December 24: ORD

Today is December 24th. It's the 358th day of the year. Seven days remain. It's week 52 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. 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 33 and the normal low is 19. I've calculated the 33-year averages at 30 and 15.

On the warm side, in 1982 the high was the near-record high of 62 (O'Hare's only 60s high of the date) with the record warmest low of 51. The record high of 64 was set way back in 1889, at a time when the official readings were taken adjacent to Lake Michigan. In 1979 the high was 51 (one of only two 50s highs in O'Hare's history for the date) with a low of 37. In 1987 the high was 48 with a low of 34. The other warm lows were 34 in 2005, 33 in 1997 and 32 two years ago, in 2009. 20 of the past 33 highs (61%) were in the: 20s (10) and 30s (10). On the warm side, seven highs (21%) were in the: 40s (5), 50s (1) and 60s (1). Our most recent 40s high was 44 in 2006. O'Hare's only other 50s high was 50 in 1965. On the cold side, six highs (18%) were in the negative 10s (a.k.a. negative teens) (1) and 10s (a.k.a. teens) (5).

In looking back through the years to the first December at O'Hare in 1958, the following instances were notable. In 1976 the high was 40 with a cold low of 7, a 33 degree spread. In 1975 the high was 34 with a low of 28, a six degree spread. In 1973 the high was 38 with a warm low of 32, a six degree spread. In 1972 the high was 35 with a warm low of 31, a four degree spread. In 1971 the high was a warm 45 degrees. In 1968 the high was 16 with a low of 5, a cold day. In 1966 the low was a cold 5 degrees. In 1965 the high was 50 with a low of 34, a warm day. In 1964 the high was a warm 47 degrees. In 1963 the low was a cold 4 degrees. In 1962 the high was 19 with a low of -4, a cold day.

More recently, we had a large spread of 30 degrees in 1980 (32/2). We also had small spreads of two degrees in 1997 (35/33), four degrees two years ago, in 2009 (36/32), five degrees in 2005 (39/34), five degrees last year, in 2010 (32/27), six degrees in 1993 (18/12), six degrees in 1995 (28/22), six degrees in 2001 (21/15) and six degrees in 2007 (26/20).

On the cold side, in 1983 the high was the record coldest high of -11 with the record low of -25. Six years later, in 1989, the high was 14 with a low of -6. In 2000 the high was 11 with a low of -2. Four years later, in 2004, the high was 12 with a low of -2. In 1985 the high was 22 with a low of -8. Five years later, in 1990, the high was 16 with a low of 1. Two years later, in 1992, the high was 22 with a low of -3. In 1999 the high was 20 with a low of 8. In 1984 the high was 28 with a low of 0. The other cold lows were 2 in 1980, 6 three years ago in 2008 and 7 in 1996. The other cold highs were 18 in 1993 and 21 in 2001. 21 of the last 33 lows (64%) were in the: single digits (6), 10s (a.k.a. teens) (6) and 20s (9). Our most recent 10s low was 17 in 2003. On the cold side, six lows (18%) were in the: negative 20s (1) and negative single digits (5). Prior to 1983, O'Hare's only negative low was -4 in 1962. On the warm side, six lows (18%) were in the: 30s (5) and 50s (1). O'Hare has never had a low in the 40s for the date.

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1982 the high was 62 with a low of 51, overall 30.5 degrees ABOVE normal. Then in 1983 the high was -11 with a low of -25, overall 44 degrees BELOW normal.

Today is a major snow day in O'Hare's history. In 1969, 2.1 inches fell. This was the fourth of four days of measurable snowfall, part of a total of 13.5 inches during the period.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:48 and sunrise is at 7:20. Sunset is at 16:26 and twilight ends at 16:58. There's a total of 9 hours, 6 minutes of daylight today and 10 hours, 10 minutes between twilights. We gained a minute of daylight from yesterday. Tomorrow twilight begins at 6:49 and sunrise is at 7:20. The moon reaches new today at 12:06. Illumination was 0% at midnight, will be 0% at noon and 0% at midnight tonight. Moonrise is at 7:08 this morning. Moonset is at 16:39 this afternoon. Moonrise is at 7:57 tomorrow morning. Moonlight time is 9 hours, 31 minutes which is 7 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. Christmas Eve is today. Christmas is tomorrow.