December 9: ORD

Today is December 9th. It's the 343rd day of the year. 22 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 37 and the normal low is 22. I've calculated the 33-year averages at 36 and 21.

On the warm side, in 1987 the high was 59 (O'Hare's warmest high of the date) with a low of 40. In 2003 the high was 49 (our most recent 40s high) with a low of 41 (our most recent 40s low). In the following year of 2004, the high was 50 (our most recent 50s high) with a low of 37 (our most recent 30s low). In 1999 the high was 53 with a low of 33. In 1990 the high was 55 with a low of 30. In 1993 the high was 51 with a low of 33. The record high of 62 was set way back in 1879, at a time when the official readings were taken adjacent to Lake Michigan. The record warmest low of 56 occurred back in 1946 at Midway. 14 of the past 33 highs (43%) were in the 30s. 12 highs (36%) were in the warm: 40s (7) and 50s (5). The warmest pre-1978 high at O'Hare was 50 in 1965. Seven highs (21%) were in the cold: 0s (1), 10s (1) and 20s (5). Highs over the past six years were in the 20s & 30s (2005-2010). The pre-1978 cold highs were 3 in 1958 and 16 in 1977.

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 16 with a low of -5, a cold day. In 1974 the high was a cold 25 degrees. In 1972 the high was 21 with a low of 9, a cold day. In 1971 the high was 48 with a warm low of 42, a six degree spread and warm day. In 1967 the high was 41 with a warm low of 36, a five degree spread. In 1966 the high was 38 with a warm low of 34, a four degree spread. In 1965 the high was a warm 50 degrees. Also in 1965, it was the first of four consecutive highs in the 50s. In 1964 the high was 28 with a cold low of 7, a cold day. In 1962 the high was a cold 23 degrees. In 1961 the high was 32 with a low of 27, a five degree spread. In 1958 the high was 3 with a low of -14, a cold day. That low of -14 unofficially ties the record low set way back in 1876. The high of 3 was near the record coldest high of 2, also set way back in 1876.

More recently, there were no large spreads of 30 degrees or more. There were small spreads of five degrees in 1994 (33/28), five degrees in 1996 (31/26), five degrees in 1997 (35/30), six degrees in 1980 (33/27) and seven degrees in 2007 (29/22).

On the cold side, in 1995 the high was 5 with a low of -4. In 1978 the high was 13 with a low of -2. In 2000 the high was 30 with a low of 2. Last year, in 2010, the high was 29 with a low of 5. The other cold low was 8 in 2002. The record low of -14 and record coldest high of 2 were set on the same cold day way back in 1876, at a time when the official readings were taken adjacent to Lake Michigan. 20 of the last 33 lows (61%) were in the: 10s (8) and 20s (12). Eight consecutive lows from 1979-1986 were in the 10s & 20s. Five lows (15%) were in the cold: negative 0s (2) and 0s (3). O'Hare's coldest pre-1978 lows were: -14 in 1958 (tied with the official record low set way back in 1876), -5 in 1977, 7 in 1964 and 9 in 1972. Eight lows (24%) were in the warm: 30s (6) and 40s (2). O'Hare's warmest low was 42 in 1971.

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1999 the high was 53 with a low of 33, overall 14 degrees ABOVE normal. Then in 2000 the high was 30 with a low of 2, overall 13 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:38 and sunrise is at 7:10. Sunset is at 16:21 and twilight ends at 16:53. There's a total of 9 hours, 11 minutes of daylight today and 10 hours, 15 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 6:39 and sunrise is at 7:11. The moon is waxing gibbous and will reach the full Cold or Long Nights moon tomorrow at 8:36. Illumination was 98% at midnight, will be 99% at noon and 100% at midnight tonight. Moonset is at 6:17 this morning. Moonrise is at 15:45 this afternoon. Moonset is at 7:11 tomorrow morning. Moonlight time is 14 hours, 32 minutes which is 13 minutes longer than yesterday. Moonlight time is at it's peak, just when it is full. It doesn't get any better than this!

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 six days.