March 17: ORD

Today is March 17th. It's the 77th day of the year. 289 days remain. It's week 11 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 of record 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 47 and the normal low is 30. I've calculated the 33-year averages at 45 and 30.

On the warm side, three years ago, in 2009, the high was a record-tying 74 with a low of 41, a 33-degree spread. Last year, in 2011, the high was 67 with a low of 48. 2009 and 2011 were the second warmest March 17ths at O'Hare (until this year). In 2003 the high was 73 with a low of 40, a 33 degree spread. In 1999 the high was 59 with a low of 41. The co-record high of 74 and record warmest low of 49 were set on the same day way back in 1894, at a time when the official readings were taken adjacent to Lake Michigan. The other warm high was 63 two years ago in 2010. 25 of the past 33 highs (76%) were in the: 30s (14) and 40s (11). O'Hare had consecutive highs in the 30s & 40s as follows: ten from 1976 through 1985 and six from 1987 through 1992. Our most recent 40s high was 41 in 2002. On the warm side, seven highs (21%) were in the: 50s (3), 60s (2) and 70s (2). O'Hare's warmest March 17th (until this year) was in 1966 when the high was 76 with a low of 43. The other pre-1979 warm highs were 69 in 1969 and 66 in 1968. On the cold side, one high (3%) was in the 20s.

In looking back through the years to the first March at O'Hare in 1959, the following instances were notable: In 1978 the high was a cold 34 with a low of 19, a cold day. In 1976 the low was a cold 18 degrees. In 1969 the high was a warm 69 with a low of 36, a 33 degree spread and warm day. In 1968 the high was a warm 66 with a low of 26, a 40 degree spread. In 1967 the high was 25 with a low of 11, a cold day. In 1966 the high was 76 with a low of 43, a 33 degree spread and warm day. And although this high of 76 beats the record of 74, O'Hare was not the official station of record in 1966. In 1964 the high was 31 with a low of 14, a cold day. In 1961 the high was a cold 34 degrees. In 1960 the high was a cold 30 with a low of 23, a seven degree spread and cold day. In 1959 the high was 27 with a low of 15, a cold day.

More recently, we had small spreads of five degrees in 1984 (32/27), six degrees in: 1989 (35/29), 1998 (39/33), 2005 (35/29) and seven degrees in 2002 (41/34). There was a large spread of 31 degrees two years ago, in 2010 (63/32).

On the cold side, in 1993 the high was 29 with a low of 12. In 1981 the high was 38 with a low of 18. The other cold highs were 32 in 1984 and 35 in three years: 1989, 1996 and 2005. The record low of -1 was set way back in 1900. The record coldest high of 11 occurred back in 1941. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 26 of the last 33 lows (79%) were in the: 20s (13) and 30s (13). O'Hare recorded 11 consecutive lows in the 20s & 30s from 1982 through 1992. Three lows (9%) were in the cold 10s (a.k.a. teens). O'Hare's coldest March 17th was in 1967 when the high was 25 (the coldest high of the date) with a low of 11 (the coldest low of the date). 1959 was also very cold as the high was 27 with a low of 15. The other pre-1979 cold lows were 14 in 1964, 18 in 1976 and 19 in 1978. Four lows (12%) were in the warm 40s.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:33 and sunrise is at 7:01. Sunset is at 19:03 and twilight ends at 19:31. There's a total of 12 hours, 2 minutes of daylight today and 12 hours, 58 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 6:31 and sunrise is at 6:59. The moon is waning crescent. Illumination was 27% at midnight, will be 23% at noon and 18% at midnight tonight. Moonrise is at 4:08 this morning. Moonset is at 14:22 this afternoon. Moonrise is at 4:42 tomorrow morning. Moonlight time is 10 hours, 14 minutes which is 25 minutes longer than yesterday.

Spring began on March 12th and runs for 84 days through June 3rd. Cool Spring began on March 12th and runs for 32 days through April 12th. High temperatures in this period are usually in the 30s, 40s and 50s. Highs in the 60s and 70s usually occur infrequently. St. Patrick's Day is today. April Fools' Day and Palm Sunday are in 15 days.