August 5: ORD

Today is August 5th. It's the 217th day of the year. 148 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 81 and 63.

On the hot side, there were no days of a mean of at least 11.5 degrees above normal. The warmest readings were the two 90s highs: 91 in 1984 and 90 in 1996. The warmest lows were the three in the 70s: 73 in 1996, 71 in 1998 and 70 in 1980. The record high of 102 was set back in 1918. The record warmest low of 78 was set way back in 1881. For both records, the thermometer was located near Lake Michigan. 18 of the last 31 highs were 80s. Two highs were in the warmer 90s. 11 highs were in the cooler: 60s (1) and 70s (10). Long stretches of highs under 90 characterize this day. For 11 years from 1985 through 1995 there were no 90s. For 13 years, still ongoing, from 1997 through 2009, there have been no highs in the 90s. A third of the 80s highs have been in the upper 80s (87, 88 and 89). The most recent occurred in two of the past three years (87 two years ago and 88 three years ago). Last year the high was a cooler 79.

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 a cool 50, a temperature cooler than the record low. In 1974 and 1972 the lows were 51, equal to our record low. In 1966 the high was 82 with a low of 52, a 30 degree spread. In 1962 the high was 85 with a low of 54, a 31 degree spread.

More recently, there were no large spreads of at least 30 degrees or small spreads of up to seven degrees.

On the cool side, in 1994 the high was 68 (the coolest of the past 31 years) with the record low of 51. Another cool low was 52 in 1993. Other cool lows were 53 in both 1992 and 1997. The record coolest high of 63 was set back in 1915. The official thermometer was located near Lake Michigan at the time. 22 of the last 31 lows (71%) were 60s. Six lows were in the cooler 50s. Three lows were in the warmer 70s. There were back to back to back cool days: 1992 (73/53), 1993 (76/52) and 1994 (68/51). Then there were a couple of warm days in 1995 (87/66) and 1996 (90/73). In 1997 it was cool again as the high was 73 with a low of 53.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight began at 5:19 and sunrise was at 5:50. Sunset is at 20:08 and civil twilight ends at 20:39. Nautical twilight ends at 21:17 and astronomical twilight ends at 22:00. There's a total of 14 hours, 18 minutes of daylight today and 15 hours, 20 minutes between twilights. We are losing about two minutes of daylight a day. Tomorrow twilight begins at 5:20 and sunrise is at 5:51. The moon is waning crescent. Illumination was 29% at midnight, will be 25% at noon and 20% at midnight tonight. Moonrise was at 0:41 this morning. Moonset was at 16:33 this afternoon. Moonrise is at 1:36 tomorrow morning. Moonlight time is 15 hours, 52 minutes which is 22 minutes longer than yesterday. Moonlight time is peaking. -Bernie-