June 25: ORD

Today is June 25th. It's the 177th day of the year. 189 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 83 and the normal low is 61. I've calculated the 33-year averages at 85 and 60.

On the hot side, in 1988 the high was the record high of 103 with a low of 66, a 37 degree spread. That high of 103 is the second hottest high ever at O'Hare. Three years ago, in 2009, the high was 94 with a low of 75 (O'Hare's warmest low of the date). 1988 and 2009 have means of 84.5 and thus are O'Hare's warmest June 25ths. The other hot high was 95 in 1998. The other warm low was 73 in 2002. The record warmest low of 76 occurred way back in 1890, at a time when the official readings were taken adjacent to Lake Michigan. 19 of the past 33 highs (58%) were in the 80s. O'Hare recorded six consecutive 80s highs from 1990 through 1995. Seven highs (21%) were in the warm: 90s (6) and 100s (1). Seven highs (21%) were in the cool 70s. O'Hare's second hottest high of the date was 96 in 1969.

In looking back through the years to the first June at O'Hare in 1959, the following instances were notable: In 1978 the high was 75 with a low of 68, a seven degree spread. In 1974 the high was 70 with a low of 49, a cool day. In 1973 the high was 84 with a low of 50, a 34 degree spread. In 1971 highs and lows were nearly the same on the 25th (81/62) and 26th (82/61). In 1970 the high was a cool 69 with a low of 52, a cool day. In 1969 the high was a hot 96 with a low of 60, a 36 degree spread. In 1968 the high was a cool 71 degrees. In 1965 the high was 73 with a cold low of 45, a cool day. In 1963 the high was 90 with a low of 53, a 37 degree spread. In 1959, highs and lows were nearly the same on the 25th (91/70) and 26th (90/71).

More recently, the additional spreads were all large: 36 degrees in 1979 (80/44), 35 degrees in 1989 (91/56), 33 degrees in 1982 (83/50), 33 degrees in 1985 (84/51), 33 degrees in 1992 (80/47) and 31 degrees in 1983 (94/63).

On the cool side, in 1986 (tied with 1965 (73/45) as O'Hare's coolest June 25th)) the high was 77 with the record low of 41, a 36 degree spread. In 2004 the high was 72 with a low of 49. The other cold lows were 44 in 1979 and 47 in 1992. The record coolest high of 56 occurred back in 1928 at the University of Chicago. 24 of the last 33 lows (73%) were in the: 50s (10) and 60s (14). O'Hare recorded six consecutive 50s & 60s lows from 1980 through 1985. Four lows (12%) were in the cool 40s and five lows (15%) were in the warm 70s. O'Hare's coolest high of the date was 69 degrees in 1970.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:44 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, 24 minutes between twilights. We lost no minutes of daylight from yesterday. Tomorrow twilight begins at 4:44 and sunrise is at 5:19. The moon is waxing crescent and will reach first quarter tomorrow at 22:30. Illumination was 30% at midnight, will be 35% at noon and 40% at midnight tonight. Moonrise was at 11:35 this morning. Moonset is at 23:54 tonight. Moonrise is at 12:43 tomorrow afternoon. Moonlight time is 12 hours, 19 minutes which is 37 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 nine days.