August 10: ORD

Today is August 10th. It's the 222nd day of the year. 143 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 83 and the normal low is 64. I've calculated the 32-year averages at 82 and 64.

On the hot side, last year (in 2010) the high was 89 with a low of 75. In 1992 the high was 91 with a low of 68. Three years later, in 1995, the high was 89 with a low of 70. The other 90s highs were 91 in 1983 and 90 in 2005. The record high of 99 was set in 1944. Other warm lows were 74 in 2006 and 73 in 1988. The record warmest low of 79 occurred in 1938. 19 of the past 32 highs (59%) were in the 80s. Three highs (10%) were in the hot 90s. Ten highs (31%) were in the cool: 60s (3) and 70s (7).

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 75 with a low of 72, a three degree spread. In 1972 the low was a cool 52 degrees. In 1967 the high was a cool 69 with a low of 53, a cool day. In 1966 the high was a cool 67 with a low of 61, a six degree spread. In 1965 the high was 70 with a low of 50, a cool day. In 1960 the high was a cool 68 degrees.

More recently, there was a large spread of 30 degrees in 2002 (89/59). The small spreads were five degrees in 2006 (79/74), seven degrees in 1988 (80/73) and seven degrees in 2004 (67/60).

On the cool side, in 1982 the high was 68 with the record low of 49. The record low of 49 was originally set a decade earlier, in 1972. In 1994 the high was 67 with a low of 56. The other cool 60s high (and most recent) was 67 in 2004. The record coolest high of 66 was set way back in 1882. The official thermometer was located near Lake Michigan at the time. 20 of the last 32 lows (62%) were in the 60s. There were two 5-year stretches of 60s lows. These were 1983 to 1987 and 1997 to 2001. Six lows (19%) were in the cool: 40s (1) and 50s (5). Six lows (19%) were in the warm 70s, including four of the last five (74 in '06, 70 in '07, 58 in '08, 70 in '09 and 75 in '10).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:24 and sunrise is at 5:55. Sunset is at 20:01 and twilight ends at 20:32. There's a total of 14 hours, 6 minutes of daylight today and 15 hours, 8 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:26 and sunrise is at 5:56. The moon is waxing gibbous and will be full in three days at 13:57 as the full Sturgeon moon. Illumination was 87% at midnight, will be 90% at noon and 93% at midnight tonight. Moonset is at 2:39 this morning. Moonrise is at 18:00 tonight. Moonset is at 3:43 tomorrow morning. Moonlight time is 8 hours, 39 minutes which is 17 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 26 days.