August 25: ORD

Today is August 25th. It's the 238th day of the year. 128 days remain. It's week 34 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 81 and the normal low is 62. I've calculated the 33-year averages at 82 and 63.

On the hot side, in 2003 (O'Hare's second warmest August 25th) the high was the co-record high of 95 with a low of 71. In 1995 the high was 90 with a low of 73 (O'Hare's co-warmest low of the date). The other co-record high of 95 occurred four years earlier in 1991 with a low of 66. The record highs of 95 were originally set at Midway in 1953 and 1959. The record warmest low of 74 occurred in 1959 at Midway. Since 1959 has both a co-record high and record warmest low, it is the hottest August 25th. 28 of the past 33 highs (85%) were in the: 70s (10) and 80s (18). Four highs were in the hot 90s. One high (62 in 1987) was in the cool 60s. O'Hare's warmest August 25th was in 1959 as the high was 94 with a low of 73 (O'Hare's other co-warmest low of the date).  

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1977 the high was 79 with a cold low of 48, a 31 degree spread. That low of 48 was just above the record low. 1969 was the start of four consecutive days of highs of 86 degrees (from the 25th to the 28th). In 1967 the high was 82 with a cold low of 50, a 32 degree spread. In 1964 the high was 74 with a cold low of 47 (equal to the record low). In 1960 today and tomorrow (the 25th & 26th), we had lots of sixes, sevens and eights. On the 25th, it was 86 and 68. On the 26th, it was 88 and 66. In both cases, the means were 77 degrees! In 1959 the high was a hot 94 with a low of 73, a hot day. 1959 is the year of one of the co-record highs and is the year of the record warmest low.

More recently, there was an additional small spread of seven degrees in 1999 (high of 73, low of 66).

On the cool side, in 1987 (O'Hare's coolest August 25th) the high was the record coolest high of 62 with a low of 56. The former record coolest high of 63 occurred in 1965. In 1985 the high was 73 with a low of 56. Three years earlier, in 1982, the high was 75 with a low of 54. In 1997 the high was 72 with a low of 58. The record low of 47 was set back in 1917, at a time when the official readings were taken adjacent to Lake Michigan. 20 of the last 33 lows (61%) were in the 60s. Ten lows (30%) were in the cold 50s. Three lows (9%) were in the warm 70s. O'Hare's second coolest August 25th was in 1964 as the high was 74 with a low of 47 (O'Hare's coldest low of the date). This low of 47 is tied with the record low. O'Hare's second coldest low is 48 degrees in 1977. Another cold low is 50 degrees in 1967.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:42 and sunrise is at 6:12. Sunset is at 19:38 and twilight ends at 20:07. There's a total of 13 hours, 26 minutes of daylight today and 14 hours, 25 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:44 and sunrise is at 6:13. The moon is waxing gibbous, having reached first quarter yesterday at 8:54. Illumination was 58% at midnight, will be 63% at noon and 69% at midnight tonight. Moonrise is at 15:15 this afternoon. Moonset is at 0:50 tomorrow morning. Moonrise is at 16:10 tomorrow afternoon. Moonlight time is 8 hours, 45 minutes which is 53 minutes shorter than yesterday. Moonlight time is nearly at its shortest today.

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 nine days.