June 24: ORD

Today is June 24th. It's the 176th day of the year. 190 days remain. It's week 26 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 83 and 60.

On the hot side, in 2005 (O'Hare's warmest June 24th) the high was 96 (O'Hare's hottest high of the date) with a low of 76 (O'Hare's warmest low of the date). Three years ago, in 2009 (O'Hare's second warmest June 24th), the high was 94 with a low of 75. In 1997 (O'Hare's third warmest June 24th) the high was 93 with a low of 75. Those lows of 75 are O'Hare's second warmest of the date. The other hot highs were 94 in 1995 and 94 in 1998. The record high of 97 was last set in 1953 at Midway, having originally been set in 1937 at the University of Chicago. The record warmest low of 77 occurred back in 1923, at a time when the official readings were taken adjacent to Lake Michigan. 29 of the past 33 highs (88%) were in the: 70s (8), 80s (11) and 90s (10). Four highs were in the cool 60s. 

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 67 with a low of 51, a cool day. In 1972 the high was a cool 70 degrees. In 1969 the high was a cool 66 with a low of 59, a seven degree spread. In 1967 the high was a cool 68 degrees. In 1965 the low was a cold 48 degrees. In 1963 the high was 88 with a cold low of 48, a 40 degree spread. In 1961 the low was a cold 47 degrees. In 1959 the high was 90 with a low of 60, a 30 degree spread.

More recently, the spreads were all large: 31 degrees in 1987 (91/60), 31 degrees in 1995 (94/63), 31 degrees in 2001 (81/50), 31 degrees in 2006 (82/51) and 30 degrees in 1983 (91/61). O'Hare recorded consecutive days of a spread of 40 degrees in 1963. On June 23rd, it was 84 and 44. On June 24th, it was 88 and 48.

On the cool side, in 1986 (O'Hare's coolest June 24th) the high was 61 (O'Hare's coolest high of the date) with the record low of 46. In 1979 (tied with 1974 as O'Hare's second coolest June 24th) the high was 69 with a low of 49. The other cold low was 49 in 1990. The other cool highs were 68 last year (in 2011), 69 in 1994 and 70 in 2004. The record coolest high of 59 occurred back in 1917, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 50s (12) and 60s (14). Consecutive lows in the 50s & 60s occurred as follows: six from 1980 through 1985, six from 1991 through 1996 and six from 1999 through 2004. 69% of the 50s & 60s lows occurred in the aforementioned streaks. Three lows (9%) were in the cold 40s, occurring from 1979 through 1990. Additionally, prior to 1979, O'Hare recorded three 40s lows from 1961 through 1965. Four lows (12%) were in the warm 70s. Except for 1972, all of O'Hare's 70s lows occurred from 1997 through 2009.

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 no minutes of daylight from yesterday. Tomorrow twilight begins at 4:44 and sunrise is at 5:18. The moon is waxing crescent. Illumination was 21% at midnight, will be 25% at noon and 30% at midnight tonight. Moonrise was at 10:29 this morning. Moonset is at 23:25 tonight. Moonrise is at 11:35 tomorrow morning. Moonlight time is 12 hours, 56 minutes which is 36 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 ten days.