August 18: ORD

Today is August 18th. It's the 230th day of the year. 135 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 81 and the normal low is 62. I've calculated the 31-year averages at 80 and 62.

On the hot side, there were no days of a mean of at least 11.5 degrees above normal. Three days stand out as the warmest. In 1995 the high was 90 with a low of 73. In 1988 the high was 89 with a low of 72. Two years later, in 1990, the high was 91 with a low of 70. The record high of 98 was set in 1947 and the record warmest low of 79 occurred in 1972. Over the last 31 years, 28 highs were: 70s (14) and 80s (14). Two highs were in the warmer 90s and one high was in the cooler 60s.

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1972 the high was 93 with a low of 76, a hot day. 1972 was the year of the record warmest low (79 at Midway). In 1963 the high was 69 with a low of 42, a cool day and year of the record low (49 at Midway). That low of 42 is cooler than the record low. In 1962 the high was 82 with a cool low of 48, a 34 degree spread. That low of 48 is cooler than the record low. In 1961 the high was 87 with a low of 56, a 31 degree spread.

More recently, there was a large spread of 30 degrees in 1982 (83/53).

On the cool side, there were no days of a mean of at least 11.5 degrees below normal. Three days stand out as coolest. In 1981 the high was 75 with a low of 51. Three years ago the high was 68 with a low of 59. That high of 68 was the coolest high of the past 31 years. You have to go all the way back to 1963 to find the previous sub-70 degree high of 69 degrees. On that day in 1963 the low was 42, the lowest temperature of August 1963. It was also 69 on the prior day, August 17, 1963. In 1997 the high was 70 with a low of 58. The record low of 49 was set in 1963 at Midway. The record coolest high of 65 was set in 1950. Over the last 31 years, 26 lows were: 50s (11) and 60s (15). Five lows were in the warmer 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight began at 5:34 and sunrise was at 6:04. Sunset is at 19:50 and twilight ends at 20:20. There's a total of 13 hours, 46 minutes of daylight today and 14 hours, 46 minutes between twilights. We are losing two or three minutes of daylight a day. Tomorrow twilight begins at 5:35 and sunrise is at 6:05. The moon is waxing gibbous and reached first quarter two days ago at 13:14. Illumination was 65% at midnight, will be 70% at noon and 75% at midnight tonight. Moonset was at 11 minutes past midnight this morning. Moonrise is at 16:06 this afternoon. Moonset is at 1:05 tomorrow morning. Moonlight time is 8 hours, 5 minutes which is 45 minutes shorter than yesterday. Moonlight time is at it's shortest today and will begin lengthening tomorrow -Bernie-