August 17: ORD

Today is August 17th. It's the 229th day of the year. 136 days remain. It's week 33 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 82 and the normal low is 63. I've calculated the 31-year averages at 82 and 63.

On the hot side, in 1988 the high was the record high of 98 with a low of 77. There were two other highs in the 90s: 94 in 1983 and 93 in 1995. There were four other 70s lows: 72 in 1995, 71 in 2003 and 70 in 1990 and 70 last year. The record warmest low of 78 occurred back in 1972. Over the last 31 years, 28 highs were: 70s (11) and 80s (17). Three highs were in the warmer 90s.

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1976 the high was 80 with a low of 47, a 33 degree spread. That low of 47 was cooler than the record low and 1976 is the year of the record low (48 at Midway). In 1972 the high was 92 with a warm low of 77, a hot day. 1972 is the year of the record warmest low (78 at Midway). In 1966 the high was 88 with a low of 57, a 31 degree spread. In 1963 the high was 69 with a cool low of 46, a cool day. That low of 46 is cooler than the record low. In 1962 the high was 81 with a cool low of 51, a 30 degree spread.

More recently, there was a small spread of four degrees in 1990 (74/70).

On the cool side, there were no days of a mean of at least 11.5 degrees below normal. Two days stand out as coolest. In 1981 the high was 73 with a low of 51 and in 1992 the high was 77 with a low of 49. The record low of 48 was set in 1976. The record coolest high of 66 occurred back in 1924. The official thermometer was located near Lake Michigan at the time. Over the last 31 years, 17 lows were 60s. Nine lows were in the cooler: 40s (1) and 50s (8). Five lows were in the warmer 70s, including last year's low of 70.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight began at 5:33 and sunrise was at 6:03. Sunset is at 19:51 and twilight ends at 20:21. There's a total of 13 hours, 48 minutes of daylight today and 14 hours, 48 minutes between twilights. We are losing two or three minutes of daylight a day. Tomorrow twilight begins at 5:34 and sunrise is at 6:04. The moon is waxing gibbous and reached first quarter yesterday at 13:14. Illumination was 55% at midnight, will be 61% at noon and 65% at midnight tonight. Moonrise is at 15:10 this afternoon. Moonset is at 11 minutes past midnight tonight. Moonrise is at 16:06 tomorrow afternoon. Moonlight time is 8 hours, 50 minutes which is 28 minutes shorter than yesterday. -Bernie-