August 19: ORD

Today is August 19th. It's the 231st day of the year. 134 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 63. I've calculated the 32-year averages at 80 and 62.

On the hot side, in 1983 the high was the record high of 99 with a low of 71. The record high of 99 was originally set in 1947. In 1995 the high was 89 with a low of 72. In 1980 the high was 91 with a low of 69. There were two other lows in the 70s: 71 in 1993 and 70 in 1988. The record warmest low of 82 occurred back in 1916. 29 of the past 32 highs (91%) were in the: 70s (13) and 80s (16). Two 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 1977 the low was a cool 51 degrees. In 1968 the low was a warm 75 degrees. In 1967 the high was a cool 64 with a low of 57, a seven degree spread and cool day. In 1964 the high was 82 with a cold low of 49, a 33 degree spread. That low of 49 is colder than the record low.

More recently, there were small spreads of four degrees in 1988 (74/70) and six degrees in 2007 (68/62).

On the cool side, in 1992 the high was 74 with the record low of 51. In 1985 the high was 72 with a low of 55. The record coolest high of 68 occurred in 2007. You have to go back 40 years to 1967 to find the previous sub-70 degree high of 64 degrees. Other cool highs are 70 in 1991, 71 in 1997 and 71 in 2000. The record coolest high of 62 was set way back in 1897. The official thermometer was located near Lake Michigan at the time. 28 of the last 32 highs (88%) were in the: 50s (13) and 60s (15). Four lows were in the warm 70s.

As you can see, this is a day dominated by highs in the 70s and 80s and lows in the 50s and 60s. There was a long 23 year stretch of such highs. This was from 1984 through 2006. There's an ongoing, 15 year stretch of lows in the 50s and 60s. This began in 1996 and continues as of last year, 2010.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:35 and sunrise is at 6:05. Sunset is at 19:48 and twilight ends at 20:18. There's a total of 13 hours, 43 minutes of daylight today and 14 hours, 43 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:36 and sunrise is at 6:06. The moon is waning gibbous, heading towards last quarter in two days at 16:54. Illumination was 74% at midnight, will be 70% at noon and 66% at midnight tonight. Moonset is at 11:56 this morning. Moonrise is at 22:11 tonight. Moonset is at 12:55 tomorrow afternoon. Moonlight time is 13 hours, 45 minutes which is 30 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 17 days.