December 18: ORD

Today is December 18th. It's the 353rd day of the year. 13 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 33 and the normal low is 19. The 30-year averages are 32 and 18.

On the warm side, in 2002 the high was 55 with a low of 37. Four years prior, in 1998, the high was 53 with a low of 32. These are the only highs in the 50s over the past 30 years. In 1997 the high was 46 with a low of 32. Four years later, in 2001, the high was 48 with a low of 29. In 1993 the high was 41 with a low of 35, a six degree spread. In 1982 the high was 43 with a low of 32. Other warm lows were 33 in 1995, 31 in 1978 and 30 in 1990. The record high of 62 and record warmest low of 43 occurred on the same day way back in 1877, exactly a century earlier than yesterday's comparable records. 13 of the last 30 highs were 30s. On the warmer side, six highs were 40s and two highs were in the 50s. On the colder side, three highs were in the 20s, five 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 1977 the high was 42 with a low of 36, a six degree spread. In 1973 the high was 26 with a low of 20, a six degree spread. In 1968 the high was 37 with a low of 32, a five degree spread. In 1964 the high was 18 with a low of 0, a cold day. In 1963 the high was 9 with a low of -9, another cold day. In 1961 the high was 35 with a low of 29, a six degree spread.

More recently, we had a small spread of four degrees in 1995 (37/33), five degrees in 1986 (34/29) and seven degrees 1990 (37/30).

On the cold side, in 1983 the high was the near-record coldest high of 3 with the record low of -11. The record coldest high of one above still stands, set way back in 1884. Two years later, in 1985, the high was 10 with a low of -9. In 2000 the high was 16 with a low of -1. In 1989 the high was 16 with a low of 2. In 2005, three years ago, the high was 15 with a low of 4. In 1996 the high was 18 with a low of 7. Five years before, in 1991, the high was 22 with a low of 7. Other cold lows were 6 in 1999 and 7 in 1981. 27 of the last 30 lows were 0s (6), 10s (7), 20s (6) and 30s (8). Among the colder lows, two were negative zeros and one was a negative 10s low.

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 three minutes earlier. Sunset is at 16:23 and twilight ends at 16:55. Chicago's sunset is a minute earlier and end of twilight time is 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 6:46 and sunrise is at 7:18. The moon is waning gibbous, heading towards the last quarter tomorrow at 4:29. Illumination was 63% at midnight, will be 57% at noon and 52% at midnight tonight. Moonset is at 11:20 and moonrise is at 23:44. Moonlight time is 11 hours, 36 minutes today.

Today is a major snow day in O'Hare's history. In 1973, 0.6 inches fell. This was the sixth 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 six days and Christmas Day is in a week. New Year's Eve is in 13 days and New Year's Day is in two weeks. -Bernie-