October 16: ORD

Today is October 16th. It's the 290th day of the year. 76 days remain. It's week 42 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 62 and the normal low is 43. I've calculated the 33-year averages at 62 and 43.

On the warm side, in 1998 the high was 80 with a low of 55. Four years earlier, in 1994, the high was 76 with a low of 57. The other warm highs were 75 degrees in 1988 and 74 degrees in 1980. The other warm low was 57 degrees in 1996. The lows of 57 degrees in 1994 and 1996 are O'Hare's second warmest lows of the date. The record high of 87 degrees was set in 1963 at Midway. The record warmest low of 68 degrees occurred way back in 1897. The National Weather Service has this low of 68 occurring in 1879. In either event, whether 1879 or 1897, this was set at a time when the official readings were taken adjacent to Lake Michigan. 30 of the past 33 highs (91%) were in the: 50s (11), 60s (11) and 70s (8). One high was in the warm 80s (80 degrees in 1998). Two highs were in the cold 40s (both occurred recently: 45 degrees three years ago in 2009 and 47 degrees in 2004). O'Hare's warmest October 16th was in 1968 as the high was 82 (O'Hare's second hottest high of the date) with a low of 65 (O'Hare's warmest low of the date). O'Hare's second warmest October 16th was in 1963 as the high was 85 (O'Hare's hottest high of the date) with a low of 56. Another warm day was in 1965 as the high was 80 with a low of 56. 

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1970 the low was a cold 30 degrees. In 1968 the high was 82 with a low of 65, a warm day. In 1965 the high was 80 with a low of 56, a warm day. In 1964 the high was a warm 76 with a low of 37, a 39 degree spread. In 1963 the high was 85 with a low of 56, a warm day and year of the record high of 87 at Midway. In 1962 the high was 73 with a low of 42, a 31 degree spread. In 1961 the high was 70 with a low of 40, a 30 degree spread. More recently, there were large spreads of 34 degrees in 1991 (62/28), 31 degrees in 1983 (72/41) and 31 degrees last year, in 2010 (71/40). The lone small spread was six degrees two years ago, in 2009 (45/39).

On the cool side, in 1992 (O'Hare's coolest October 16th) the high was 50 with a low of 29 (O'Hare's second coldest low of the date). In 2002 (O'Hare's second coolest October 16th) the high was 50 with a low of 33. The other cool highs were 45 degrees three years ago in 2009 (O'Hare's coolest high of the date) and 47 degrees in 2004. The record low of 28 degrees was set in 1991. The record coolest high of 44 degrees occurred back in 1943 at Midway. 31 of the last 33 lows (94%) were in the: 30s (11), 40s (12) and 50s (8). The two  cold 20s lows were in the back-to-back years of 1991 and 1992. These are the only 20s lows in the history of O'Hare on October 16th. O'Hare's third coldest low of 30 degrees occurred in 1970.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:39 and sunrise is at 7:08. Sunset is at 18:09 and twilight ends at 18:37. There's a total of 11 hours, 1 minute of daylight today and 11 hours, 58 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:41 and sunrise is at 7:09. The moon is waxing crescent, having passed new yesterday at 7:02. Illumination was 1% at midnight, will be 2% at noon and 4% at midnight tonight. Moonrise was at 8:34 this morning. Moonset is at 18:51 tonight. Moonset is at 9:47 tomorrow morning. Moonlight time is 10 hours, 17 minutes which is 33 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 eight days. Standard Time doesn't return until November 4th.