August 1: ORD

Today is August 1st. It's the 213th day of the year. 152 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 86 and 65.

On the hot side, in 2006 the high was 99 with the record warmest low of 80. In 1988 the high was the record high of 100 with the former record low of 78. In 1987 the high was 97 with a low of 77. Another hot high was 95 in 1991. Another warm low was 76 in 2001. 17 of the last 31 highs (55%) were 80s. Nine highs were in the warmer: 90s (8) and 100s (1). Six highs were in the cooler 70s. An interesting side bar is that for nine years in a row, from 1992 to 2000, there were no highs in the 90s. Through 2010, this is the average fifth hottest day of the year.

In looking back through the years to the first August at O'Hare in 1959, the following instances were notable: In 1974 the high was a cool 67 with a low of 62, a five degree spread. In 1973 the high was a cool 70. In 1965 the high was a cool 69 with a low of 54, a cool day. In 1961 the high was 77 with a low of 71, a six degree spread.

More recently, there was a large spread of 32 degrees in 1991 (95/63).

On the cool side, there were no days of a mean of at least 11.5 degrees below normal. Three days stand out as the coolest: 1990 with a high of 76 and the record low of 51. The former record low was 52 in 1947. In 1985 the high was 75 with a low of 54. In 1979 we had our coolest high (of the past 31 years) of 70 with a low of 60. The record coolest high of 66 occurred way back in 1875. The official thermometer was located near Lake Michigan at the time. 20 of the last 31 lows (65%) were 60s. Six lows were in the cooler 50s. Six were in the warmer: 70s (5) and 80s (1).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight began at 5:14 and sunrise is at 5:46. Sunset is at 20:12 and civil twilight ends at 20:44. Nautical twilight ends at 21:23 and astronomical twilight ends at 22:07. There's a total of 14 hours, 26 minutes of daylight today and 15 hours, 30 minutes between twilights. We are losing about two minutes of daylight a day. Tomorrow twilight begins at 5:16 and sunrise is at 5:47. The moon is waning gibbous and reaches last quarter tomorrow night at 23:59, a minute to midnight. Illumination was 69% at midnight, will be 64% at noon and 60% at midnight tonight. Moonset is at 12:17 this afternoon. Moonrise is at 22:49 tonight. Moonset is at 13:20 tomorrow afternoon. Moonlight time is 13 hours, 28 minutes which is 37 minutes longer than yesterday. -Bernie-