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 31-year averages at 83 and 65.

On the hot side, in 1988 the high was 97 with the record warmest low of 78. Other 90s highs were 93 in 1980 and 90 in 1984. Another warm low was 76 in 2005. The record high of 100 was set in 1947. 20 of the last 31 highs (65%) were 80s. Three highs were in the warmer 90s. Eight highs were in the cooler 70s. For the last 21 years, 1989 to 2009, there have been no highs in the 90s. It did hit 89 three times during this time (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 49, a temperature cooler than the record low. In 1974 the high was a cool 70. 1970 and 1971 had cool highs of 71. In 1966 the high was 81 with a cool low of 48, a 33 degree spread. That low of 48 was cooler than the record low.

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

Two 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, there were no days of a mean of at least 11.5 degrees below normal. The coolest days were: 1992 (72/53). That low of 53 is the record low and originally it was set way back in 1894. In 1993 the high was 73 with a low just a degree above the record (54). Another low of 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 31 lows (61%) were 60s. Six lows were in the cooler 50s and six were in the warmer 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight began at 5:18 and sunrise is at 5:49. Sunset is at 20:09 and civil twilight ends at 20:40. Nautical twilight ends at 21:19 and astronomical twilight ends at 22:02. There's a total of 14 hours, 20 minutes of daylight today and 15 hours, 22 minutes between twilights. We are losing about two minutes of daylight a day. Tomorrow twilight begins at 5:19 and sunrise is at 5:50. The moon is waning crescent. Illumination was 39% at midnight, will be 34% at noon and 29% at midnight tonight. Moonrise was at 23:56 last night. Moonset was at 15:30 this afternoon. Moonrise is at 0:41 tomorrow morning. Moonlight time is 15 hours, 30 minutes which is 61 minutes longer than yesterday. -Bernie-