December 14: ORD

Today is December 14th. It's the 348th day of the year. 17 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 37 and 23.

On the warm side, in 2006 the high was 50 with a low of 35. In 1993 the high was 44 with a low of 38, a six degree spread. In 2008 the high was 50 with a low of 31. Note how the two 50s highs occurred recently. The other warm highs were 47 in 1988 and 47 a decade later in 1998. The other warm low was 36 in 1999. The record high of 66 and record warmest low of 47 were set on the same warm day in 1975 at Midway. 25 of the past 33 highs (76%) were in the: 30s (16) and 40s (9). Our most recent 40s high (40 in 1999) was the last of five straight years of 40s highs from 1995 through 1999. There were eight consecutive 30s & 40s highs from 1977 through 1984. The first seven of those eight were in the 30s (from 1977 through 1983). There were another ten consecutive 30s & 40s highs from 1990 through 1999. Two highs were in the warm 50s. O'Hare's warmest high for the date was 64 in 1975. Six highs were in the cold: 10s (a.k.a. teens) (2) and 20s (4). Pre-1978, the coldest highs were 11 in 1963 and 12 in 1958. Both of these were colder than the coldest highs from 1978 onward.

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 36 with a warm low of 33, a small three degree spread. In 1975 the high was 64 with a low of 44, a warm day, year of the record high of 66 and record warmest low of 47 at Midway. In 1974 the high was 41 with a warm low of 35, a six degree spread. In 1972 the high was 26 with a cold low of 2, a cold day. In 1965 the high was 35 with a low of 31, a four degree spread. In 1963 the high was 11 with a low of -6, a cold day. In 1962 the high was 26 with a cold low of 2, a cold day. In 1959 the high was 40 with a warm low of 33, a seven degree spread. In 1958 the high was 12 with a low of -3, a cold day.

More recently, there were no large spreads of 30 degrees or more. There were small spreads of four degrees in 1999 (40/36), six degrees in 1992 (32/26), six degrees in 2003 (31/25), seven degrees in 2001 (38/31), seven degrees in 2002 (38/31) and seven degrees in 2005 (35/28).

On the cold side, in 1985 the high was 16 with a low of -8 (O'Hare's coldest for the date). Four years later, in 1989, the high was 18 (our most recent 10s high) with a low of -3. As you can see, the negative lows occurred back in the 1980's, just four years apart. Last year, in 2010, the high was 21 with a low of 6. A decade earlier, in 2000, the high was 26 with a low of 7. The record low of -9 was set way back in 1901. The record coldest high of 5 occurred way back in 1903. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 16 of the last 33 lows (49%) were in the 20s. Nine lows (27%) were in the cold: negative 0s (2), 0s (a.k.a. single digits) (2) and 10s (a.k.a. teens) (5). Prior to 1978, the coldest lows were -6 in 1963 and -3 in 1958. Eight lows (24%) were in the warm 30s. O'Hare's warmest low for the date was 44 in 1975.

In 1973, O'Hare had 0.3 inches of snow today. This was the second day of a string of days through the 20th which produced 17.6 inches, or 94% of the month's total of 18.8 inches. In 1987, O'Hare had 1.1 inches, part of a two-day storm of 9.1 inches. In 1951 Midway had ten inches.

There were two instances of back-to-back years in which temperatures were just about as opposite as they can be: 1. In 1984 the high was 45 with a low of 32, overall 10.5 degrees ABOVE normal. Then in 1985 the high was 16 with a low of -8, overall 24 degrees BELOW normal. 2. In 1999 the high was 40 with a low of 36, overall 10 degrees ABOVE normal. Then in 2000 the high was 26 with a low of 7, overall 11.5 degrees BELOW normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:42 and sunrise is at 7:14. Sunset is at 16:22 and twilight ends at 16:53. There's a total of 9 hours, 8 minutes of daylight today and 10 hours, 11 minutes between twilights. We lost no minutes of daylight from yesterday. Tomorrow twilight begins at 6:43 and sunrise is at 7:15. The moon is waning gibbous. Illumination was 87% at midnight, will be 83% at noon and 79% at midnight tonight. Moonset is at 9:56 this morning. Moonrise is at 20:45 tonight. Moonset is at 10:27 tomorrow morning. Moonlight time is 13 hours, 11 minutes which is 33 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 tomorrow.