October 11: ORD

Today is October 11th. It's the 285th day of the year. 81 days remain. It's week 41 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 64 and the normal low is 44. I've calculated the 33-year averages at 65 and 43.

On the warm side, two years ago, in 2010, the high was 82 (with 1973, O'Hare's second hottest high of the date) with a low of 54. Last year, in 2011, the high was 79 with a low of 57. In 2003 the high was 78 with a low of 54.  The other warm highs were 79 degrees in: 1989, 1995, 2008 and 76 degrees in: 1974, 1983 and 1997. The record high of 87 degrees was set back in 1928 at the University of Chicago. The record warmest low of 66 degrees occurred in 1973 at Midway. 31 of the past 33 highs (94%) were in the: 50s (10), 60s (12) and 70s (9). One high was in the cold 40s (44 degrees in 2009) and one high was in the warm 80s (82 degrees in 2010). O'Hare's warmest October 11th was in 1962 as the high was 88 (O'Hare's hottest high of the date and a high warmer than the record high) with a low of 65 (O'Hare's second warmest low of the date). O'Hare's second warmest October 11th was in 1973 as the high was 82 (with 2010, O'Hare's second hottest high of the date) with a low of 66 (O'Hare's warmest low of the date). The other warm days were: 1960 with a  high of 80 (O'Hare's third hottest high of the date) and low of 53 and 1961 with a high of 77 and low of 55.

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1977 the high was a cool 51 degrees. In 1976 the high was 71 with a low of 41, a 30 degree spread. in 1975 the high was 66 with a low of 36, a 30 degree spread. In 1974 the high was a warm 76 with a low of 45, a 31 degree spread. In 1973 the high was 82 with a low of 66, a warm day and year of the record warmest low, also 66 degrees. In 1967 the high was 47 with a low of 30, a cold day. In 1966 the high was 67 with a low of 37, a 30 degree spread. In 1964 the high was 56 with a cold low of 24 (colder than the record low of 27), a cool day. In 1962 the high was 88 with a low of 65, a hot day. That high of 88 was warmer than the record high of 87. In 1961 the high was a warm 77 with a low of 55, a warm day. In 1960 the high was a warm 80 with a low of 53, a warm day. In 1959 the high was a cool 50 degrees.

More recently, there were additional large spreads of 40 degrees in 1989 (79/39), 33 degrees in 1995 (79/46) and 31 degrees in 1997 (76/45). There was a small spread of five degrees in 2005 (60/55).

On the cool side, three years ago, in 2009 (O'Hare's coolest October 11th), the high was 44 (O'Hare's coolest high of the date) with a low of 29. In 1987 the high was 50 with a low of 29. Those lows of 29 degrees are O'Hare's third coldest lows of the date. In 1996 the high was 57 with the record-tying low of 27 (O'Hare's second coldest low of the date). The record low of 27 degrees was first set nine decades earlier in 1906. In 1988 the high was 51 with a low of 33. The other cold lows were 24 degrees in 1964 (O'Hare's coldest low of the date), and 32 degrees in: 1990 and three years later in 1993. The record coolest high of 41 degrees occurred way back in 1875, at a time when the official readings were taken adjacent to Lake Michigan. 30 of the last 33 lows (91%) were in the: 30s (8), 40s (14) and 50s (8). Three lows were in the cold 20s. O'Hare's second coolest October 11th was in 1967 as the high was 47 (O'Hare's second coolest high of the date) with a low of 30. O'Hare also had cool highs of 50 degrees in 1959 and 51 degrees in 1977. 

There's an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 2009 the high was 44 with a low of 29, overall 17.5 degrees BELOW normal. Then in 2010 the high was 82 with a low of 54, overall 14 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:34 and sunrise is at 7:02. Sunset is at 18:17 and twilight ends at 18:45. There's a total of 11 hours, 15 minutes of daylight today and 12 hours, 11 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:35 and sunrise is at 7:03. The moon is waning crescent. Illumination was 22% at midnight, will be 18% at noon and 14% at midnight tonight. Moonrise was at 2:37 this morning. Moonset is at 15:57 this afternoon. Moonrise is at 3:44 tomorrow morning. Moonlight time is 13 hours, 20 minutes which is 34 minutes shorter than yesterday.

Warm Fall began September 22nd and runs for 41 days through November 1st. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the 30s and 40s occur infrequently. United Nations Day is in 13 days. Standard Time doesn't return until November 4th.