March 18: ORD

Today is March 18th. It's the 78th day of the year. 288 days remain. It's week 12 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 46 and 29.

On the warm side, in 1979 the high was 70 with a low of 43. Two years ago, in 2010, the high was 61 with a low of 41. The other warm highs were 66 in 1995 and 59 in 1986. The other warm low was 42 in 2009. The record high of 74 was most recently set in 1969 at Midway. The record high of 74 was originally set in 1903 and again in 1918, both at a time when the official readings were taken adjacent to Lake Michigan. The record warmest low of 59 occurred way back in 1894, also at a time when the official readings were taken adjacent to Lake Michigan. 18 of the past 33 highs (55%) were in the 40s. O'Hare recorded ten consecutive 40s highs from 1999 through 2008. On the warm side, eight highs (24%) were in the: 50s (5), 60s (2) and 70s (1). On the cold side, seven highs (21%) were in the: 20s (1) and 30s (6). Our most recent 30s high was 37 in 1997. 1969 rivals 1979 as O'Hare's warmest day (until this year!). In 1969 the high was 74 (O'Hare's warmest high of the date) with a low of 38. The other pre-1979 warm highs are 69 in 1976, 65 in 1968, 61 in 1966 and 59 in 1975.

In looking back through the years to the first March at O'Hare in 1959, the following instances were notable: In 1976 the high was a warm 69 with a low of 34, a 35 degree spread and warm day. In 1975 the high was 59 with a low of 43, a warm day. In 1971 the high was 39 with a low of 34, a five degree spread. In 1969 the high was a warm 74 with a low of 38, a 36 degree spread, year of the record high and warm day. 1969 is also the year of the record high of 74 at Midway. In 1968 the high was a warm 65 with a low of 40, a warm day. In 1967 the high was 33 with a low of 11, a cold day. In 1966 the high was 61 with a low of 43, a warm day. In 1965 the high was 24 with a low of 10, a cold day. In 1964 the high was 37 with a cold low of 9, another cold day. In 1961 the high was a cold 34 degrees. In 1960 the high was 31 with a low of 17, a cold day. In 1959 the low was a cold 17 degrees.

More recently, we had small spreads of four degrees in 1984 (31/27), five degrees in 1983 (40/35), six degrees in 1987 (42/36), six degrees in 2008 (42/36), seven degrees in 1992 (36/29) and seven degrees in 2003 (44/37). There was a large spread of 32 degrees in 1995 (66/34).

On the cold side, in 1993 the high was 31 with a low of 14. Four years prior, in 1989, the high was 29 with a low of 17. In 1981 the high was 35 with a low of 15. The other cold low was 18 in 1985. The other cold high was 31 in 1984. The record low of 3 was set back in 1923. The record coldest high of 20 occurred way back in 1875. 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 (14) and 30s (12). O'Hare recorded 15 consecutive lows in the 20s & 30s from 1994 through 2008. Four lows (12%) were in the cold 10s (a.k.a. teens). Our most recent 10s (a.k.a. teens) low was 14 in 1993. O'Hare's coldest March 18 was in 1965. The high was the coldest of the date (24 degrees) with a low of 10. O'Hare's coldest low of the date, 9 degrees, occurred in the previous year of 1964. The other pre-1979 cold lows were 11 in 1967 and 17 in 1960. Three lows (9%) were in the warm 40s. Prior to 1979, O'Hare's warm lows of the date were 43 degrees in both 1966 and 1975.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:31 and sunrise is at 6:59. Sunset is at 19:04 and twilight ends at 19:32. There's a total of 12 hours, 5 minutes of daylight today and 13 hours, 1 minute between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 6:30 and sunrise is at 6:57. The moon is waning crescent. Illumination was 18% at midnight, will be 15% at noon and 11% at midnight tonight. Moonrise is at 4:42 this morning. Moonset is at 15:27 this afternoon. Moonrise is at 5:12 tomorrow morning. Moonlight time is 10 hours, 45 minutes which is 31 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. April Fools' Day and Palm Sunday are in 14 days.