December 17: ORD

Today is December 17th. It's the 352nd day of the year. 14 days remain. It's week 51 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. Observations have been official at O'Hare since Thursday, January 17, 1980.

According to the National Climatic Data Center (NCDC), the normal high is 34 and the normal low is 20. The 30-year averages are 32 and 19.

On the warm side, two years ago the high was 54 with a low of 41. Five years prior, in 2001, the high was 46 with a low of 33. In 1993 the high was 41 with a low of 36, a five degree spread. Other warm highs were 48 in 1997 and 44 in 1984. Other warm lows were 34 in 1990, 33 in 1986, 32 in 1994 and 30 in 2002. The record high of 60 and record warmest low of 44 occurred on the same day in 1977. 13 of the last 30 highs were 30s. On the warmer side, six highs were 40s and one high was in the 50s. On the colder side, five highs were in the 20s, four highs were 10s and one high was in the single digits.

In looking back through the years to the first December at O'Hare in 1958, the following instances were notable. In 1972 the high was 23 with a low of -5, a cold day. In 1970 the high was 38 with a low of 36, a two degree spread. In 1963 the high was 15 with a low of -9, a cold day. In 1961 the high was 34 with a low of 31, a spread of three degrees.

More recently, we had small spreads of five degrees in 1990 (39/34), six degrees in 1992 (33/27) and seven degrees in the following years: 1982 (32/25), 1986 (40/33), 2002 (37/30) and 2003 (26/19).

On the cold side, in 1985 the high was 13 with a low of -6. Two years prior, in 1983, the high was 9 with a low of 0. In 2000 the high was 16 with a low of -1. In 1989 the high was 16 with a low of 3. In 1979 the high was 19 with a low of 1. In 2005, three years ago, the high was 20 with a low of 11. In 1988 the high was 21 with a low of 10. The record low of -7 was set in 1951 and record coldest high of 8 was set six years earlier in 1945. 24 of the last 30 lows were 10s (11), 20s (7) and 30s (6). Among the colder lows, three were zeros and two were negative zeros. Just one low was a 40s low and that occurred just two years ago.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:45 and sunrise is at 7:17. Chicago's twilight and sunrise times are four minutes earlier. Sunset is at 16:23 and twilight ends at 16:55. Chicago's sunset and end of twilight times are two minutes earlier. There's a total of 9 hours, 6 minutes of daylight today and 10 hours, 10 minutes between twilights. Tomorrow twilight begins at 6:45 and sunrise is at 7:17. The moon is waning gibbous, heading towards the last quarter on Friday at 4:29. Illumination was 73% at midnight, will be 68% at noon and 63% at midnight tonight. Moonset is at 10:58 and moonrise is at 22:35. Moonlight time is 12 hours, 23 minutes today.

Today is a major snow day in O'Hare's history. In 1973, 1.4 inches fell. This was the fifth of eight days of measurable snowfall, part of 17.6 inches that fell. This comprised 94% of the month's total of 18.8 inches.

Christmas Eve is in a week and Christmas Day is in eight days. New Year's Eve is in two weeks and New Year's Day is in 15 days. -Bernie-