September 3: ORD

Today is September 3rd. It's the 247th day of the year. 119 days remain. It's week 36 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. Before this, the official site of record was on the south side of Chicago at Midway International Airport (MDW), beginning on Wednesday, July 1, 1942. From Friday, January 1, 1926 through Tuesday, June 30, 1942, the official site was at the University of Chicago. Before this, the official site was at various locations in Chicago going back to Monday, October 16, 1871. Observations taken from October 15, 1870 to October 8, 1871 were lost in the Great Chicago Fire.

According to the National Climatic Data Center (NCDC), the normal high is 79 and the normal low is 60. I've calculated the 33-year averages at 80 and 60.

On the hot side, in 1985 the high was 88 with a low of 72 (O'Hare's co-second warmest low of the date). Last year, in 2011, the high was 89 with a low of 69. The lone hot high (post-1978) was 91 degrees in 1983. The record high of 97 was set in 1953. The record warmest low of 75 occurred in 1973. Both records were set at Midway. 28 of the past 33 highs (84%) were in the: 70s (11) and 80s (17). Two highs were in the hot 90s. Three highs were in the cool 60s. There were two long stretches of highs in the 70s & 80s. The first was ten years from 1984 through 1993. The second was 12 years from 2000 through last year, 2011. O'Hare's warmest September 3rd was in 1960 as the high was 96 (O'Hare's hottest high of the date) with a low of 72 (O'Hare's co-second warmest low of the date). O'Hare's other co-second warmest September 3rd was in 1973 as the high was 92 with a low of 70. O'Hare's warmest low of the date, 73 degrees, occurred in 1971. O'Hare's second hottest high of the date, 94 degrees, occurred in 1964. 

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1974 the high was 64 with a low of 46, a cool day. That low of 46 was colder than the record low of 47 and 1974 is the year of the record low. In 1973 the high was a hot 92 with a low of 70, a hot day. 1973 is the year of the record warmest low of 73. In 1971 the low was a warm 73 degrees. In 1967 the high was 76 with a cold low of 44, a 32 degree spread. That low of 44 was colder than the record low. In 1964 the high was a hot 94 with a low of 67, a hot day. In 1960 the high was 96 with a low of 72, a hot day.

More recently, there was a large spread of 31 degrees in 1983 (91/60). There was a small spread of six degrees in 1981 (66/60).

On the cool side, in 1997 (O'Hare's second coolest September 3rd) the high was 67 with a low of 50. A decade earlier, in 1987, the high was 72 with a low of 49. The other cool high is 66 degrees in 1981. The other cold low of 48 degrees occurred in 1982. The record low of 47 was set in 1974 at Midway. The record coolest high of 59 occurred way back in 1891, at a time when the official readings were taken adjacent to Lake Michigan. 30 of the last 33 lows (91%) were in the: 50s (14) and 60s (16). Two lows were in the cold 40s. One low was in the warm 70s (72 in 1985). There's an ongoing, long period of lows in the 50s and 60s. This 24-year stretch began in 1988 and is still going as of last year (2011). O'Hare's coolest September 3rd was in 1974 as the high was 64 (O'Hare's coolest high of the date) with a low of 46 (colder than the record low). O'Hare's coldest low of 44 degrees occurred in 1967 (a low colder than the record low).  

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:53 and sunrise is at 6:21. Sunset is at 19:23 and twilight ends at 19:52. There's a total of 13 hours, 2 minutes of daylight today and 13 hours, 59 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 5:54 and sunrise is at 6:22. The moon is waning gibbous after reaching the full Corn (a.k.a. Green Corn or Grain) moon three days ago at 8:58. Since this was the second full moon of August, it was also the Blue moon. Illumination was 93% at midnight, will be 90% at noon and 87% at midnight tonight. Moonset is at 9:35 this morning. Moonrise is at 20:36 tonight. Moonset is at 10:35 tomorrow morning. Moonlight time is 12 hours, 59 minutes which is 34 minutes longer than yesterday. 

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