September 10: ORD

Today is September 10th. It's the 254th day of the year. 112 days remain. It's week 37 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 77 and the normal low is 57. I've calculated the 33-year averages at 79 and 58.

On the hot side, in 1983 (O'Hare's warmest September 10th) the high was the record high of 95 with a low of 67. Three years later, in 1986 (O'Hare's second warmest September 10th), the high was 90 with a low of 70 (O'Hare's second warmest low of the date). In 2005 the high was 92 with a low of 67. The other warm high of 89 degrees occurred in 2002. O'Hare's warmest low of the date is 72 degrees in 2000. The record warmest low of 75 occurred way back in 1912, a time when the official readings were taken adjacent to Lake Michigan. 25 of the past 33 highs (76%) were in the: 70s (12) and 80s (13). Three highs (9%) were in the hot 90s. Five highs (15%) were in the cool 60s. In 1996, today was the last day of a high in the 80s, the earliest such occurrence of the past 33 years. For nine consecutive years, from 1996 through 2004, highs were in the 70s & 80s. O'Hare's pre-1979 warm days were in: 1964 (O'Hare's second hottest high of the date of 93 degrees with a low of 65) and 1978 (high of 92, low of 65). O'Hare also had a hot high of 89 degrees in 1961.

In looking back through the years to the first September at O'Hare in 1959, the following instances were notable: in 1978 the high was a hot 92 with a low of 65, a hot day. In 1972 the high was a cool 64 degrees. In 1971 the low was a warm 69 degrees. In 1968 the high was a cool 61 with a low of 55, a six degree spread. In 1967 the high was 65 with a low of 45, a cool day. In 1966 the high was 84 with a low of 47, a 37 degree spread. In 1964 the high was a hot 93 with a low of 65, a hot day. In 1961 the high was a hot 89 degrees. In 1959 the high was a cool 65 degrees.

More recently, there was a large spread of 36 degrees in 1988 (86/50) and a small spread of four degrees in 2006 (64/60).

On the cool side, in 1995 (O'Hare's co-coolest September 10th) the high was 64 with a low of 46, O'Hare's second coldest low of the date. That high of 64 degrees shares the 64 degree high in 2006 as O'Hare's second coolest highs of the date. In 1993 the high was 65 with a low of 47. The record low of 44 degrees was set in 1943 at Midway. The record coolest high of 53 degrees occurred way back in 1917, a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 50s (12) and 60s (14). O'Hare recorded consecutive 50s & 60s lows as follows: nine from 1977 through 1985, six from 1987 through 1992 and seven from 2001 through 2007. Five lows (15%) were in the cold 40s. Two lows (6%) were in the warm 70s. O'Hare's other co-coolest September 10th was in 1967 as the high was 65 with a low of 45 (O'Hare's coldest low of the date). O'Hare's coolest high of the date is 61 degrees in 1968.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:00 and sunrise is at 6:29. Sunset is at 19:11 and twilight ends at 19:39. There's a total of 12 hours, 42 minutes of daylight today and 13 hours, 39 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:01 and sunrise is at 6:30. The moon is waning crescent, having reached last quarter two days ago at 8:15. Illumination was 34% at midnight, will be 30% at noon and 25% at midnight tonight. Moonrise was at 0:45 this morning. Moonset is at 15:45 this afternoon. Moonrise is at 1:43 tomorrow morning. Moonlight time is 15 hours which is three minutes shorter than yesterday. Moonlight time is at its peak today and was 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 60s, 90s and 100s occur infrequently. 9/11 Remembrance Day is tomorrow.