August 4: ORD

Today is August 4th. It's the 216th day of the year. 149 days remain. It's week 31 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.

According to the National Climatic Data Center (NCDC), the normal high is 83 and the normal low is 64. I've calculated the 32-year averages at 83 and 66.

On the hot side, in 1988 the high was 97 (our most recent 90s high) with the record warmest low of 78. In 2005 the high was 88 with a low of 76. The other 90s highs were 93 in 1980 and 90 in 1984. Other warm lows were 74 in both 1982 and two decades later in 2002. The record high of 100 was set in 1947. 21 of the past 32 highs (66%) were in the 80s. Three highs (9%) were in the hot 90s. Eight highs (25%) were in the cool 70s. Our most recent 70s high was 74 in 2004. For the past 22 years (1989-2010), there have been no highs in the 90s. It did hit 89 three times during this time (in 1989, 2002 and 2006).

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1978 the low was a cold 49, a temperature colder than the record low. In 1974 the high was a cool 70 degrees. 1970 and 1971 had cool highs of 71 degrees. In 1966 the high was 81 with a cold low of 48, a 33 degree spread. That low of 48 was colder than the record low.

More recently, there was a small spread of four degrees in 1998 (72/68).

Three years ago O'Hare recorded 2.43 inches of rain and Rockford had 1.22 inches. I noted that I hadn't seen lightning as severe as this in a long time. This was at the Crystal Lake train depot parking lot.

On the cool side, in 1992 the high was 72 with the record low of 53. That low of 53 was originally set way back in 1880 and tied way back in 1894. The next year, 1993, saw a high of 73 with a low of 54, just a degree above the record. Our most recent 50s low (54) occurred in 2000. In 1985 the high was 72 with a low of 56. The only other high of 72 (the coolest) occurred in 1998. The record coolest high of 62 was set back in 1915. The official thermometer was located near Lake Michigan at the time. 19 of the last 32 lows (59%) were in the 60s. Six lows (19%) were in the cool 50s. Seven lows (22%) were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:18 and sunrise is at 5:49. Sunset is at 20:09 and twilight ends at 20:41. There's a total of 14 hours, 20 minutes of daylight today and 15 hours, 23 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:19 and sunrise is at 5:50. The moon is waxing crescent and will reach first quarter in two days at 6:08. Illumination was 26% at midnight, will be 31% at noon and 36% at midnight tonight. Moonrise is at 11:47 this morning. Moonset is at 22:34 tonight. Moonrise is at 13:00 tomorrow afternoon. Moonlight time is 10 hours, 47 minutes which is 42 minutes shorter than yesterday.

Summer began June 4 and runs for 110 days through September 21. High temperatures in this period are usually in the 70s and 80s. Highs in the 60s, 90s and 100s occur infrequently. Labor Day is in 32 days.