December 29: ORD

Today is December 29th. It's the 363rd day of the year. Two 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 32 and the normal low is 18. I've calculated the 33-year averages at 34 and 20.

On the warm side, in 1984 the high was the record high of 63 with a low of 28, a 35 degree spread. In 2006 the high was 50 with a low of 40 (O'Hare's only 40s low). In 1992 the high was 44 with a low of 39, a five degree spread. In 2003 the high was 47 with a low of 30. In 1979 the high was 52 with a low of 22, a 30 degree spread. The other warm high was 45 in 1999. The other warm lows were 32 in 1989, 32 in 2005, 31 in 1994 and 30 in 1991. The record warmest low of 42 was set way back in 1884, at a time when the official readings were taken adjacent to Lake Michigan. 14 of the past 33 highs (43%) were in the 30s. On the warm side, ten highs (30%) were in the: 40s (7), 50s (2) and 60s (1). Prior to 1979, O'Hare had no highs in the 50s or 60s. On the cold side, nine highs (27%) were in the: single digits (1), 10s (a.k.a. teens) (3) and 20s (5). Prior to 1983, O'Hare had cold highs of 7 in 1976 and 8 in 1963.

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 7 with a low of -7, a cold day. In 1974 the high was 38 with a warm low of 34, a four degree spread. In 1972 the high was 44 with a low of 34, a warm day. In 1969 the high was 30 with a low of 27, a three degree spread. In 1967 the low was a cold 4 degrees. In 1965 the high was 41 with a low of 33, a warm day. In 1964 the high was 44 with a low of 31, a warm day. In 1963 the high was 8 with a low of -8, a cold day. In 1962 the high was 34 with a cold low of 2, a 32 degree spread. In 1961 the high was 14 with a low of 1, a cold day.

More recently, we had a small spread of four degrees in 1986 (33/29), five degrees in 1991 (35/30), five degrees in 2005 (37/32), six degrees in 1989 (38/32), seven degrees in 1980 (36/29), seven degrees in 1982 (24/17) and seven degrees in 1994 (38/31).

On the cold side, in 1983 the high was the record coldest high of 2 with a low of -8. A couple of years earlier, in 1981, the high was 18 with a low of -1. Four years later, in 1985, the high was 18 with a low of 7. In 2001 the high was 19 with a low of 8. In 1988 the high was 20 with a low of 7. The record low of -15 was set way back in 1880, at a time when the official readings were taken adjacent to Lake Michigan. 13 of the last 33 lows (40%) were in the 30s. On the cold side, 13 lows (39%) were in the: negative single digits (2), single digits (7) and 10s (a.k.a. teens) (4). O'Hare had lows of -8 in 1963 (ties -8 in 1983 as O'Hare's coldest) and -7 in 1976. On the warm side, seven lows (21%) were in the: 30s (6) and 40s (1).

There were two instances of back-to-back years in which temperatures were just about as opposite as they can be. In the first instance, in 1983 the high was 2 with a low of -8, overall 28 degrees BELOW normal. Then in 1984 the high was 63 with a low of 28, overall 20.5 degrees ABOVE normal. Then in 1985 the high was 18 with a low of 7, overall 12.5 degrees BELOW normal. In the second instance, in 1988 the high was 20 with a low of 7, overall 11.5 degrees BELOW normal. Then in 1989 the high was 38 with a low of 32, overall 10 degrees ABOVE normal.

Today is a major snow day in O'Hare's history. Back in 1978, 2.3 inches fell. This was day two of a four day, 16.8 inch storm.

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 16:29 and twilight ends at 17:01. There's a total of 9 hours, 7 minutes of daylight today and 10 hours, 11 minutes between twilights. Daylight time remained unchanged from yesterday. Tomorrow twilight begins at 6:50 and sunrise is at 7:22. The moon is waxing crescent. Illumination was 22% at midnight, will be 27% at noon and 31% at midnight tonight. Moonrise is at 10:09 this morning. Moonset is at 22:12 tonight. Moonrise is at 10:34 tomorrow morning. Moonlight time is 12 hours, 3 minutes which is 35 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 in two days. New Year's Day is in three days.