August 31: ORD

Today is August 31st. It's the 243rd day of the year. 122 days remain. It's week 35 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 78 and the normal low is 59. I've calculated the 31-year averages at 80 and 59.

On the hot side, there were no days of a mean of at least 11.5 degrees above normal. 2000 stands out as the warmest as the high was 92 with a low of 68. The only other 90s high was 90 two years ago. The only 70s low was 71 in 1980. The record high of 99 was set in 1953. The record warmest low of 76 was set in 1941. Over the last 31 years, 28 highs (90%) were: 70s (13) and 80s (15). Two highs were in the warmer 90s and one high was in the 60s (last year's high of 68).

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 90 with a low of 72, a hot day. In 1976 the high was a hot 90. In 1975 the high was 72 with a low of 65, a seven degree spread. In 1973 the high was 89 with a warm low of 73, a hot day. In 1969 the low was a warm 72. In 1967 the high was 67 with a cool low of 47, a cool day. In 1961 the high was a hot 92 with a low of 62, a 30 degree spread. In 1960 the high was a hot 93 with a low of 70, a hot day.

More recently, there were large spreads of 31 degrees in 1984 (82/51) and 30 degrees two years ago (90/60).

On the cool side, there were no days of a mean of at least 11.5 degrees below normal. The coolest day by far was last year when the high was just 68. It was the first 60s high of the past 31 years (the first in 42 years) and just the third 60s high in O'Hare's history (67 in 1967 and 68 in 1965 were the others) with a low of 49. That low of 49 was the first 40s low of the past 31 years (the first in 42 years) and just the third 40s low in O'Hare's history (47 in 1967 and 49 in 1964 were the others). There were three highs in the lower 70s (70 in 2003, 71 in 1994 and 72 in 1987). The record low of 47 was set way back in 1872. The record coolest high of 62 occurred way back in 1892. Over the last 31 years, 29 lows (94%) were in the: 50s (14) and 60s (15). One low was in the cool 40s and one was in the warmer 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:49 and sunrise is at 6:18. Sunset is at 19:29 and twilight ends at 19:58. There's a total of 13 hours, 11 minutes of daylight today and 14 hours, 9 minutes between twilights. We are losing two or three minutes of daylight a day. Tomorrow twilight begins at 5:50 and sunrise is at 6:19. The moon is waning gibbous. Illumination was 65% at midnight, will be 60% at noon and 55% at midnight tonight. Moonset is at 13:18 this afternoon and moonrise is at 22:36 tonight. Moonset is at 14:20 tomorrow afternoon. Moonlight time is 14 hours, 42 minutes which is 23 minutes longer than yesterday.

Labor Day is in six days and Patriot Day is in 11 days. -Bernie-