June 30: ORD

Today is June 30th. It's the 182nd day of the year. 184 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 84 and the normal low is 62. I've calculated the 33-year averages at 80 and 59.

On the hot side, in 1996 the high was 94 (O'Hare's hottest high of the date) with a low of 73. In 2005 the high was 91 with a low of 72. In 2002 the high was 93 (ties 1970 as O'Hare's second hottest high of the date) with a low of 69. The record high of 99 was tied in 1953 at Midway, after first being set in 1913. The record warmest low of 80 occurred back in 1931 at the University of Chicago. 26 of the past 33 highs (79%) were in the: 70s (10) and 80s (16). O'Hare recorded 14 consecutive 70s & 80s highs from 1972 through 1985. Four highs (12%) were in the hot 90s and three (9%) were in the cool 60s. O'Hare's warmest June 30th was in 1970 as the high was 93 (tied with 2002 as O'Hare's second hottest high of the date) with a low of 78 (O'Hare's warmest low of the date).

In looking back through the years to the first June at O'Hare in 1959, the following instances were notable: In 1970 the high was 93 with a warm low of 78, a hot day. In 1966 the high was 90 with a low of 60, a 30 degree spread. In 1965 the high was 68 with a low of 44, a cool day. In 1963 the high was 92 with a low of 62, a 30 degree spread.

More recently, there was an additional small spread of seven degrees three years ago, in 2009 (66/59). The large spreads were: 34 degrees in 1989 (83/49), 32 degrees in 2006 (85/53) and 30 degrees in 1979 (81/51).

On the cool side, in 1982 (O'Hare's second coolest June 30th) the high was 70 with a low of 47 (O'Hare's second coldest low of the date). Four years later, in 1986, the high was 64 (O'Hare's coolest high of the date) with a low of 59, a small five degree spread. The other 40s low was 49 in 1989. The other cool highs were 66 three years ago in 2009, 69 in 1993, 72 in 1984 and 72 in 1988. The record low of 45 was set in 1943 at Midway. The record coolest high of 59 occurred way back in 1902, at a time when the official readings were taken adjacent to Lake Michigan. 29 of the last 33 lows (88%) were in the: 50s (18) and 60s (11). Two lows were in the cold 40s and two were in the warm 70s. O'Hare's coolest June 30th was in 1965 as the high was 68 with a low of 44 (O'Hare's coldest low of the date).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:46 and sunrise is at 5:20. Sunset is at 20:34 and twilight ends at 21:08. There's a total of 15 hours, 14 minutes of daylight today and 16 hours, 22 minutes between twilights. We lost no minutes of daylight from yesterday. Tomorrow twilight begins at 4:47 and sunrise is at 5:21. The moon is waxing gibbous, heading towards the full Buck moon in three days at 13:52. Illumination was 83% at midnight, will be 87% at noon and 91% at midnight tonight. Moonset was at 2:16 this morning. Moonrise is at 17:29 this afternoon. Moonset is at 3:08 tomorrow morning. Moonlight time is 8 hours, 47 minutes which is 29 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 four days.