December 4: ORD

Today is December 4th. It's the 338th day of the year. 27 days remain. It's week 49 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. ORD has been the official site of record for Chicago 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 39 and the normal low is 24. I've calculated the 33-year averages at 37 and 25.

On the warm side, in 1998 the high was the record high of 66 with the record warmest low of 56. Three years later, in 2001, the high was 62 (our most recent 60s high) with a low of 54. Two years prior, in 1999, the high was 54 (our most recent 50s high) with a low of 44 (our most recent 40s low). Five years before, in 1994, the high was 56 with a low of 39. In 1982 the high was 47 with a low of 38. 28 of the past 33 highs (85%) were in the: 20s (7), 30s (13) and 40s (8). For 15 consecutive years, from 1976 through 1990 and nine consecutive years, from 2002 through last year, 2010, highs were in the 20s, 30s and 40s. Our most recent 40s high was 42 in 2004. Four highs were in the warm: 50s (2) and 60s (2). These warm 50s and 60s occurred in four of the eight years from 1994 through 2001. The only 60s high, pre-1978, was 62 in 1961. One high was in the cold 10s (a.k.a. teens).

In looking back through the years to the first December at O'Hare in 1958, the following instances were notable: in 1977 the low was a cold 12 degrees. In 1976 the high was 21 with a low of 6, a cold day. In 1975 the high was a warm 53 degrees. In 1973 the high was 58 with a low of 42, a warm day. In 1971 the high was 41 with a low of 34, a seven degree spread. In 1968 the high was 41 with a low of 35, a six degree spread. In 1965 the high was 38 with a low of 32, a six degree spread. In 1963 the low was a cold 10 degrees. In 1962 the high was a warm 52 with a low of 35, a warm day. In 1961 the high was a warm 62 with a low of 31, a 31 degree spread and warm day. In 1960 the high was 58 with a low of 45, a warm day. In 1959 the high was 49 with a warm low of 37, a warm day.

More recently, there were no large spreads. There were small spreads of five degrees in 1983 (37/32), five degrees in 2003 (39/34), five degrees two years ago, in 2009 (28/23) and six degrees in 1997 (35/29).

On the cold side, in 1991 the high was the record coldest high of 13 (the former record coldest high of 18 occurred way back in 1895) with a low of 3. In 2006 the high was 26 with a low of 6. Three years ago, in 2008, the high was 22 with a low of 12. In 1984 the high was 24 with a low of 12. In 2002 the high was 28 with a low of 10. The other cold lows were 8 in 1978 and 12 in 2005. The other cold high was 27 in 1990. The record low of 0 was set way back in 1893, at a time when the official readings were taken adjacent to Lake Michigan. 22 of the last 33 lows (67%) were in the: 10s (8) and 20s (14). There were seven consecutive 10s & 20s lows from 1984 through 1990. Three lows (9%) were in the cold 0s. Pre-1978, we had a low of 6 in 1976. Eight lows (24%) were in the warm: 30s (5), 40s (1) and 50s (2). Three of the four years from 1998 through 2001 had warm lows in the 40s & 50s. Our most recent 30s low was 34 in 2003.

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 2001 the high was 62 with a low of 54, overall 27 degrees ABOVE normal. Then in 2002 the high was 28 with a low of 10, overall 12 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:34 and sunrise is at 7:05. Sunset is at 16:21 and twilight ends at 16:53. There's a total of 9 hours, 16 minutes of daylight today and 10 hours, 19 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:35 and sunrise is at 7:06. The moon is waxing gibbous, having reached first quarter two days ago at 3:52. Illumination was 67% at midnight, will be 72% at noon and 76% at midnight tonight. Moonset is at 1:25 this morning. Moonrise is at 12:56 this afternoon. Moonset is at 2:24 tomorrow morning. Moonlight time is 12 hours, 29 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. Pearl Harbor Day is in three days. Bill of Rights Day is in 11 days.