October 20: ORD

Today is October 20th. It's the 293rd day of the year. 72 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 was on the south side of Chicago at Midway International Airport (MDW), beginning on Wednesday, July 1, 1942. Before that, 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 61 and the normal low is 42. I've calculated the 32-year averages at 60 and 42.

On the warm side, in 1979 the high was 80 with a low of 68. The record warmest low of 68 occurred also in 1979 at Midway. This was also the only 60s low in O'Hare's history on October 20th. In 2000 the high was 77 with a low of 55. Three years later, in 2003, the high was 85 with a low of 46, a 39 degree spread. The only other 80s high on October 20th in the history of O'Hare was 81 in 1971. The other warm highs were 74 in 1986 and 73 in 2007. The record high of 86 was set in 1953 at Midway. 18 of the past 32 highs (56%) were in the 50s. 12 highs (38%) were in the warm: 60s (5), 70s (5) and 80s (2). Two highs (6%) were in the cold 40s.

In looking back through the years to the first October at O'Hare in 1959, the following instances were notable: in 1978 the high was a warm 73 with a low of 35, a 38 degree spread. In 1976 the high was a cold 47 degrees. In 1975 the high was 72 with a low of 40, a 32 degree spread. In 1974 the high was 47 with a low of 30, a cold day. In 1972 the high was 49 with a low of 25, a cold day. In 1971 the high was 81 with a low of 59, a warm day. In 1970 the high was 55 with a low of 51, a four degree spread. In 1966 the high was 63 with a low of 32, a 31 degree spread. In 1965 the high was 68 with a warm low of 59, a warm day. In 1964 the high was 45 with a low of 23, a cold day. That low of 23 was colder than the record low. In 1961 the high was a cold 48 with a low of 45, a three degree spread. In 1960 the high was 45 with a low of 29, a cold day. Tom Skilling reported on his blog that back in 1952, three inches of lake-effect snow fell in Chicago but melted quickly. The high that day was just 41 with a low of 29.

More recently, there was a large spread of 35 degrees in 1986 (74/39). There were small spreads of three degrees in 2004 (53/50), four degrees in 1983 (52/48) and six degrees in 1985 (57/51).

On the cold side, in 1989 the high was 41 with a low of 34. In 2002 the high was 52 with a low of 29. The only other 40s high was 49 in 1995. Just two of the eight 40s highs in O'Hare's history occurred over the last 32 years. The other cold low was 29 in 1991. O'Hare has had a total of five lows in the 20s in it's history on October 20th, two of them over the last 32 years. The record low of 24 was last set in 1930 but originally set way back in 1895. The record coolest high of 36 occurred way back in 1895. As you can see, 1895 was by far the coldest of all October 20ths. Official readings were taken adjacent to Lake Michigan in 1895 and in 1930. 26 of the last 32 lows (81%) were in the: 30s (11) and 40s (15). There were four long streaks of lows in the 30s & 40s since 1979: first: 5 years from 1980-1984; second: 5 years from 1986-1990; third: 8 years from 1992-1999; fourth: six years from 2005-2010 (ongoing). Two lows were in the cold 20s. Four lows were in the warm: 50s (3) and 60s (1).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:43 and sunrise is at 7:12. Sunset is at 18:04 and twilight ends at 18:32. There's a total of 10 hours, 52 minutes of daylight today and 11 hours, 49 minutes between twilights. We lost four minutes of daylight from yesterday. Tomorrow twilight begins at 6:44 and sunrise is at 7:13. The moon is waning crescent and reached last quarter last night at 22:30. Illumination was 49% at midnight, will be 44% at noon and 38% at midnight tonight. Moonset is at 14:20 this afternoon. Moonrise is at 0:56 tomorrow morning. Moonset is at 14:52 tomorrow afternoon. Moonlight time is 14 hours, 20 minutes which is 25 minutes longer than yesterday.

Warm Fall began September 22 and runs for 41 days through November 1. 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 four days.