December 12: ORD

Today is December 12th. It's the 346th day of the year. 19 days remain. It's week 50 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 35 and the normal low is 21. I've calculated the 33-year averages at 36 and 21.

On the warm side, in 1991 the high was 60 (O'Hare's warmest) with a low of 38. The year earlier, 1990, the high was 55 with a low of 35. Most recently, in 2006, the high was 50 with a low of 38. Five years prior, in 2001, the high was 47 with a low of 38. In 1984 the high was 47 with a low of 32. The other warm highs were 48 in both 1980 and 1998. The other warm low was 35 in 1996. The record high of 61 was set way back in 1877, at a time when the official readings were taken adjacent to Lake Michigan. The record warmest low of 48 occurred in 1968 at Midway. 28 of the past 33 highs (85%) were in the: 20s (9), 30s (10) and 40s (9). Of those categories, the 40s occurred longest ago (44 in 2004). Three highs were in the warm: 50s (2) and 60s (1). The 50s highs, pre-1978 were 57 in 1965 and 53 in 1968. Two highs were in the cold 10s (a.k.a. teens). The two pre-1978 cold highs were 10 degrees in 1962 (ORD's coldest) and 12 degrees in 1958. Both of these highs were colder than the coldest highs of the past 33 years: 15 in 2000 and 17 in 1989.

In looking back through the years to the first December at O'Hare in 1958, the following instances were notable: in 1976 the low was a cold 9 degrees. In 1975 the high was 38 with a warm low of 35, a mere three degree spread. Also in 1975, the temperatures yesterday and today were duplicates! In 1974 the high was 35 with a low of 31, a four degree spread. In 1970 the high was 36 with a low of 32, a four degree spread. In 1968 the high was 53 with a low of 48, a five degree spread and warm day. That low of 48 ties the record warmest low set at MDW on the same day. In 1967 the high was 42 with a warm low of 36, a six degree spread. In 1966 the high was 28 with a low of 21, a seven degree spread. In 1965 the high was 57 with a low of 44, a warm day. In 1964 the low was a warm 33 degrees. In 1963 the low was a cold 8 degrees. In 1962 the high was just 10 degrees (equaling the record coldest high set at MDW on the same day) with a low of -7, a reading near the record low (of -8 in 2000) and a very cold day. In 1961 the low was a cold 7 degrees. In 1960 the high was a cold 23 degrees. In 1959 the high was 39 with a warm low of 34, a five degree spread. In 1958 the high was 12 with a low of 3, a very cold day.

More recently, there were no large spreads of 30 degrees or more. There were small spreads of five degrees in 1983 (36/31), five degrees in 1996 (40/35) and seven degrees in 1987 (39/32).

On the cold side, in 2000 the high was 15 with the record low of -8 (ORD's coldest). In 1989 the high was 17 with a low of 5. Three years before, in 1986, the high was 21 with a low of 5. Four years before that, in 1982, the high was 23 with a low of 7. In 1995 the high was 24 with a low of 7. A decade earlier, in 1985, the high was 22 with a low of 9. Three years ago, in 2008, the high was 21 with a low of 11. The other cold low was 9 in 2005. The record coldest high of 10 occurred in 1962 at Midway. The former record low of -7 also occurred in 1962 at Midway. 19 of the last 33 lows (58%) were in the: 20s (9) and 30s (10). 14 lows (42%) were in the cold: negative 0s (a.k.a. negative single digits)(1), 0s (a.k.a. single digits)(6) and 10s (a.k.a teens)(7). O'Hare's only 40s lows occurred prior to 1978. They were 48 in 1968 (same temperature and year as the record set at Midway) and 44 in 1965.

In 1987, Rockford had 10 inches of snow today. O'Hare only had a trace from the storm.

There were three instances of back-to-back years in which temperatures were just about as opposite as they can be. 1. In 1984 the high was 47 with a low of 32, overall 11.5 degrees ABOVE normal. Then in 1985 the high was 22 with a low of 9, overall 12.5 degrees BELOW normal. 2. In 1989 the high was 17 with a low of 5, overall 17 degrees BELOW normal. Then in 1990 the high was 55 with a low of 35, overall 17 degrees ABOVE normal. 3. In 2000 the high was 15 with a low of -8, overall 24.5 degrees BELOW normal. Then in 2001 the high was 47 with a low of 38, overall 14.5 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:41 and sunrise is at 7:13. Sunset is at 16:21 and twilight ends at 16:53. There's a total of 9 hours, 8 minutes of daylight today and 10 hours, 12 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 6:42 and sunrise is at 7:13. The moon is waning gibbous, having reached the full Cold or Long Nights moon two days ago at 8:36. Illumination was 97% at midnight, will be 95% at noon and 93% at midnight tonight. Moonset is at 8:44 this morning. Moonrise is at 18:34 tonight. Moonset is at 9:22 tomorrow morning. Moonlight time is 14 hours, 10 minutes which is 18 minutes shorter 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. Bill of Rights Day is in three days.