May 12: ORD

Today is May 12th. It's the 133rd day of the year. 233 days remain. It's week 19 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. From Friday, January 1, 1926 through Tuesday, June 30, 1942, the official site was at the University of Chicago. 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 69 and the normal low is 47. I've calculated the 33-year averages at 67 and 47.

On the warm side, in 2004 (O'Hare's warmest May 12th) the high was 85 with the record warmest low of 66 (our most recent 60s low). The record warmest low of 66 originally occurred in 1956 at Midway. In 1991 the high was 84 with a low of 63. In 2000 the high was 85 with a low of 60. Last year, in 2011, the high was 86 (O'Hare's warmest high of the date) with a low of 58. In 1992 the high was 77 with a low of 62. The other warm highs were 84 in 1993 and 81 in 1982. The record high of 92 was set in 1956 at Midway. 32 of the past 33 highs (97%) were in the: 50s (9), 60s (8), 70s (7) and 80s (8). On the cold side, one high was in the 40s.  

In looking back through the years to the first May at O'Hare in 1959, the following instances were notable: In 1974 the high was a cool 55 with a low of 48, a seven degree spread. In 1973 the high was a cool 56 degrees. In 1971 the high was a cool 57 degrees. In 1970 the high was a warm 81 with a low of 49, a 32 degree spread. In 1968 the high was 77 with a low of 46, a 31 degree spread. In 1967 the high was a cool 52 with a low of 38, a cool day. In 1966 the high was a cold 44 with a low of 40, a four degree spread and cold day. In 1965 the high was a warm 81 with a low of 47, a 34 degree spread. In 1963 the high was a cool 57 degrees. In 1961 the high was a warm 83 with a low of 50, a 33 degree spread. In 1960 the high was 59 with a cold low of 34, a cool day.

More recently, we had additional large spreads of 43 degrees in 1993 (84/41), 32 degrees in 1998 (79/47), 32 degrees in 2009 (71/39), and 30 degrees in 1982 (81/51). The small spreads were five degrees in 2002 (50/45) and seven degrees two years ago, in 2010 (51/44).

On the cool side, in 2006 (O'Hare's coldest May 12th) the high was 47 with a low of 36. A decade earlier, in 1996 (O'Hare's third coldest May 12th), the high was 50 with a low of 35. In 1981 the high was 62 with the record low of 31. The other cool highs were: 50 in 2002, 51 two years ago, in 2010, 54 in 1979, 55 in 1990, 55 in 2005, 56 in 2008 and 57 in 2001. The record coldest high of 43 occurred back in 1912. Another cold high of 44 occurred way back in 1882. Both of these instances occurred at a time when the official readings were taken adjacent to Lake Michigan. 17 of the last 33 lows (52%) were in the 40s. Six lows (18%) were in the cold 30s. Ten lows (30%) were in the warm: 50s (6) and 60s (4). O'Hare's second coldest May 12th was in 1966 with its coldest high of 44 and low of 40.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 5:03 and sunrise is at 5:35. Sunset is at 20:05 and twilight ends at 20:37. There's a total of 14 hours, 30 minutes of daylight today and 15 hours, 34 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 5:02 and sunrise is at 5:34. The moon reaches last quarter today at 16:47. Illumination was 57% at midnight, will be 52% at noon and 47% at midnight tonight. Moonrise was at 1:17 this morning. Moonset is at 12:16 this afternoon. Moonrise is at 1:47 tomorrow morning.  Moonlight time is 10 hours, 59 minutes which is 31 minutes longer than yesterday. 

Spring began on March 12th and runs for 84 days through June 3rd. Warm Spring began on April 13th and runs for 52 days through June 3rd. High temperatures in this period are usually in the 50s, 60s and 70s. Highs in the 80s and 90s occur infrequently. Mother's Day is in tomorrow. Armed Forces Day is in seven days. National Maritime Day is in ten days.