July 12: ORD

Today is July 12th. It's the 194th day of the year. 172 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 84 and 64.

On the hot side, in 1995 (O'Hare's warmest July 12th) the high was the record high of 97 (also our most recent 90s high) with a low of 73. The record high of 97 originally occurred in 1952 and was tied in 1954. In 1981 (tied with 1966 as O'Hare's second warmest July 12th) the high was 94 with a low of 73. The record warmest low of 79 occurred back in 1921, at a time when the official readings were taken adjacent to Lake Michigan. 23 of the past 33 highs (70%) were in the 80s. There were two significant streaks of 80s highs. The first was six years from 1996 through 2001. The second was nine years from 2003 through last year, 2011. Six highs (18%) were in the hot 90s and four highs (12%) were in the cool 70s. Tied with 1981 as O'Hare's second warmest July 12th is 1966 with a high of 93 and low of 74. O'Hare's warmest low of the date is 75 in 1972. Prior to 1979, 1972 was also one of O'Hare's warmest as the high was 90 that day. 

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1973 the high was 90 with a low of 58, a 32 degree spread. In 1968 the high was 86 with a low of 56, a 30 degree spread. In 1965 the high was 83 with a cold low of 52 (colder than the record low), a 31 degree spread. In 1964 the high was 69 with a low of 52 (colder than the record low), a cool day. Temperatures on July 12th in 1975 and 1976 were identical (high of 76, low of 56).

More recently, there were no small spreads (7 degrees or less) or large spreads (30 degrees or more).

On the cool side, in 1990 the high was 73 with a low of 59. In 1999 the high was 82 with the record low of 53. The former record low was 55 in 1975 at Midway. The record coolest high of 65 occurred in 1940 at the University of Chicago. 19 of the last 33 lows (58%) were in the 60s. Nine lows (27%) were in the cold 50s and five lows (15%) were in the warm 70s. 1964 was O'Hare's coolest July 12th as the high was 69 (O'Hare's coolest high of the date) with a low of 52 (along with the low of 52 in 1965, O'Hare's coldest lows and colder than the record low of 53 set in 1999).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:55 and sunrise is at 5:28. Sunset is at 20:29 and twilight ends at 21:03. There's a total of 15 hours, 1 minute of daylight today and 16 hours, 8 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 4:55 and sunrise is at 5:29. The moon is waning crescent, having reached last quarter two nights ago at 20:48. Illumination was 39% at midnight, will be 34% at noon and 30% at midnight tonight. Moonrise was at 0:35 this morning. Moonset is at 15:00 this afternoon. Moonrise is at 1:08 tomorrow morning. Moonlight time is 14 hours, 25 minutes which is 28 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 ten days.