November 20: ORD

Today is November 20th. It's the 324th day of the year. 41 days remain. It's week 47 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 46 and the normal low is 31. I've calculated the 33-year averages at 46 and 31.

On the warm side, in 1982 the high was 66 with a low of 42. A decade later, in 1992, the high was 63 with a low of 40. Two years later, in 1994, the high was 59 with a low of 44. In 2007 the high was 55 with a low of 45. In 2003 the high was 65 (our most recent 60s high) with a low of 34, a 31 degree spread. The other warm highs were 60 in 1979 and 58 in: 1983 and the back-to-back years of 1989 and 1990. The other warm low was 43 in 2004. The record high of 68 was set back in 1930 and originally in 1913. The record warmest low of 62 occurred back in 1913. Both records occurred at a time when the official readings were taken adjacent to Lake Michigan. 27 of the past 33 highs (82%) were in the: 30s (8), 40s (10) and 50s (9). Three notable stretches of 30s, 40s & 50s highs occurred: 1. six years from 1986 through 1991, 2. seven years from 1993 through 1999 and 3. seven years from 2004 through last year, 2010. Four highs (12%) were in the warm 60s. Two pre-1978 highs in the 60s occurred: 60 in both 1975 and 1977. Two highs (6%) were in the cold 20s. Just one 20s high occurred prior to 1978: 28 in 1969.

In looking back through the years to the first November at O'Hare in 1958, the following instances were notable: in 1977 the high was a warm 60 degrees. In 1975 the high was a warm 60 degrees. In 1973 the high was a warm 58 with a low of 42, a warm day. In 1969 the high was 28 with a low of 15, a cold day. In 1968 the high was a cold 30 degrees with a low of 22, a cold day. In 1967 the high was a cold 34 with a low of 32, a mere two degree spread. In 1964 the high was 32 with a low of 13, a cold day. In 1963 low was a warm 44 degrees.

More recently, there were no other large spreads. There were small spreads of four degrees in 1986 (37/33), seven degrees in 1978 (32/25), and seven degrees in 1998 (34/27).

On the cold side, in 1985 the high was 27 with a low of 17. In 2000 the high was 29 (our most recent 20s high) with a low of 18 (our most recent 10s low). The other cold low was 18 in 1984. Note that back-to-back 10s lows occurred in 1984 & 1985. The other cold highs were 32 in 1978, 33 in 1987, 34 in 1996 and 34 in 1998. The record low of 8 was set way back in 1873. The record coldest high of 20 occurred way back in 1887. Both records occurred at a time when the official readings were taken adjacent to Lake Michigan. 23 of the last 33 lows (70%) were in the: 20s (12) and 30s (11). Six consecutive 20s & 30s lows occurred from 1986 through 1991. Three lows (9%) were in the cold 10s (a.k.a. teens). There were only two 10s lows prior to 1978: 13 in 1964 and 15 in 1969. Seven lows (21%) were in the 40s.

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1983 the high was 58 with a low of 40, overall 11 degrees ABOVE normal. Then in 1984 the high was 37 with a low of 18, overall 10.5 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:19 and sunrise is at 6:50. Sunset is at 16:28 and twilight ends at 16:58. There's a total of 9 hours, 38 minutes of daylight today and 10 hours, 39 minutes between twilights. We lost three minutes of daylight from yesterday. Tomorrow twilight begins at 6:20 and sunrise is at 6:51. The moon is waning crescent, having reached last quarter two mornings ago at 9:09. Illumination was 32% at midnight, will be 27% at noon and 22% at midnight tonight. Moonrise was at 1:12 this morning. Moonset is at 13:21 this afternoon. Moonrise is at 2:25 tomorrow morning. Moonlight time is 12 hours, 9 minutes which is 41 minutes shorter than yesterday.

Cool Fall began November 2 and runs for 29 days through November 30. High temperatures in this period are usually in the 30s, 40s and 50s. Highs in the 10s and 20s occur infrequently. Thanksgiving is in four days.