December 10: ORD

Today is December 10th. It's the 344th day of the year. 21 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 37 and 22.

On the warm side, in 1979 the high was 56 (the warmest of the past 33 years) with a low of 31. In 2003 the high was 53 with a low of 29. A year later, in 2004, the high was 45 with a low of 37. The other warm highs were 51 in 1993, 49 in 1991, 48 in 1990 and 48 in 2001. The record high of 62 was set way back in 1879. The record warmest low of 46 occurred way back in 1911. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 24 of the past 33 highs (73%) were in the: 30s (14) and 40s (10). There were the following consecutive highs in the 30s & 40s: six years from 1980 through 1985 and seven years from 1996 through 2002. Three highs were in the warm 50s. O'Hare's warmest high was 57 in 1971. The other pre-1978 warm high was 51 in 1965. Six highs were in the cold: 10s (a.k.a. teens) (2) and 20s (4). O'Hare's coldest high was 8 in 1977.

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 8 with a low of -7, a cold day. That high of 8 is equal to the official record coldest high set in 1919. In 1976 the high was 40 with a cold low of 7, a 33 degree spread. In 1973 the high was a cold 23 with a low of 12, a cold day. In 1972 the high was 15 with a low of -6, a cold day. In 1971 the high was 57 with a low of 36, a warm day. In 1967 the high was 38 with a warm low of 36, a two degree spread. In 1965 the high was a warm 51 with a low of 33, a warm day. In 1962 the high was 18 with a low of 4, a cold day. In 1958 the high was 12 with a low of -8, a cold day. That low of -8 is equal to the official record low set in 1978 at MDW.

More recently, there were no other large spreads of 30 degrees or more. There were small spreads of three degrees in 1997 (36/33), four degrees in 1992 (34/30), seven degrees in 1985 (37/30) and seven degrees in 2007 (32/25).

On the cold side, in 1978 the high was 21 with a low of -10 (O'Hare's coldest), a 31 degree spread. Two years ago, in 2009, the high was 13 with a low of 0. In 1995 the high was 14 with a low of 0. In 1986 the high was 20 with a low of 9. The other cold lows were 8 in 1988 and 9 in 1983. The record low of -8 was set in 1978 at Midway. The record coldest high of 8 and original record low of -8 were set in 1919, a time when the official readings were taken adjacent to Lake Michigan. 23 of the last 33 lows (70%) were in the: 20s (13) and 30s (10). There were the following consecutive lows in the 20s & 30s: six from 1989 through 1994 and nine from 1996 through 2004. Ten lows were in the cold: negative 10s (1), 0s (5) and 10s (4). There's been an absence of lows in the negative 0s. O'Hare's cold lows prior to 1978 were -8 in 1958 (ties the official record low), -7 in 1977 and -6 in 1972.

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1978 the high was 21 with a low of -10, overall 23.5 degrees BELOW normal. Then in 1979 the high was 56 with a low of 31, overall 14.5 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:39 and sunrise is at 7:11. Sunset is at 16:21 and twilight ends at 16:53. There's a total of 9 hours, 10 minutes of daylight today and 10 hours, 14 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 6:40 and sunrise is at 7:12. The moon is waxing gibbous and reaches the full Cold or Long Nights moon today at 8:36. Illumination was 100% at midnight, will be 100% at noon and 100% at midnight tonight. Moonset is at 7:11 this morning. Moonrise is at 16:35 this afternoon. Moonset is at 8:00 tomorrow morning. Moonlight time is 14 hours, 36 minutes which is 4 minutes longer 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 five days.