November 21: ORD

Today is November 21st. It's the 326th 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. From Friday, January 1, 1926 through Tuesday, June 30, 1942, the official site was at the University of Chicago. 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 34-year averages at 45 and 30.

On the warm side, in 1990 (O'Hare's warmest November 21st) the high was 66 (O'Hare's warmest high of the date) with a low of 49 (O'Hare's warmest low of the date). In 1979 (O'Hare's second warmest November 21st) the high was 60 with a low of 47 (O'Hare's second warmest low of the date). Two years ago, in 2010, the high was 60 with a low of 41. The other warm highs were 61 degrees in 1973 and 57 degrees in 1992. The record high of 72 degrees and record warmest low of 62 degrees were set on the same warm day back in 1913, at a time when the official readings were taken adjacent to Lake Michigan. 29 of the past 34 highs (85%) were in the: 30s (9), 40s (10) and 50s (10). There have been no highs in the 30s following the high of 37 degrees in 1996, but both 20s highs occurred after 1996! Three highs were in the warm 60s. Two highs were in the cold 20s. The other warm day was in 1963 as the high was 62 (O'Hare's second warmest high of the date) with a low of 43. There have been no highs of 70 degrees or higher or lows of 50 degrees or higher on November 21st in O'Hare's history.

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), six degrees last year, in 2011 (47/41) and seven degrees in 1996 (37/30). 

On the cool side, in 2000 (O'Hare's second coolest November 21st) the high was 24 (O'Hare's second coolest high of the date) with a low of 14 (O'Hare's third coldest low of the date). In 2008 the high was 29 with a low of 17. In 1985 the high was 35 with a low of 13 (O'Hare's second coldest low of the date). 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 degrees in 1984. The other cool high was 31 degrees in 1978. The record low of 1 degree and record coolest high of 11 degrees 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 34 lows (47%) were in the 30s. 13 lows (38%) were in the cold: 10s (a.k.a. teens) (5) and 20s (8). Five lows (15%) were in the warm 40s. O'Hare's coolest November 21st was in 1964 as the high was 15 (O'Hare's coolest high and only 10s (a.k.a. teens) high and low of 5 (O'Hare's coldest and only single digit low of the date), overall 28 degrees below normal. The high is 30 degrees below normal and the low is 25 degrees below normal!

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:21 and sunrise is at 6:52. Sunset is at 16:27 and twilight ends at 16:57. There's a total of 9 hours, 35 minutes of daylight today and 10 hours, 36 minutes between twilights. We lost one minute of daylight from yesterday. Tomorrow twilight begins at 6:22 and sunrise is at 6:53. The moon is waxing gibbous, having reached first quarter yesterday at 8:31. Illumination was 57% at midnight, will be 62% at noon and 67% at midnight tonight. Moonset was at 0:03 this morning. Moonrise is at 12:48 this afternoon. Moonset is at 1:06 tomorrow morning. Moonlight time is 11 hours, 15 minutes which is 25 minutes shorter than yesterday.

Cool Fall began on November 2nd and runs for 29 days through November 30th. High temperatures in this period are usually in the 30s, 40s and 50s. Highs in the 20s, 60s and 70s occur infrequently. Thanksgiving is tomorrow. Pearl Harbor Day is in 16 days.