Friday, December 30, 2011

December 30: ORD

Today is December 30th. It's the 364th day of the year. One day remains. 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 35 and 20.


On the warm side, in 2002 the high was the near-record high of 60 (O'Hare's only 60s high) with a low of 37. A decade earlier, in 1992, the high was 51 with a low of 39. In 2006 the high was 50 with a low of 40. Two years before that, in 2004, the high was 57 with a low of 31. Last year, in 2010, the high was 46 with a low of 34. The other warm high was 47 in 1979. The other warm lows were 33 in 2005, 32 in 1989, 30 in 1980, 30 in 1986 and 30 in 1991. The record high of 61 and record warmest low of 51 were set way back in 1884, at a time when the official readings were taken adjacent to Lake Michigan. 15 of the past 33 highs (46%) were in the 30s. On the warm side, ten highs (30%) were in the: 40s (6), 50s (3) and 60s (1). Prior to 1992, O'Hare's only 50s high was 57 in 1965. On the cold side, eight highs (24%) were in the: 10s (a.k.a. teens) (2) and 20s (6). O'Hare's coldest high was 7 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 10 with a low of -2, a cold day. In 1973 the high was a cold 14 with a low of 7, a seven degree spread and cold day. In 1972 the high was 48 with a low of 35, a warm day. In 1967 the high was 31 with a low of 25, a six degree spread. In 1965 the high was 57 with a low of 39, a warm day. In 1963 the high was 7 with a low of -12, a cold day. In 1962 the high was a cold 15 with a low of 8, a seven degree spread and cold day. In 1961 the high was 18 with a low of -2, a cold day. In 1959 the high was 27 with a low of 21, a six degree spread. In 1958 the high was 30 with a low of 23, a seven degree spread.

More recently, we had small spreads of one degree in 1989 (33/32), two degrees in 1980 (32/30) and seven degrees in 1991 (37/30). We had a large spread of 34 degrees in 1985 (high of 37, low of 3).

On the cold side, in 1983 the high was the near-record coldest high of 10 with the near-record low of -6. The record coldest high of 9 was set back in 1938 and the record low of -7 was set way back in 1909. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. In 1998 the high was 13 with a low of 1. In 2001 the high was 20 (our most recent 20s high) with a low of 5 (our most recent single digit low). In 1981 the high was 29 with a low of -2. The other cold lows were 3 in 1985, 3 in 1993 and 5 in 1990. 19 of the last 33 lows (58%) were in the: 20s (10) and 30s (9). On the cold side, 13 lows (39%) were in the: negative single digits (2), single digits (5) and 10s (a.k.a. teens) (6). O'Hare's coldest low was -12 in 1963. The other below zero lows were -2 in both 1961 and 1976. On the warm side, one low (3%) was in the 40s.

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 1992 the high was 51 with a low of 39, overall 20 degrees ABOVE normal. Then in 1993 the high was 27 with a low of 3, overall 10 degrees BELOW normal. In the second instance, in 2001 the high was 20 with a low of 5, overall 12.5 degrees BELOW normal. Then in 2002 the high was 60 with a low of 37, overall 23.5 degrees ABOVE normal.

Today is a major snow day in O'Hare's history. Back in 1978, 1.6 inches fell. This was day three of a four day, 16.8 inch storm. The total snowfall of December 1978 was 35.1 inches at O'Hare.

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 16:30 and twilight ends at 17:02. There's a total of 9 hours, 8 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 in two days at 0:15. Illumination was 31% at midnight, will be 36% at noon and 41% at midnight tonight. Moonrise is at 10:34 this morning. Moonset is at 23:13 tonight. Moonrise is at 10:58 tomorrow morning. Moonlight time is 12 hours, 39 minutes which is 36 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 tomorrow. New Year's Day is in two days.