August 13: ORD

Today is August 13th. It's the 225th day of the year. 140 days remain. It's week 33 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 81 and 63.

On the hot side, in 1995 the high was 96 with the co-record warmest low of 77. In 1988 the high was 91 with the other co-record warmest low of 77. Last year, in 2010, the high was 92 with a low of 73. There were only two other 70s lows: 70 in 1985 and 1994. The record high of 98 was set in 1944. 28 of the past 32 highs (88%) were in the: 70s (10) and 80s (18). Three highs were in the hot 90s and one was 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 1974 on the 13th & 14th, the temperatures were the same: a high of 78 with a low of 64. In 1967 the high was 77 with a cold low of 42, a 35 degree spread and cool day. That low of 42 was colder than the record low. In 1964 the high was 70 with a low of 45, a cool day. That low of 45 was also colder than the record low. In 1961 the high was 81 with a cold low of 48, a 33 degree spread. That low of 48 was also colder than the record low.

More recently, there was a small spread of seven degrees in 2005 (75/68).

On the cool side, in 2004 the high was 71 with the co-record low of 51. In 1992 the high was 69 (our coolest high) with a low of 54. The other co-record low was 51 in 1982. The record coolest high of 64 occurred way back in 1883. The official thermometer was located near Lake Michigan at the time. 27 of the last 32 lows (84%) were in the: 50s (10) and 60s (17). Five lows were in the warm 70s.

As you can see, this is a day dominated by highs in the 70s or 80s and lows in the 50s or 60s. There were two long stretches of such occurrences. The first was nine years from 1979 through 1987. The second was 14 years from 1996 through 2009. The stretches were interrupted by highs in the 90s and lows in the 70s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:28 and sunrise is at 5:58. Sunset is at 19:57 and twilight ends at 20:28. There's a total of 13 hours, 59 minutes of daylight today and 15 hours between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:29 and sunrise is at 5:59. The moon is full today at 13:57 as the full Sturgeon moon. Other names for this moon are Green Corn and Grain. Illumination was 100% at midnight, will be 100% at noon and 100% at midnight tonight. Moonset is at 5:53 this morning. Moonrise is at 19:38 tonight. Moonset is at 6:56 tomorrow morning. Moonlight time is 10 hours, 15 minutes which is 37 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 23 days.