December 6: ORD

Today is December 6th. It's the 340th day of the year. 25 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 38 and the normal low is 24. I've calculated the 33-year averages at 37 and 23.

On the warm side, in 1980 the high was the record high of 65 with the record warmest low of 52. The record high of 65 was first set in 1951. In 1998 the high was 62 (our most recent 60s high) with a low of 37. In 2004 the high was 50 (our most recent 50s high) with a low of 40. Three years prior, in 2001, the high was 51 with a low of 37. The other warm high was 53 in 1988. 16 of the past 33 highs (49%) were in the 30s. 11 highs (33%) were in the warm: 40s (6), 50s (3) and 60s (2). There were two periods of 40s highs. The first one was three instances from 1979 through 1982. The second one was three instances from 1989 through 1993. Our most recent 40s high was 41 in 1993. The two 60s highs are the only ones in ORD history. Prior to 1978, the warmest high was 56 in 1966. Six highs (18%) were in the cold: 10s (a.k.a. teens)(1) and 20s (5). Prior to 1978, the cold highs were 17 in 1958 and 18 in 1964.

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 28 with a cold low of -1, a cold day. That low of -1 was colder than the record low of zero in 2007. In 1973 the high was 32 with a low of 25, a seven degree spread. In 1972 the high was 24 with a low of 0, a cold day. In 1971 the high was 43 with a warm low of 38, a five degree spread. In 1970 the high was 28 with a cold low of 11, a cold day. In 1967 the high was 46 with a warm low of 42, a four degree spread and warm day. In 1966 the high was 56 with a low of 39, a warm day. In 1964 the high was 18 with a low of -3, a cold day. That low of -3 was colder than the record low of zero in 2007. In 1962 the high was 29 with a low of 25, a four degree spread. In 1959 the high was 31 with a low of 26, a five degree spread. In 1958 the high was 17 with a low of 5, a cold day. That high of 17 was just a degree above the record coldest high of 16 in 1893.

More recently, there was a large spread of 35 degrees in 1991 (41/6). There were small spreads of five degrees in 1994 (38/33), seven degrees in 1997 (32/25) and seven degrees in 2003 (37/30).

On the cold side, in 2005 the high was 17 with a low of 4. Two years later, in 2007, the high was 24 with the record low of 0. The record low of 0 also occurred previously in 1972 and originally way back in 1885. Last year, in 2010, the high was 20 with a low of 8. In 1984 the high was 21 with a low of 8. In 2000 the high was 20 with a low of 10. The other cold lows were 6 in 1991 and 9 in 2002. The record coldest high of 16 was set way back in 1893, at a time when the official readings were taken adjacent to Lake Michigan. 31 of the last 33 lows (94%) were in the: 0s (6), 10s (a.k.a. teens)(7), 20s (11) and 30s (7). The coldest pre-1978 lows were: -3 in 1964, -1 in 1977, 0 in 1972 and 5 in 1958. There were two three-year strings of lows in the 20s: first, from 1985-1987 and second, from 1995-1997. Our most recent 30s low was 30 in 2003. Two lows were in the warm: 40s (1) and 50s (1). The warmest pre-1978 low was 42 in 1967.

There were two instances of back-to-back years in which temperatures were just about as opposite as they can be. First instance: in 2000 the high was 20 with a low of 10, overall 16 degrees BELOW normal. Then in 2001 the high was 51 with a low of 37, overall 13 degrees ABOVE normal. Second instance: in 2004 the high was 50 with a low of 40, overall 14 degrees ABOVE normal. Then in 2005 the high was 17 with a low of 4, overall 20.5 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:36 and sunrise is at 7:07. Sunset is at 16:21 and twilight ends at 16:53. There's a total of 9 hours, 14 minutes of daylight today and 10 hours, 17 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 6:37 and sunrise is at 7:08. The moon is waxing gibbous. Illumination was 83% at midnight, will be 87% at noon and 90% at midnight tonight. Moonset is at 3:23 this morning. Moonrise is at 13:50 this afternoon. Moonset is at 4:22 tomorrow morning. Moonlight time is 13 hours, 33 minutes which is 31 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 tomorrow. Bill of Rights Day is in nine days.