December 7: ORD

Today is December 7th. It's the 341st day of the year. 24 days remain. It's week 49 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 37 and the normal low is 23. I've calculated the 33-year averages at 36 and 24.

On the warm side, in 1980 the high was 59 with the record warmest low of 45. Both the high and low are O'Hare's warmest for the date. In 2004 the high was 50 with a low of 41 (our most recent 50s high and 40s low). In 1981 the high was 52 with a low of 38. A decade later, in 1991, the high was 49 with a low of 39. The other warm low was 35 in 2001. The record high of 64 was set in 1916, at a time when the official readings were taken adjacent to Lake Michigan. 23 of the past 33 highs (70%) were in the: 30s (13) and 40s (10). There were 14 consecutive 30s & 40s highs from 1990 through 2003. Our most recent 40s high was 41 in 2003. Three highs (9%) were in the warm 50s. The pre-1978 warm highs were 56 in 1963 and 51 in 1967. Seven highs (21%) were in the cold: 10s (2) and 20s (5). Four of these cold highs occurred from 2005-2010 and the other three occurred from 1983-1989. Prior to 1978, the cold highs were 14 in 1958, 15 in 1977 and 19 in 1976.

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 15 with a low of -1, a cold day. In 1976 the high was 19 with a low of 3, a cold day. In 1974 the high was 40 with a warm low of 35, a five degree spread. In 1972 the high was 22 with a low of -2, a cold day. In 1971 the high was 44 with a warm low of 40, a four degree spread and warm day. In 1969 the high was 37 with a low of 33, a four degree spread. In 1967 the high was 51 with a low of 39, a warm day. In 1966 the high was 46 with a warm low of 40, a six degree spread and warm day. In 1963 the high was a warm 56 with a low of 22, a 34 degree spread. In 1958 the high was 14 with a low of 5, a cold day.

More recently, there were no large spreads of 30 degrees or more. There were small spreads of two degrees in 1997 (31/29), four degrees in 1982 (36/32), four degrees in 1986 (38/34), five degrees two years ago in 2009 (31/26), six degrees in 2007 (30/24) and seven degrees in 1992 (30/23).

On the cold side, in 2005 the high was 15 with a low of 0. Three years later and also three years ago in 2008, the high was 20 with a low of 4. Two years earlier, in 2006, the high was 17 with a low of 9. Last year, in 2010, the high was 20 with a low of 11. In 1984 the high was 27 with a low of 7. In 1989 the high was 23 with a low of 12. So four of the six cold years occurred recently. The record low of -6 and record coldest high of 6 were set on the same cold day way back in 1882, at a time when the official readings were taken adjacent to Lake Michigan. 22 of the last 33 lows (67%) were in the: 20s (14) and 30s (8). There were eight consecutive 20s & 30s lows from 1996 through 2003. Nine lows (27%) were in the cold: 0s (4) and 10s (5). The pre-1978 cold lows were -2 in 1972, -1 in 1977, 3 in 1976 and 5 in 1958. Two lows (6%) were in the warm 40s. Our most recent 30s low was 35 in 2001. The pre-1978 warm lows were both 40 degrees, in 1966 and 1971.

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 2004 the high was 50 with a low of 41, overall 15.5 degrees ABOVE normal. Then in 2005 the high was 15 with a low of 0, overall 22.5 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:37 and sunrise is at 7:08. Sunset is at 16:21 and twilight ends at 16:53. There's a total of 9 hours, 13 minutes of daylight today and 10 hours, 16 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 6:38 and sunrise is at 7:09. The moon is waxing gibbous. Illumination was 90% at midnight, will be 93% at noon and 95% at midnight tonight. Moonset is at 4:22 this morning. Moonrise is at 14:23 this afternoon. Moonset is at 5:20 tomorrow morning. Moonlight time is 13 hours, 59 minutes which is 26 minutes longer than yesterday.

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. Pearl Harbor Day is today. Bill of Rights Day is in eight days.