August 15: ORD

Today is August 15th. It's the 227th day of the year. 138 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 82 and 63.

On the hot side, in 1988 the high was 94 with a low of 74. In 2000 the high was 92 with a low of 71. In 1983 the high was 90 with a low of 72. The only other 90s high was 90 in 1987. The record high of 98 was set in 1944. The record warmest low of 76 occurred in 1938. 27 of the past 32 highs (84%) were in the: 70s (10) and 80s (17). Four 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 1964 the high was 78 with a cold low of 41, a 37 degree spread and cool day. That low of 41 is colder than the record low. In 1963 the low was a cool 50 degrees.

More recently, there was a large spread of 33 degrees in 1984 (87/54).

On the cool side, in 1979 the high was 69 (our only 60s high) with a low of 46. That low of 46 is colder than the record low. In 2004 the high was 75 with the record low of 48. The former record low of 51 was set at Midway in 1964. In 1992 the high was 71 with a low of 52. The record coolest high of 64 occurred way back in 1894. The official thermometer was located near Lake Michigan at the time. 18 of the last 32 lows (56%) were in the 60s. Seven lows (22%) were in the cool: 40s (2) and 50s (5). Seven lows (22%) were in the warm 70s.

As you can see, this is a day dominated by highs in the 70s or 80s. There's an ongoing long stretch of such highs. This is ten years from 2001 through last year, 2010. There was an 11 year stretch from 1989 through 1999.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:30 and sunrise is at 6:00. Sunset is at 19:54 and twilight ends at 20:25. There's a total of 13 hours, 54 minutes of daylight today and 14 hours, 55 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:31 and sunrise is at 6:02. The moon is waning gibbous, having passed full two days ago at 13:57 as the full Sturgeon moon. Other names for this moon are Green Corn and Grain. Illumination was 98% at midnight, will be 96% at noon and 94% at midnight tonight. Moonset is at 7:57 this morning. Moonrise is at 20:27 tonight. Moonset is at 8:57 tomorrow morning. Moonlight time is 11 hours, 30 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 21 days.