June 23: ORD

Today is June 23rd. It's the 175th day of the year. 191 days remain. It's week 25 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 82 and the normal low is 61. I've calculated the 33-year averages at 81 and 60.

On the hot side, three years ago, in 2009 (O'Hare's warmest June 23rd), the high was 94 (with the high of 94 in 1968, O'Hare's hottest highs of the date) with a low of 71. In 1997 the high was 92 with a low of 72. Five years later, in 2002, the high was also 92 with a low of 72. Those lows of 72 are O'Hare's warmest lows of the date. The record high of 97 was set back in 1930 at the University of Chicago. The record warmest low of 79 occurred back in 1923, at a time when the official readings were taken adjacent to Lake Michigan. 25 of the past 33 highs (76%) were in the: 70s (11) and 80s (14). There were 11 consecutive 70s & 80s highs from 1984 through 1994. Six highs (18%) were in the hot 90s. Two highs (6%) were in the cool: 50s (1) and 60s (1).

In looking back through the years to the first June at O'Hare in 1959, the following instances were notable: In 1974 the high was a cool 63 with a low of 51, a cool day. In 1972 the high was 70 with a low of 44, a cool day. In 1969 the high was a cool 67 degrees. In 1968 the high was a hot 94 with a low of 58, a 36 degree spread. In 1963 the high was 84 with a cold low of 44, a 40 degree spread. The lows of 44 in 1963 and 1972 unofficially tied the record low.

More recently, there was one small spread of five degrees in 2007 (67/62). The additional large spreads were: 33 degrees in 2005 (93/60), 31 degrees in 1983 (93/62) and 31 degrees in 1993 (87/56).

On the cool side, in 1979 (O'Hare's coolest June 23rd) the high was 59 (O'Hare's coolest high of the date) with a low of 50. Three years later, in 1982, the high was 75 with the record low of 44, a 31 degree spread. The record coolest high of 58 occurred at Midway in 1979. The other cool high was 67 in 2007. 28 of the last 33 lows (85%) were in the: 50s (14) and 60s (14). One low was in the cold 40s. Four lows were in the warm 70s. There's a tie for O'Hare's second coolest June 23rd. In 1972 the high was 70 with a low of 44 (tied with the record low). Two years later, in 1974, the high was 63 with a low of 51. The other cold, record-tying low was 44 in 1963.  

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:43 and sunrise is at 5:18. Sunset is at 20:34 and twilight ends at 21:08. There's a total of 15 hours, 16 minutes of daylight today and 16 hours, 25 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 4:43 and sunrise is at 5:18. The moon is waxing crescent. Illumination was 13% at midnight, will be 17% at noon and 21% at midnight tonight. Moonrise was at 9:24 this morning. Moonset is at 22:56 tonight. Moonrise is at 10:29 tomorrow morning. Moonlight time is 13 hours, 32 minutes which is 34 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. Independence Day is in 11 days.