December 17: ORD

Today is December 17th. It's the 351st 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. ORD has been the official site of record for Chicago since Thursday, January 17, 1980.

According to the National Climatic Data Center (NCDC), the normal high is 34 and the normal low is 20. I've calculated the 32-year averages at 31 and 19.

On the warm side, in 2006 the high was 54 with a low of 41 (our only 50s high and only 40s low). Five years prior, in 2001, the high was 46 (our most recent 40s high) with a low of 33. In 1993 the high was 41 with a low of 36, a five degree spread. Another warm high was 48 in 1997. Other warm lows were 34 in 1990, 33 in 1986 and 32 in 1994. The record high of 60 and record warmest low of 44 were set on the same day in 1977 at Midway. Over the last 32 years, 14 highs (44%) were in the 30s. Seven highs (22%) were in the warmer: 40s (6) and 50s (1). 11 highs (34%) were in the cold: 0s (aka single digits)(1), 10s (aka teens)(4) and 20s (6).

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 56 with a low of 41, a warm day and year of both the record high and record warmest low. In 1975 the high was 20 with a low of 8, a cold day. In 1973 the low was a cold 7 degrees. In 1972 the high was 23 with a cold low of -5, a cold day. In 1970 the high was 38 with a warm low of 36, a mere two degree spread. In 1966 the low was a warm 32. In 1964 the high was 24 with a cold low of 2, a cold day. In 1963 the high was 15 with a low of -9, a cold day. In 1962 the high was a warm 50. In 1961 the high was 34 with a low of 31, a three degree spread.

More recently, there were no large spreads of 30 degrees or more. There were small spreads of five degrees in 1990 (39/34), six degrees in 1992 (33/27) and seven degrees in four 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. Two years ago the high was 20 with a low of 6. In 2005 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. The record coldest high of 8 was set in 1945. 25 of the last 32 lows (78%) were: 10s (aka teens)(12), 20s (7) and 30s (6). Our most recent 30s low was 30 in 2002. Six lows were in the cold: negative 0s (2) and 0s (aka single digits)(4). One low was in the warmer 40s.

In 1973, O'Hare had 1.4 inches of snow today. This was the fifth day of a string of eight days through the 20th which produced 17.6 inches, or 94% of the month's total of 18.8 inches.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:45 and sunrise is at 7:16. Sunset is at 16:23 and twilight ends at 16:54. There's a total of 9 hours, 7 minutes of daylight today and 10 hours, 9 minutes between twilights. We are losing a minute of daylight per day. Tomorrow twilight begins at 6:45 and sunrise is at 7:17. The moon is waxing gibbous. Illumination was 83% at midnight, will be 86% at noon and 89% at midnight tonight. Moonset is at 3:33 this morning. Moonrise is at 13:30 this afternoon. Moonset is at 4:38 tomorrow morning. Moonlight time is 14 hours, 3 minutes which is 41 minutes longer than yesterday.

Christmas Eve is in seven days and Christmas Day is in eight days. -Bernie-