December 20: ORD

Today is December 20th. It's the 355th day of the year. 11 days remain. It's week 51 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. Observations have been official at O'Hare since Thursday, January 17, 1980.

According to the National Climatic Data Center (NCDC), the normal high is 33 and the normal low is 19. The 30-year averages are 32 and 17.

On the warmer side, in 1988 the high was 56 with a low of 32. Two years later, in 1990, the high was 49 with a low of 30. Four years later, in 1994, the high was 42 with a low of 34. In 1979 the high was 44 with a low of 29. Another warm low was 30 in 1991. The record high of 67 and record warmest low of 55 occurred on the same day way back in 1877. 19 of the last 30 highs were 30s (12) and 40s (7). Even warmer, one high (56 above) was in the 50s. On the colder side, five highs were 20s, four highs were 10s and one high was a 0s high.

In looking back through the years to the first December at O'Hare in 1958, the following instances were notable. In 1972 the high was 37 with a low of 34, a three degree spread. In 1968 the high was 33 with a low of 26, a seven degree spread. In 1966 the high was 36 with a low of 32, a four degree spread. In 1965 the high was 35 with a low of 29, a six degree spread. In 1963 the high was 6 with a low of -16, a cold day. This high of 6 was near the record coldest high of 4, set in 1901. Although the low was -16 in 1963, O'Hare was not the station of record for Chicago at the time, so therefore the record is -9, established in 1963 at Midway. In 1959 the high was 31 with a low of 28, a three degree spread.

More recently, we had a small spread of five degrees in 1991 (35/30) and six degrees in 2002 (35/29). In 1999 we had our only large spread of 32 degrees as the high was 37 with a low of 5.

On the cold side, in 1989 the high was the near-record coldest high of 5 with a low of -6. The record coldest high of 4 was set in 1901. In 1980 the high was 10 with a low of -1. Two decades later, in 2000, the high was 17 with a low of -5. In 1983 the high was 20 with a low of -1. In 1996 the high was 17 with a low of 3. In 1981 the high was 22 with a low of -1. Four years later, in 1985, the high was 19 with a low of 3. Two decades later, in 2005, the high was 21 with a low of 5. Another cold low was 5 in 1999. The record low of -9 was set in 1963, although, as mentioned above, it was colder at O'Hare that day. 13 of the last 30 lows were 20s. On the warmer side, four lows were 30s. On the colder side, four lows were 10s, four lows were 0s and five lows were negative 0s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:47 and sunrise is at 7:18. Sunset is at 16:24 and twilight ends at 16:56. There's a total of 9 hours, 6 minutes of daylight today and 10 hours, 9 minutes between twilights. Tomorrow twilight begins at 6:47 and sunrise is at 7:19. The moon reached last quarter yesterday at 4:29. The moon is waning crescent. Illumination was 42% at midnight, will be 37% at noon and 32% at midnight tonight. Moonrise was at 0:50 and moonset is at 12:04. Moonrise is at 1:55 tomorrow. Moonlight time is 11 hours, 14 minutes today.

Today is a major snow day in O'Hare's history. In 1973, 0.1 inches fell. This was the eighth of eight days of measurable snowfall, part of 17.6 inches that fell. This comprised 94% of the month's total of 18.8 inches. At Midway in 1960, 11 inches fell while at O'Hare, only 3.1 inches fell, following 1.1 inches on the 19th.

Christmas Eve is in four days and Christmas Day is in five days. New Year's Eve is in 11 days and New Year's Day is in 12 days. -Bernie-