August 11: ORD

Today is August 11th. It's the 223rd day of the year. 142 days remain. It's week 32 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 79 and 62.

On the hot side, there were no days of a mean of at least 11.5 degrees above normal. The warmest day was in 1995 when the high was 93 and the low was 72. A close second was in 1988 when the high was 92 with a low of 72. The final day with a mean of at least 80 degrees was in 2002 when the high was 93 with a low of 67. The record high of 98 was set in 1941. The record warmest low of 77 occurred in 1944. Over the last 31 years, 26 highs (84%) were: 70s (15) and 80s (11). Three highs were in the warmer 90s. Two highs were 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 1967 the high was 70 with a low of 47, a cool day. That low of 47 is equal to the current record low. In 1965 the high was 79 with a cool low of 45, a 34 degree spread (or diurnal). That low of 45 is below the current record low.

More recently, there was a large spread of 30 degrees in 1982 (77/47). The small spreads were six degrees in 1997 (70/64) and seven degrees in 1994 (67/60).

On the cool side, in 2004 the high was our record coolest high of 62 with a low of 53. In 1982 the low was 47, the record low. Other cool highs were 67 in 1994 and 70 in 1997. The previous record coolest high of 65 was set back in 1903. The official thermometer was located near Lake Michigan at the time. Over the last 31 years, 20 lows (65%) were in the 60s. Nine lows were in the cooler: 40s (1) and 50s (8). Two lows were in the warmer 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight began at 5:26 and sunrise was at 5:57. Sunset is at 20:00 and civil twilight ends at 20:30. Nautical twilight ends at 21:08 and astronomical twilight ends at 21:49. There's a total of 14 hours, 3 minutes of daylight today and 15 hours, 4 minutes between twilights. We are losing about three minutes of daylight a day. Tomorrow twilight begins at 5:27 and sunrise is at 5:58. The moon is waxing crescent. Illumination was 2% at midnight, will be 4% at noon and 7% at midnight tonight. Moonrise was at 7:54 this morning. Moonset is at 20:38 tonight. Moonrise is at 9:12 tomorrow morning. Moonlight time is 12 hours, 44 minutes which is 50 minutes shorter than yesterday. -Bernie-