December 16: ORD

Today is December 16th. It's the 350th day of the year. 15 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 34 and the normal low is 20. I've calculated the 33-year averages at 34 and 21.

On the warm side, in 1984 the high was the record high of 60 with a low of 37. In 2006 the high was 55 with a low of 32. Five years earlier, in 2001, the high was 45 with a low of 39, a six degree spread. In 1997 the high was 45 with a low of 32. The other warm lows were 35 in 1986, 34 in 1994, 33 in 1990, 33 in 1993 and 32 in 1998. The record warmest low of 43 was set back in 1928, at a time when the official readings were taken adjacent to Lake Michigan. 29 of the past 33 highs (88%) were in the: 20s (8), 30s (13) and 40s (8). Our last four highs were in the 20s (2007-2010). Our most recent 30s high was 33 in 2002. Two highs were in the warm: 50s (1) and 60s (1). The pre-1978 warm highs were 54 in 1977 and 51 in 1959. Two highs were in the cold: 0s (a.k.a. single digits) (1) and 10s (a.k.a. teens) (1). The pre-1978 cold highs were 15 in 1963 and 9 in 1972 (tied with 9 in 1989 as O'Hare's coldest highs for the date).

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 a warm 54 with a low of 30, a warm day. In 1974 the high was 36 with a low of 30, a six degree spread. In 1972 the high was 9 with a low of -2, a cold day. In 1971 the high was 39 with a warm low of 33, a six degree spread. In 1970 the high was 39 with a warm low of 36, a mere three degree spread. In 1966 the high was 34 with a warm low of 32, a mere two degree spread. In 1965 the high was 30 with a low of 24, a six degree spread. In 1963 the high was 15 with a low of -6, a cold day. In 1959 the high was 51 with a low of 35, a warm day. In 1958 the high was 36 with a cold low of 0, a 36 degree spread.

More recently, there was a large spread of 32 degrees in 1979 (37/5). There were small spreads of three degrees in 1980 (33/30), three degrees in 1990 (36/33), three degrees in 2002 (33/30), five degrees in 1986 (40/35), five degrees in 1994 (39/34), six degrees in 1996 (32/26), six degrees in 2005 (24/18), seven degrees in 1993 (40/33) and seven degrees last year, in 2010 (27/20).

On the cold side, in 1989 the high was 9 (tied with 9 in 1972 as O'Hare's coldest highs for the date) with a low of -5. A year earlier, in 1988, the high was 17 with a low of 4. Three years prior, in 1985, the high was 23 with a low of 3. Two years before that, in 1983, the high was 23 with a low of 3. Two years ago, in 2009, the high was 23 with a low of 5. Three years ago, in 2008, the high was 22 with a low of 6. Both 2008 & 2009 were 13 degrees below normal, having nearly the same highs & lows! In 1981 the high was 22 with a low of 9. The other cold lows were 5 in 1979 and 6 in 1991. The record low of -12 and record coldest high of 2 were set on the same cold day in 1951 at Midway. 20 of the last 33 lows (61%) were in the: 20s (8) and 30s (12). O'Hare has not had a low in the warm 40s for the date. 13 lows (39%) were in the cold: negative 0s (1), 0s (a.k.a. single digits) (8) and 10s (a.k.a. teens) (4). Pre-1978, the cold lows were -2 in 1972 and -6 in 1963 (O'Hare's coldest low of the date).

There was an instance of back-to-back-to-back years in which temperatures were just about as opposite as they can be: in 1983 the high was 23 with a low of 3, overall 14 degrees BELOW normal. Then in 1984 the high was 60 with a low of 37, overall 21.5 degrees ABOVE normal. Then in 1985 the high was 23 with a low of 3, overall 14 degrees BELOW normal. Note the same cold temperatures are sandwiching 1984, the year of the record high!

In 1973, O'Hare had 4.5 inches of snow today. This was the fourth 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.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:44 and sunrise is at 7:16. Sunset is at 16:22 and twilight ends at 16:54. There's a total of 9 hours, 6 minutes of daylight today and 10 hours, 10 minutes between twilights. We lost a minute of daylight from yesterday. Tomorrow twilight begins at 6:44 and sunrise is at 7:16. The moon is waning gibbous and reaches last quarter tomorrow at 18:48. Illumination was 69% at midnight, will be 64% at noon and 59% at midnight tonight. Moonset is at 10:55 this morning. Moonrise is at 23:01 tonight. Moonset is at 11:24 tomorrow morning. Moonlight time is 11 hours, 54 minutes which is 40 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. Christmas Eve is in eight days. Christmas is in nine days.