February 17: ORD

Today is February 17th. It's the 48th day of the year. 318 days remain. It's week 7 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. 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 36 and the normal low is 21. I've calculated the 33-year averages at 35 and 22.

On the warm side, last year, in 2011, the high was 56 with the new record warmest low of 47. The former record warmest low of 42 was set way back in 1890, at a time when the official readings were taken adjacent to Lake Michigan. In 1981 the high was 58 (O'Hare's warmest high of the date) with a low of 39. In 1994 the high was 51 with a low of 34. Four years later, in 1998, the high was 43 with a low of 39, a mere four degree spread. The other warm lows were 36 in 1992, 35 in 1984 and 33 in 1983. The record high of 60 was set way back in 1880, at a time when the official readings were taken adjacent to Lake Michigan. 27 of the past 33 highs (82%) were in the: 20s (6), 30s (13) and 40s (8). On the warm side, three highs were in the 50s. O'Hare's only pre-1979 50s high was 50 in 1961. On the cold side, three highs were in the 10s (a.k.a. teens). O'Hare had a high of 19 in 1978, its coldest prior to 1979.

In looking back through the years to the first February at O'Hare in 1959, the following instances were notable: In 1978, the high was 19 with a low of -2, a cold day. In 1976 the high was 42 with a warm low of 36, a six degree spread. In 1975 the high was 36 with a warm low of 33, a three degree spread. In 1973 the high was 21 with a low of 2, a cold day. In 1971 the high was 46 with a warm low of 36, a warm day. In 1968 the high was 22 with a low of 1, a cold day. In 1967 the low was a cold 8 degrees. In 1966 the high was 24 with a low of 7, a cold day. In 1962 the high was 32 with a low of 27, a five degree spread. In 1961 the high was 50 with a low of 37, a warm day.

More recently, there were small spreads of four degrees on two occasions: 1983 (37/33) and 1992 (40/36). There was a small spread of five degrees in 1982 (37/32). Spreads of six degrees occurred in: 1986 (36/30) and two years ago, in 2010 (32/26).

On the cold side, in 1980 the high was 14 with a low of -5 (O'Hare's coldest low of the date). In the prior year, 1979, the high was 12 (O'Hare's coldest high of the date) with a low of 3. In 1993 the high was 20 with a low of 0. In 2001 the high was 19 with a low of 6. Five years later, in 2006, the high was 24 with a low of 3. The other cold low was 9 in 1989. The record low of -11 and record coldest high of 1 were set on the same cold day back in 1903, at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 10s (a.k.a. teens) (8), 20s (9) and 30s (9). Even colder, six lows were in the: negative single digits (1) and single digits (5). O'Hare had a low of -2 in 1978. 1978 through 1980 were the coldest years for February 17. The highs, lows and departures from normal for these years: 1978: 19/-2 (-19.5), 1979: 12/3 (-20.5) and 1980: 14/-5 (-23.5). Finally, 1981 broke the cold trend as it was 20.5 degrees above normal (58/39). On the warm side, one low (last year's record warmest of 47) was in the 40s.

There were two instances of back-to-back years in which temperatures were just about as opposite as they can be. In the first instance, in 1980 the high was 14 with a low of -5, overall 23.5 degrees BELOW normal. Then in 1981 the high was 58 with a low of 39, overall 20.5 degrees ABOVE normal. In the second instance, in 1993 the high was 20 with a low of 0, overall 18 degrees BELOW normal. Then in 1994 the high was 51 with a low of 34, overall 14.5 degrees ABOVE normal.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:19 and sunrise is at 6:47. Sunset is at 17:28 and twilight ends at 17:56. There's a total of 10 hours, 41 minutes of daylight today and 11 hours, 37 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 6:17 and sunrise is at 6:46. The moon is waning crescent. Illumination was 23% at midnight, will be 19% at noon and 15% at midnight tonight. Moonrise was at 3:42 this morning. Moonset was at 13:17 this afternoon. Moonrise is at 4:28 tomorrow morning. Moonlight time is 9 hours, 35 minutes which is nine minutes longer 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. Presidents' Day is in three days. Mardi Gras is in four days. George Washington's Birthday and Ash Wednesday are in five days.