May 16: ORD

Today is May 16th. It's the 137th day of the year. 229 days remain. It's week 20 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 70 and the normal low is 48. I've calculated the 33-year averages at 70 and 47.

On the warm side, in 2001 (O'Hare's second warmest May 16th) the high was 89 (our most recent 80s high) with a low of 64. A decade earlier, in 1991, the high was 86 with a low of 63. The next year, 1992, the high was 88 with a low of 58, a 30 degree spread. In 1998 the high was 82 with a low of 62. In 1986 the high was 79 with a low of 62. The other warm highs were all 83 degrees: in 1982, 1987 and 1999. The other warm lows were 60 in 1990 and 59 in 1995. The record high of 94 and record warmest low of 69 were set on the same day in 1962 at Midway. 16 of the past 33 highs (49%) were in the 60s. 15 highs (45%) were in the warm: 70s (8) and 80s (7). Two highs (6%) were in the cold 50s. O'Hare's warmest May 16th was in 1962 as the high was 92 (O'Hare's warmest high of the date) with a low of 69 (O'Hare's warmest low of the date).  

In looking back through the years to the first May at O'Hare in 1959, the following instances were notable: In 1977 the high was 86 with a low of 61, a hot day. In 1969 the high was 85 with a low of 60, a very warm day. In 1962 the high was 92 with a low of 69, a hot day. 1962 was also the year of the record high of 94 and record warmest low of 69 at Midway.

More recently, we had a small spread of 6 degrees in 1996 (57/51). The additional large spreads were 40 degrees in 1987 (83/43), 35 degrees in 1997 (68/33), 33 degrees in 2004 (70/37), 33 degrees in 2008 (73/40) and 32 degrees in 1981 (75/43).

On the cool side, last year, in 2011 (O'Hare's coldest May 16th), the high was 52 (O'Hare's coldest high of the date) with a low of 37. In 1983 the high was 63 with a low of 35. The other cold lows were the record low of 33 in 1997 and a low of 36 in 1984. The former record low of 34 was set way back in 1888. The record coldest high of 44 occurred way back in 1891, at a time when the official readings were taken adjacent to Lake Michigan. 17 of the last 33 lows (52%) were in the 40s. There were six consecutive 40s lows from 2005 through 2010. Five lows (15%) were in the cold 30s. 11 lows (33%) were in the warm: 50s (6) and 60s (5). Our most recent 50s low was 54 in 2000. Our most recent 60s low was 64 in 2001.

The following astronomical data is provided by the United States Naval Observatory. In Crystal Lake, twilight begins at 4:59 and sunrise is at 5:31. Sunset is at 20:09 and twilight ends at 20:42. There's a total of 14 hours, 38 minutes of daylight today and 15 hours, 43 minutes between twilights. We gained two minutes of daylight from yesterday. Tomorrow twilight begins at 4:57 and sunrise is at 5:30. The moon is waning crescent. Illumination was 19% at midnight, will be 15% at noon and 12% at midnight tonight. Moonrise was at 3:05 this morning. Moonset is at 16:21 this afternoon. Moonrise is at 3:32 tomorrow morning. Moonlight time is 13 hours, 16 minutes which is 33 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. Armed Forces Day is in three days. National Maritime Day is in six days.