 13 days.