March 15: ORD

Today is March 15th. It's the 75th day of the year. 291 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 46 and the normal low is 29. I've calculated the 33-year averages at 46 and 28.

On the warm side, in 1995 (until 2012 this was O'Hare's warmest March 15th) the high was the record high (now former record high) of 74 with a low of 43, a 31 degree spread. Five years prior, in 1990, the high was 68 with a low of 45 (O'Hare's warmest low of the date). In 2000 the high was 65 with a low of 34, a 31 degree spread. The other warm highs were 62 in 1981, 59 in 2002 and 58 three years ago in 2009. The record warmest low of 49 occurred back in 1945 at Midway. 27 of the past 33 highs (82%) were in the: 30s (8), 40s (13) and 50s (6). On the warm side, four highs were in the: 60s (3) and 70s (1). O'Hare's second warmest day of the date was in 1977 when the high was 71 with a low of 44. The other pre-1979 warm highs were 60 in 1968 and 58 in 1971. On the cold side, two highs were in the 20s. O'Hare's only 20s high, pre-1979, was 28 in 1962.

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 36 with a low of 31, a five degree spread. In 1977 the high was 71 with a low of 44, a warm day. In 1973 the low was a warm 41 degrees. In 1971 the high was a warm 58 degrees. In 1970 the high was 33 with a low of 16, a cold day. In 1968 the high was a warm 60 with a low of 39, a warm day. In 1967 the high was a cold 34 degrees. In 1962 the high was a cold 28 with a low of 21, a seven degree spread and cold day. In 1960 the high was a cold 33 degrees.

More recently, we had small spreads of six degrees in 1987 (38/32), seven degrees in 1982 (43/36) and seven degrees in 1986 (41/34). The other large spreads were 34 degrees in 1993 (47/13), 32 degrees in 1981 (62/30) and 30 degrees three years ago in 2009 (58/28).

On the cold side, in 1997 the high was 26 with a low of 13. In 1979 the high was 25 with a low of 15. 1997 and 1979 were O'Hare's coldest March 15 days. In 1988 the high was 30 with a low of 17. The other cold low was 13 in 1993. The lows of 13 were O'Hare's coldest of the date. The other cold high was 32 in 1998. The record low of 6 was last set way back in 1890, having originally occurred way back in 1877. The record coldest high of 17 occurred way back in 1893. Both records were set at a time when the official readings were taken adjacent to Lake Michigan. 27 of the last 33 lows (82%) were in the: 20s (16) and 30s (11). O'Hare had consecutive lows in the 20s & 30s as follows: eight from 1980 through 1987 and 14 from 1998 through last year, 2011. 22 of the 27 lows (81%) in the 20s & 30s occurred in these two streaks. Four lows were in the cold 10s (a.k.a. teens). Our most recent 10s low was 13 in 1997. O'Hare's only pre-1979 10s low was 16 in 1970. On the warm side, two lows were in the 40s. Prior to 1979, O'Hare had a warm low of 41 in 1973.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 6:36 and sunrise is at 7:04. Sunset is at 19:00 and twilight ends at 19:28. There's a total of 11 hours, 56 minutes of daylight today and 12 hours, 52 minutes between twilights. We gained three minutes of daylight from yesterday. Tomorrow twilight begins at 6:35 and sunrise is at 7:03. The moon is waning crescent, having reached last quarter last night at 20:25. Illumination was 48% at midnight, will be 43% at noon and 37% at midnight tonight. Moonrise is at 2:39 this morning. Moonset is at 12:12 this afternoon. Moonrise is at 3:27 tomorrow morning. Moonlight time is 9 hours, 33 minutes which is five 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 in two days.