December 11: ORD

Today is December 11th. It's the 345th day of the year. 20 days remain. It's week 50 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 36 and the normal low is 22. I've calculated the 33-year averages at 36 and 21.

On the warm side, in 1979 the high was 56 (ties 56 in 1965 as O'Hare's warmest) with a low of 34. In 1990 the high was 55 with a low of 32. In 1987 the high was 48 with a low of 34. In 2006 the high was 45 with a low of 37 (tied with 1959 & 1967 as O'Hare's warmest lows). The other warm highs were 49 in 1991, 49 in 1998 and 48 in 2001. The other warm low was 36 in 1996. The record high of 61 was set back in 1949. The record warmest low of 50 occurred in 1965. Both records were set at Midway. 15 of the past 33 highs (46%) were in the 30s. Ten highs (30%) were in the warm: 40s (8) and 50s (2). Besides a high of 56 in 1965, O'Hare's other pre-1978 very warm high was 51 in 1968. Eight highs (24%) were in the cold: 0s (1), 10s (1) and 20s (6). O'Hare's coldest high was 7 in 1962.

In looking back through the years to the first December at O'Hare in 1958, the following instances were notable: in 1977 the high was 23 with a low of -7, a 30 degree spread and cold day. That low of -7 was colder than the record low of -5 in 1972 at MDW. In 1976 the high was 24 with a low of 5, a cold day. In 1975 the high was 38 with a warm low of 35, a mere three degree spread. In 1972 the high was 21 with a low of -13, a 34 degree spread and cold day. That low of -13 was colder than the record low of -5 in at MDW this same day. In 1970 the high was 40 with a warm low of 35, a five degree spread. In 1968, the high was a warm 51 degrees. In 1967 the high was 40 with a warm low of 37, a three degree spread. In 1965 the high was 56 with a low of 51, a five degree spread and warm day. That low of 51 was warmer than the record warmest low of 50 at MDW this same day. In 1964 the high was 40 with a low of 33, a seven degree spread. In 1963 the high was 30 with a low of 25, a five degree spread. In 1962 the high was 7 with a low of -4, a cold day. That low of -4 is near the record low of -5, set in 1972. 1962 is also the year of the record coldest high of 6 at MDW. In 1959 the high was 43 with a warm low of 37, a six degree spread. In 1958 the high was 21 with a low of 7, a cold day.

More recently, there were no large spreads of 30 degrees or more. There were small spreads of three degrees in 1996 (39/36), three degrees in 1997 (35/32), five degrees in 1983 (38/33), five degrees in 2004 (37/32) and six degrees in 2007 (33/27).

On the cold side, in 1995 the high was 8 with a low of 1, a seven degree spread. In 1988 the high was 18 with a low of 3. Two years ago, in 2009, the high was 23 with a low of 7. In 1982 the high was 26 with a low of 9. In 1980 the high was 24 with a low of 11. The other cold low was 7 in 2005. The other cold high was 24 in 1994. The record low of -5 was set in 1972. The record coldest high of 6 occurred in 1962. Both records were set at Midway. 28 of the last 33 lows (85%) were in the: 10s (a.k.a. teens)(10), 20s (8) and 30s (10). There were consecutive instances of lows in the 10s, 20s and 30s: six years from 1989 through 1994 and nine years from 1996 through 2004. Five lows were in the cold 0s (aka single digits). All of O'Hare's negative lows occurred prior to 1978: -13 in 1972, -7 in 1977 and -4 in 1962.

There were three instances of back-to-back years in which temperatures were just about as opposite as they can be. 1. In 1979 the high was 56 with a low of 34, overall 16 degrees ABOVE normal. Then in 1980 the high was 24 with a low of 11, overall 11.5 degrees BELOW normal. 2. In 1987 the high was 48 with a low of 34, overall 12 degrees ABOVE normal. Then in 1988 the high was 18 with a low of 3, overall 18.5 degrees BELOW normal. 3. In 1989 the high was 27 with a low of 11, overall 10 degrees BELOW normal. Then in 1990 the high was 55 with a low of 32, overall 14.5 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:40 and sunrise is at 7:12. Sunset is at 16:21 and twilight ends at 16:53. There's a total of 9 hours, 9 minutes of daylight today and 10 hours, 13 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 6:41 and sunrise is at 7:13. The moon is waning gibbous, having reached the full Cold or Long Nights moon yesterday at 8:36. Illumination was 100% at midnight, will be 99% at noon and 97% at midnight tonight. Moonset is at 8:00 this morning. Moonrise is at 17:32 this afternoon. Moonset is at 8:44 tomorrow morning. Moonlight time is 14 hours, 28 minutes which is 8 minutes shorter than yesterday. Moonlight time is at it's peak, just when it is full. It doesn't get any better than this!

Winter began December 1st and runs for 102 days through March 11th. High temperatures in this period are usually in the 20s and 30s. Highs in the 40s and 50s occur infrequently. Bill of Rights Day is in four days.