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 64. I've calculated the 32-year averages at 80 and 62.

On the hot side, in 1995 the high was 93 with a low of 72. Last year, in 2010, the high was 90 with a low of 75. In 1988 the high was 92 with a low of 72. The only other 90s high was 93 in 2002. The record high of 98 was set in 1941 after originally being set way back in 1874. The record warmest low of 77 occurred in 1944. 26 of the past 32 highs (81%) were in the: 70s (15) and 80s (11). Four highs were in the hot 90s. Two highs were in the cool 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 cold low of 45, a 34 degree spread (or diurnal). That low of 45 is below the current record low.

More recently, there were no other large spreads of 30 degrees or more. 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. The previous record coolest high of 65 occurred back in 1903. The official thermometer was located near Lake Michigan at the time. In 1982 the high was 77 with the record low of 47, a 30 degree spread. In 1979 the high was 71 with a low of 54. Other cool highs were 67 in 1994 and 70 in 1997. 20 of the last 32 lows (63%) were in the 60s. There was a stretch of eight consecutive years of lows in the 60s from 1996 through 2003. Nine lows were in the cool: 40s (1) and 50s (8). Three lows were in the warm 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:26 and sunrise is at 5:56. Sunset is at 20:00 and twilight ends at 20:31. There's a total of 14 hours, 4 minutes of daylight today and 15 hours, 5 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 5:27 and sunrise is at 5:57. The moon is waxing gibbous and will be full in two days at 13:57 as the full Sturgeon moon. Illumination was 93% at midnight, will be 96% at noon and 97% at midnight tonight. Moonset is at 3:43 this morning. Moonrise is at 18:38 tonight. Moonset is at 4:48 tomorrow morning. Moonlight time is 9 hours, 5 minutes which is 26 minutes longer than yesterday.

Summer began June 4 and runs for 110 days through September 21. High temperatures in this period are usually in the 70s and 80s. Highs in the 60s, 90s and 100s occur infrequently. Labor Day is in 25 days.