December 31: ORD

Today is December 31st. It's the 365th day of the year. It's the last day of the year. 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 32 and the normal low is 17. I've calculated the 33-year averages at 35 and 21.

On the warm side, in 2006 the high was 56 with the record warmest low of 43 (tied 1933 as the record warmest low). Last year, in 2010, the high was 53 with a low of 41. In 2004 the high was 56 with a low of 29. The two highs of 56 were the warmest at O'Hare since 1965 when the high was 58, O'Hare's warmest. The other warm high was 44 in 1979. The other warm lows were 32 (1980, 1995, 2005), 31 (1984, 1991), 30 in 1986 and 28 in 1989. The record high of 68 was set way back in 1875, at a time when the official readings were taken adjacent to Lake Michigan. 19 of the past 33 highs (58%) were in the 30s. On the warm side, seven highs (21%) were in the: 40s (4) and 50s (3). On the cold side, seven highs (21%) were in the: 10s (a.k.a. teens) (2) and 20s (5). O'Hare's coldest high was 6 in 1976.

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 33 with a warm low of 30, a three degree spread. In 1976 the high was 6 with a low of -8, a cold day. 1976 had the record coolest high (5 at Midway). In 1974 the high was 36 with a warm low of 34, a two degree spread. In 1973 the high was 14 with a low of 2, a cold day. In 1968 the high was 15 with a low of -9, a cold day. In 1967 the high was 25 with a cold low of -11, a 36 degree spread and cold day. That low of -11 was colder than the record low of -10 set the same day at Midway. In 1965 the high was 58 with a low of 30, a warm day. In 1963 the high was 17 with a low of -14, a 31 degree spread and cold day. That low of -14 was also colder than the record low. In 1961 the low was a cold 1 degree. In 1958 the high was 30 with a low of 24, a six degree spread.

More recently, we had small spreads of two degrees in 1980 (34/32), three degrees in 1991 (34/31), four degrees in 1995 (36/32), five degrees in 1984 (36/31), five degrees in 1989 (33/28) and six degrees in 1986 (36/30). We've had one large spread. It turned out to be a normal day. In 1987 the spread was 32 degrees as the high was 39 with a low of 7.

On the cold side, in 1990 the high was 16 with a low of 1. In 1998 the high was 17 with a low of 9. In 1983 the high was 20 with a low of 6. The record low of -10 was set in 1967 at Midway (it was -11 at O'Hare). O'Hare's coldest reading was -14 in 1963. The record coldest high of 5 was set in 1976 at Midway. 13 of the last 33 lows (40%) were in the 20s. On the cold side, 12 lows (36%) were in the: single digits (8) and 10s (a.k.a. teens) (4). O'Hare's other negative lows were -9 in 1968 and -8 in 1976. On the warm side, eight lows (24%) were in the: 30s (6) and 40s (2).

Today is a major snow day in O'Hare's history. Back in 1978, 10.1 inches fell. This was day four of a four day, 16.8 inch storm. The total snowfall of December 1978 was 35.3 inches at O'Hare. The Winter of 1978-79 was the snowiest ever, producing 80.6 inches.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:50 and sunrise is at 7:22 (the latest sunrise of the year). Sunset is at 16:31 and twilight ends at 17:02. There's a total of 9 hours, 9 minutes of daylight today and 10 hours, 12 minutes between twilights. We gained a minute of daylight from yesterday. Tomorrow twilight begins at 6:50 and sunrise is at 7:22. The moon is waxing crescent and will reach first quarter tomorrow at 0:15. Illumination was 41% at midnight, will be 45% at noon and 50% at midnight tonight. Moonrise is at 10:58 this morning. Moonset is at 0:12 tomorrow morning. Moonrise is at 11:24 tomorrow morning. Moonlight time is 13 hours, 2 minutes which is 23 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. New Year's Eve is today. New Year's Day is tomorrow.