July 25: ORD

Today is July 25th. It's the 207th day of the year. 159 days remain. It's week 30 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 64. I've calculated the 33-year averages at 84 and 65.

On the hot side, in 1987 the high was 95 with a low of 74 (O'Hare's warmest low of the date). In 1999 the high was 96 (O'Hare's hottest high of the date) with a low of 73. 1987 and 1999 were O'Hare's warmest July 25ths. The record high of 101 was set in 1940 at the University of Chicago. The record warmest low of 77 occurred way back in 1892 at a time when the official readings were taken adjacent to Lake Michigan. 23 of the past 33 highs (70%) were in the 80s. O'Hare recorded six consecutive 80s highs from 1978 through 1983. Four highs (12%) were in the hot 90s. Six highs (18%) were in the cool 70s. Our most recent 70s high was 73 in 2004 (along with the high of 73 in 1959, O'Hare's coolest highs of the date).

In looking back through the years to the first July at O'Hare in 1959, the following instances were notable: In 1970, today and tomorrow (the 25th & 26th) the temperatures were the same: a high of 89 with a low of 71. In 1965 the high was 88 with a low of 58, a 30 degree spread.

More recently, there were no large or small temperature spreads.

On the cool side, in 2004 (O'Hare's coolest July 25th) the high was 73 (along with the high of 73 in 1959, O'Hare's coolest highs of the date) with a low of 60. In 1991 the high was 77 with a low of 58. O'Hare's coldest lows were 57 degrees in 1998 and 2000. The record low of 53 was set more than a century ago in 1911. The record coolest high of 64 occurred way back in 1920. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 20 of the last 33 lows (61%) were in the 60s. O'Hare recorded nine consecutive 60s lows from 1978 through 1986. Four lows (12%) were in the cold 50s. Nine lows (27%) were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:07 and sunrise is at 5:40. Sunset is at 20:19 and twilight ends at 20:52. There's a total of 14 hours, 39 minutes of daylight today and 15 hours, 45 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:08 and sunrise is at 5:41. The moon is waxing crescent, heading towards first quarter tomorrow at 3:56. Illumination was 38% at midnight, will be 43% at noon and 49% at midnight tonight. Moonrise is at 12:53 this afternoon. Moonset is at 23:34 tonight. Moonrise is at 14:04 tomorrow afternoon. Moonlight time is 10 hours, 41 minutes which is 35 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. Labor Day is in 40 days.