November 21: ORD

Today is November 21st. It's the 325th day of the year. 40 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 45 and the normal low is 30. I've calculated the 33-year averages at 45 and 30.

On the warm side, in 1990 the high was 66 with a low of 49, O'Hare's warmest for the date. In 1979 the high was 60 with a low of 47. Last year, in 2010, the high was 60 with a low of 41. The other warm high was 57 in 1992. The record high of 72 and record warmest low of 62 were set on the same warm day back in 1913, a time when the official readings were taken adjacent to Lake Michigan. 28 of the past 33 highs (85%) were in the: 30s (9), 40s (9) and 50s (10). Three notable stretches of 30s, 40s & 50s highs occurred: 1. ten years from 1980 through 1989, 2. nine years from 1991 through 1999 and 3. seven years from 2001 through 2007. There have been no highs in the 30s following the high of 37 in 1996, but both 20s highs occurred after 1996. Three highs were in the warm 60s. There were two more 60s highs prior to 1978 (62 in 1963 and 61 in 1973). Two highs were in the cold 20s.

In looking back through the years to the first November at O'Hare in 1958, the following instances were notable: in 1976 the high was 36 with a low of 29, a seven degree spread. In 1975 the high was 39 with a low of 33, a six degree spread. In 1974 the high was 38 with a low of 31, a seven degree spread. In 1973 the high was a warm 61 degrees. In 1972 the high was 37 with a low of 31, a six degree spread. In 1970 the high was 55, then a cold front came through and by the 23rd, the low was 10, a 45 degree drop! In 1967 the high was 40 with a low of 33, a seven degree spread. In 1964 the high was just 15 with a low of 5, a cold day. In 1963 the high was 62 with a low of 43, a warm day.

More recently, there were no large spreads. There were small spreads of four degrees in 1988 (35/31), five degrees in 1978 (31/26), and seven degrees in 1996 (37/30).

On the cold side, in 2000 the high was 24 with a low of 14. Three years ago, in 2008, the high was 29 with a low of 17. In 1985 the high was 35 with a low of 13. In 1981 the high was 30 with a low of 20. In 1987 the high was 35 with a low of 16. The other cold low was 16 in 1984. The other cold high was 31 in 1978. The record low of 1 and record coldest high of 11 were set on the same cold day way back in 1880, at a time when the official readings were taken adjacent to Lake Michigan. 16 of the last 33 lows (49%) were in the 30s. 13 lows (39%) were in the cold: 10s (a.k.a. teens) (5) and 20s (8). Four lows (12%) were in the warm 40s. The coldest day for the date is easily 1964. With a high of 15 and low of 5, it's overall 28 degrees below normal. The high is 30 degrees below normal. The low is 25 degrees below normal.

Three of four years from 1984-1987 were very cold. In 1984, it was 11 degrees below normal (38/16). In 1985, it was 14 degrees below normal (35/13). Then 1986 was just slightly below normal (40/30). And 1987 was 12.5 degrees below normal (35/16).

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:20 and sunrise is at 6:51. Sunset is at 16:27 and twilight ends at 16:58. There's a total of 9 hours, 36 minutes of daylight today and 10 hours, 38 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:21 and sunrise is at 6:52. The moon is waning crescent, having reached last quarter three mornings ago at 9:09. Illumination was 22% at midnight, will be 17% at noon and 13% at midnight tonight. Moonrise was at 2:25 this morning. Moonset is at 13:52 this afternoon. Moonrise is at 3:40 tomorrow morning. Moonlight time is 11 hours, 27 minutes which is 42 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 three days.