December 1: ORD

Today is December 1st. It's the 335th day of the year. 30 days remain. It's week 48 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 40 and the normal low is 26. I've calculated the 33-year averages at 40 and 26.

On the warm side, in 1982 the high was 63 (the only 60s high of the past 33 years) with a low of 49 (the only 40s low of the past 33 years). In 1998 the high was 57 with a low of 33. The other warm highs were 55 two years ago, in 2009 and 52 in 1994. The record high of 68 was set in 1970 at Midway. The record warmest low of 52 occurred back in 1914, at a time when the official readings were taken adjacent to Lake Michigan. 23 of the past 33 highs (70%) were in the: 30s (12) and 40s (11). There were six consecutive highs in the 30s & 40s from 1999 through 2004. Our most recent 40s high was 41 in 2003. Five highs were in the warm: 50s (4) and 60s (1). O'Hare's other 60s highs (all pre-1978) were 67 in 1970 and 64 in 1962. Five highs were in the cold 20s.

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 a cold 24 with a low of 16, a cold day. There was a big 46 degree drop in 1975. In 1975, the high on November 30 was 62 and today's low was 16. In 1974 the high was 38 with a low of 32, a six degree spread. In 1972 the low was a cold 13 degrees. In 1970 the high was 67 with a low of 46, a warm day. 1970 was also the year of the record high of 68 at Midway. In 1968 the high was 37 with a low of 32, a five degree spread. In 1967 the high was 34 with a low of 27, a seven degree spread. In 1966 the high was 25 with a low of 7, a cold day. In 1964 the high was 24 with a low of 11, a cold day. In 1963 the high was 29 with a cold low of 11, a cold day. In 1962 the high was a warm 64 with a low of 25, a 39 degree spread and warm day. Also in 1962, the high temperature was 64 degrees for three days in a row on 11/30, 12/1 and 12/2. What a treat that was! In 1960 the low was a cold 12 degrees.

More recently, there was a large spread of 39 degrees in 1985 (50/11). There were small spreads of four degrees in 1992 (34/30), five degrees in 1987 (34/29), five degrees in 2000 (36/31), seven degrees in 1986 (42/35), seven degrees in 1997 (41/34) and seven degrees in 2004 (32/25).

In 2006, Rockford received 10.7 inches of snow while 5.8 inches fell at O'Hare.

On the cold side, in 1983 the high was 25 with a low of 18, a seven degree spread. Last year, in 2010, the high was 26 with a low of 22, a four degree spread. In 1988 the high was 28 with a low of 20. The other cold lows were 11 in 1985 and 13 in 2002. The record low of -6 and record coldest high of 2 were set on the same cold day way back in 1893, at a time when the official readings were taken adjacent to Lake Michigan. 27 of the last 33 lows (82%) were in the: 20s (16) and 30s (11). There were 16 consecutive lows in the 20s & 30s from 1986 through 2001. Five lows were in the cold 10s (a.k.a. teens), the most recent were 18 in 2006 and 19 in 2007. The coldest temperature O'Hare ever had on the date (and only single digit low) was 7 degrees in 1966. One low was in the warm 40s. The only other 40s low was 46 in 1970.

There was an instance of back-to-back years in which temperatures were just about as opposite as they can be. In 1982 the high was 63 with a low of 49, overall 23 degrees ABOVE normal. Then in 1983 the high was 25 with a low of 18, overall 11.5 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:31 and sunrise is at 7:02. Sunset is at 16:22 and twilight ends at 16:53. There's a total of 9 hours, 20 minutes of daylight today and 10 hours, 22 minutes between twilights. We lost two minutes of daylight from yesterday. Tomorrow twilight begins at 6:32 and sunrise is at 7:03. The moon is waxing crescent. Illumination was 39% at midnight, will be 44% at noon and 49% at midnight tonight. Moonrise is at 11:42 this morning. Moonset is at 23:25 tonight. Moonrise is at 12:07 tomorrow afternoon. Moonlight time is 11 hours, 43 minutes which is 35 minutes longer than yesterday.

Winter begins today and runs for 102 days through March 11. 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 six days. Bill of Rights Day is in 14 days.